Q- What is a microprocessor?

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Ans-   

1. A microprocessor is a component that performs the instructions and tasks involved in computer processing. In a computer system, the microprocessor is the central unit that executes and manages the logical instructions passed to it. 

2. A microprocessor may also be called a processor or central processing unit, but it is actually more advanced in terms of architectural design and is built over a silicon microchip.

3. A microprocessor is the most important unit within a computer system and is responsible for processing the unique set of instructions and processes. A microprocessor is designed to execute logical and computational tasks with typical operations such as addition/subtraction, interprocess and device communication, input/output management, etc. A microprocessor is composed of integrated circuits that hold thousands of transistors; exactly how many depends on its relative computing power.

4. Microprocessors are generally classified according to the number of instructions they can process within a given time, their clock speed measured in megahertz and the number of bits used per instruction. 

     

The basic functionality of the Microprocessor is to do processing. Microprocessor performs two type of operations called Arithmetic and Logic. So the basic functionality unit which consists of Arithmetic ( Addition, Subtraction, Multiplication & Division) and Logic (AND, OR, NOT) is called Arithmetic Logic Unit.

Some of the common components of a microprocessor are:

• Control Unit.
• I/O Units.
• Arithmetic Logic Unit (ALU)
• Registers.
• Cache.

Q- What does the microprocessor contain?

Ans- A microprocessor, sometimes called a logic chip, is a computer processor on amicrochip. The microprocessor contains all, or most of, the central processing unit (CPU) functions and is the "engine" that goes into motion when you turn your computer on.

Q- Which of the following are the two main components of the microprocessor?

Ans- The two typical components of a CPU include the following:

• The arithmetic logic unit (ALU), which performs arithmetic and logical operations.
• The control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.

Q- What is microprocessor and its types?

Ans- Types of Microprocessor. Microprocessors are classified into five types, namely: CISC-Complex Instruction Set Microprocessors, RISC-Reduced Instruction SetMicroprocessor, ASIC- Application Specific Integrated Circuit, Superscalar Processors, DSP's-Digital Signal Microprocessors. Types Of Microprocessors.

Q-What are the characteristics of microprocessor?

Ans- Here are the important characteristics of processors:

Processor make and model

The primary defining characteristic of a processor is its make AMD or Intel and its model. Although competing models from the two companies have similar features and performance, you cannot install an AMD processor in an Intel-compatible motherboard or vice versa.

Socket type

Another defining characteristic of a processor is the socket that it is designed to fit. If you are replacing the processor in a Socket 478 motherboard, for example, you must choose a replacement processor that is designed to fit that socket. Table 5-1 describes upgradability issues by processor socket.

Clock speed

The clock speed of a processor, which is specified in megahertz (MHz) or gigahertz (GHz), determines its performance, but clock speeds are meaningless across processor lines. For example, a 3.2 GHz Prescott-core Pentium 4 is about 6.7% faster than a 3.0 GHz Prescott-core Pentium 4, as the relative clock speeds would suggest. However, a 3.0 GHz Celeron processor is slower than a 2.8 GHz Pentium 4, primarily because the Celeron has a smaller L2 cache and uses a slower host-bus speed. Similarly, when the Pentium 4 was introduced at 1.3 GHz, its performance was actually lower than that of the 1 GHz Pentium III processor that it was intended to replace. That was true because the Pentium 4 architecture is less efficient clock-for-clock than the earlier Pentium III architecture.

Clock speed is useless for comparing AMD and Intel processors. AMD processors run at much lower clock speeds than Intel processors, but do about 50% more work per clock tick. Broadly speaking, an AMD Athlon 64 running at 2.0 GHz has about the same overall performance as an Intel Pentium 4 running at 3.0 GHz.

'''MODEL NUMBERS VERSUS CLOCK SPEEDS'''

Because AMD is always at a clock speed disadvantage versus Intel, AMD uses model numbers rather than clock speeds to designate their processors. For example, an AMD Athlon 64 processor that runs at 2.0 GHz may have the model number 3000+, which indicates that the processor has roughly the same performance as a 3.0 GHz Intel model. (AMD fiercely denies that their model numbers are intended to be compared to Intel clock speeds, but knowledgeable observers ignore those denials.)

Intel formerly used letter designations to differentiate between processors running at the same speed, but with a different host-bus speed, core, or other characteristics. For example, 2.8 GHz Northwood-core Pentium 4 processors were made in three variants: the Pentium 4/2.8 used a 400 MHz FSB, the Pentium 4/2.8B the 533 MHz FSB, and the Pentium 4/2.8C the 800 MHz FSB. When Intel introduced a 2.8 GHz Pentium 4 based on their new Prescott-core, they designated it the Pentium 4/2.8E.

Interestingly, Intel has also abandoned clock speed as a designator. With the exception of a few older models, all Intel processors are now designated by model number as well. Unlike AMD, whose model numbers retain a vestigial hint at clock speed, Intel model numbers are completely dissociated from clock speeds. For example, the Pentium 4 540 designates a particular processor model that happens to run at 3.2 GHz. The models of that processor that run at 3.4, 3.6, and 3.8 GHz are designated 550, 560, and 570 respectively.

Host-bus speed

The host-bus speed, also called the front-side bus speed, FSB speed, or simply FSB, specifies the data transfer rate between the processor and the chipset. A faster host-bus speed contributes to higher processor performance, even for processors running at the same clock speed. AMD and Intel implement the path between memory and cache differently, but essentially FSB is a number that reflects the maximum possible quantity of data block transfers per second. Given an actual host-bus clock rate of 100 MHz, if data can be transferred four times per clock cycle (thus "quad-pumped"), the effective FSB speed is 400 MHz.

For example, Intel has produced Pentium 4 processors that use host-bus speeds of 400, 533, 800, or 1066 MHz. A 2.8 GHz Pentium 4 with a host-bus speed of 800 MHz is marginally faster than a Pentium 4/2.8 with a 533 MHz host-bus speed, which in turn is marginally faster than a Pentium 4/2.8 with a 400 MHz host-bus speed. One measure that Intel uses to differentiate their lower-priced Celeron processors is a reduced host-bus speed relative to current Pentium 4 models. Celeron models use 400 MHz and 533 MHz host-bus speeds.

All Socket 754 and Socket 939 AMD processors use an 800 MHz host-bus speed. (Actually, like Intel, AMD runs the host bus at 200 MHz, but quad-pumps it to an effective 800 MHz.) Socket A Sempron processors use a 166 MHz host bus, double-pumped to an effective 333 MHz host-bus speed.

Cache size

Processors use two types of cache memory to improve performance by buffering transfers between the processor and relatively slow main memory. The size of Layer 1 cache (L1 cache, also called Level 1 cache), is a feature of the processor architecture that cannot be changed without redesigning the processor. Layer 2 cache (Level 2 cache or L2 cache), though, is external to the processor core, which means that processor makers can produce the same processor with different L2 cache sizes. For example, various models of Pentium 4 processors are available with 512 KB, 1 MB, or 2 MB of L2 cache, and various AMD Sempron models are available with 128 KB, 256 KB, or 512 KB of L2 cache.

For some applications particularly those that operate on small data sets a larger L2 cache noticeably increases processor performance, particularly for Intel models. (AMD processors have a built-in memory controller, which to some extent masks the benefits of a larger L2 cache.) For applications that operate on large data sets, a larger L2 cache provides only marginal benefit.

'''Prescott, the Sad Exception'''

It came as a shock to everyone not the least, Intel to learn when it migrated its Pentium 4 processors from the older 130 nm Northwood core to the newer 90 nm Prescott-core that power consumption and heat production skyrocketed. This occurred because Prescott was not a simple die shrink of Northwood. Instead, Intel completely redesigned the Northwood core, adding features such as SSE3 and making huge changes to the basic architecture. (At the time, we thought those changes were sufficient to merit naming the Prescott-core processor Pentium 5, which Intel did not.) Unfortunately, those dramatic changes in architecture resulted in equally dramatic increases in power consumption and heat production, overwhelming the benefit expected from the reduction in process size.

Process size

Process size, also called fab(rication) size, is specified in nanometers (nm), and defines the size of the smallest individual elements on a processor die. AMD and Intel continually attempt to reduce process size (called a die shrink) to get more processors from each silicon wafer, thereby reducing their costs to produce each processor. Pentium II and early Athlon processors used a 350 or 250 nm process. Pentium III and some Athlon processors used a 180 nm process. Recent AMD and Intel processors use a 130 or 90 nm process, and forthcoming processors will use a 65 nm process.

Process size matters because, all other things being equal, a processor that uses a smaller process size can run faster, use lower voltage, consume less power, and produce less heat. Processors available at any given time often use different fab sizes. For example, at one time Intel sold Pentium 4 processors that used the 180, 130, and 90 nm process sizes, and AMD has simultaneously sold Athlon processors that used the 250, 180, and 130 nm fab sizes. When you choose an upgrade processor, give preference to a processor with a smaller fab size.



Special features

Different processor models support different feature sets, some of which may be important to you and others of no concern. Here are five potentially important features that are available with some, but not all, current processors. All of these features are supported by recent versions of Windows and Linux:



SSE3

SSE3 (Streaming Single-Instruction-Multiple-Data (SIMD) Extensions 3), developed by Intel and now available on most Intel processors and some AMD processors, is an extended instruction set designed to expedite processing of certain types of data commonly encountered in video processing and other multimedia applications. An application that supports SSE3 can run from 10% or 15% to 100% faster on a processor that also supports SSE3 than on one that does not.



64-bit support

Until recently, PC processors all operated with 32-bit internal data paths. In 2004, AMD introduced 64-bit support with their Athlon 64 processors. Officially, AMD calls this feature x86-64, but most people call it AMD64. Critically, AMD64 processors are backward-compatible with 32-bit software, and run that software as efficiently as they run 64-bit software. Intel, who had been championing their own 64-bit architecture, which had only limited 32-bit compatibility, was forced to introduce its own version of x86-64, which it calls EM64T (Extended Memory 64-bit Technology). For now, 64-bit support is unimportant for most people. Microsoft offers a 64-bit version of Windows XP, and most Linux distributions support 64-bit processors, but until 64-bit applications become more common there is little real-world benefit to running a 64-bit processor on a desktop computer. That may change when Microsoft (finally) ships Windows Vista, which will take advantage of 64-bit support, and is likely to spawn many 64-bit applications.



Protected execution

With the Athlon 64, AMD introduced the NX (No eXecute) technology, and Intel soon followed with its XDB (eXecute Disable Bit) technology. NX and XDB serve the same purpose, allowing the processor to determine which memory address ranges are executable and which are non-executable. If code, such as a buffer-over-run exploit, attempts to run in non-executable memory space, the processor returns an error to the operating system. NX and XDB have great potential to reduce the damage caused by viruses, worms, Trojans, and similar exploits, but require an operating system that supports protected execution, such as Windows XP with Service Pack 2.



Power reduction technology

AMD and Intel both offer power reduction technology in some of their processor models. In both cases, technology used in mobile processors has been migrated to desktop processors, whose power consumption and heat production has become problematic. Essentially, these technologies work by reducing the processor speed (and thereby power consumption and heat production) when the processor is idle or lightly loaded. Intel refers to their power reduction technology as EIST (Enhanced Intel Speedstep Technology). The AMD version is called Cool'n'Quiet. Either can make minor but useful reductions in power consumption, heat production, and system noise level.



Dual-core support

By 2005, AMD and Intel were both reaching the practical limits of what was possible with a single processor core. The obvious solution was to put two processor cores in one processor package. Again, AMD led the way with its elegant Athlon 64 X2 series processors, which feature two tightly integrated Athlon 64 cores on one chip. Once again forced to play catch-up, Intel gritted its teeth and slapped together a dual-core processor that it calls Pentium D. The engineered AMD solution has several benefits, including high performance and compatibility with nearly any older Socket 939 motherboard. The slapdash Intel solution, which basically amounted to sticking two Pentium 4 cores on one chip without integrating them, resulted in two compromises. First, Intel dual-core processors are not backward-compatible with earlier motherboards, and so require a new chipset and a new series of motherboards. Second, because Intel more or less simply glued two of their existing cores onto one processor package, power consumption and heat production are extremely high, which means that Intel had to reduce the clock speed of Pentium D processors relative to the fastest single-core Pentium 4 models.

All of that said, the Athlon 64 X2 is by no means a hands-down winner, because Intel was smart enough to price the Pentium D attractively. The least expensive Athlon X2 processors sell for more than twice as much as the least expensive Pentium D processors. Although prices will undoubtedly fall, we don't expect the pricing differential to change much. Intel has production capacity to spare, while AMD is quite limited in its ability to make processors, so it's likely that AMD dual-core processors will be premium priced for the foreseeable future. Unfortunately, that means that dual-core processors are not a reasonable upgrade option for most people. Intel dual-core processors are reasonably priced but require a motherboard replacement. AMD dual-core processors can use an existing Socket 939 motherboard, but the processors themselves are too expensive to be viable candidates for most upgraders.
'''HYPER-THREADING VERSUS DUAL CORE'''

Some Intel processors support ''Hyper-Threading Technology (HTT)'', which allows those processors to execute two program threads simultaneously. Programs that are designed to use HTT may run 10% to 30% faster on an HTT-enabled processor than on a similar non-HTT model. (It's also true that some programs run slower with HTT enabled than with it disabled.) Don't confuse HTT with dual core. An HTT processor has one core that can sometimes run multiple threads; a dual-core processor has two cores, which can always run multiple threads.



Core names and core steppings

The processor core defines the basic processor architecture. A processor sold under a particular name may use any of several cores. For example, the first Intel Pentium 4 processors used the Willamette core. Later Pentium 4 variants have used the Northwood core, Prescott-core, Gallatin core, Prestonia core, and Prescott 2M core. Similarly, various Athlon 64 models have been produced using the Clawhammer core, Sledgehammer core, Newcastle core, Winchester core, Venice core, San Diego core, Manchester core, and Toledo core.

Using a core name is a convenient shorthand way to specify numerous processor characteristics briefly. For example, the Clawhammer core uses the 130 nm process, a 1,024 KB L2 cache, and supports the NX and X86-64 features, but not SSE3 or dual-core operation. Conversely, the Manchester core uses the 90 nm process, a 512 KB L2 cache, and supports the SSE3, X86-64, NX, and dual-core features.

You can think of the processor core name as being similar to a major version number of a software program. Just as software companies frequently release minor updates without changing the major version number, AMD and Intel frequently make minor updates to their cores without changing the core name. These minor changes are called core steppings. It's important to understand the basics of core names, because the core a processor uses may determine its backward compatibility with your motherboard. Steppings are usually less significant, although they're also worth paying attention to. For example, a particular core may be available in B2 and C0 steppings. The later C0 stepping may have bug fixes, run cooler, or provide other benefits relative to the earlier stepping. Core stepping is also critical if you install a second processor on a dual-processor motherboard. (That is, a motherboard with two processor sockets, as opposed to a dual-core processor on a single-socket motherboard.) Never, ever mix cores or steppings on a dual processor motherboard that way lies madness (or perhaps just disaster).

Computer Processor Performance

Processor companies do nothing to discourage longstanding myths about processor performance. It's true that in the early days of microprocessors, a new model was often two or even three times faster than the model it replaced and sold for little or no more. In those halcyon days, the fastest available processors were sometimes 10 times faster than less expensive models that were still being sold.

There was also a favorable bang-for-the-buck ratio. If you paid twice as much for a processor, it was probably considerably more than twice as fast. We remember testing our 4.77 MHz IBM PC/XT against a 16 MHz 286 PC/AT when both were still being sold. The latter system cost two or three times as much, but was something like 10 times faster.

Those days are long past. Nowadays, processor performance increases incrementally, the accompanying price differences are large, the performance gap between the slowest and fastest current models has narrowed substantially, there are many, many more intermediate models available with minor performance differences, and the bang-for-the-buck ratio for the fastest processors has dropped well below 1:1. AMD and Intel have both learned to "work the market," maximizing their revenue in a very competitive market.



Price and Performance

Here's a dirty little secret that AMD and Intel would rather you not know. At any given time, the actual performance differences between their slowest and least expensive "economy" processors and their fastest and most expensive "performance" processors is relatively small. A $750 processor you can buy today will probably be at most 2.5 to 3 times faster than the $50 processor sitting next to it on the store shelf.

Doubling or tripling performance may sound like a huge improvement, but human perception is not linear. A processor must be 30% to 50% faster than another processor before most people perceive any noticeable difference in routine use. Doubling processor speed results in an obvious difference in performance, but not a knock-your-socks-off change. Tripling processor speed provides a very noticeable performance boost, but at a very high price.

And most of that performance increase comes at the lower end of the price continuum. Paying more for a processor yields rapidly diminishing returns. For example, a $175 processor may be twice as fast as a $50 model, or nearly so. Doubling the price to $350 may buy you only a 25% faster processor, and doubling the price again to $700 less than a 10% bump in speed.


ADVICE FROM RON MORSE

Remember, processor speed is only one of the things that determines perceived system performance. Memory speed, bus speed, hard disk performance, and video performance all play a role, albeit to a lesser degree. Still, the fastest processor won't much help a system that's I/O-bound or has a slow video adapter.


But all this is true only for a particular moment in time. As AMD and Intel discontinue older processor models and introduce new ones, the whole continuum of processor performance shifts upward in lockstep. A midrange processor today is faster than the fastest performance processor of a year or 18 months previous, and even today's inexpensive "economy" processor is faster than the fastest processor of 2 to 3 years ago. That's good news, because it means it's often possible to upgrade an older system to today's level of performance at a reasonable low cost.


SOMETIMES EXPENSIVE COSTS LESS

None of this is to say that there's no place for very expensive processors. For programmers who spend their days doing iterative compiles and links, saving just a few seconds on each iteration may well be worth the higher cost of a premium processor. The same is true for highly paid executives, for whom lost seconds translate to lost dollars; for commodity traders, for whom seconds may mean the difference between a huge profit and an equally huge loss; and for serious gamers, who need every advantage they can get (not to mention bragging rights).




AMD versus Intel

Fanboys and brand zealots argue that AMD is faster than Intel, or that Intel is faster than AMD. They're both wrong, and both right. The truth is that at any given price point, Intel and AMD processors are remarkably closely matched in overall performance. That's not to say that their performance is identical for every application. AMD processors, for example, typically have better gaming performance than similarly priced Intel models, and Intel processors typically have better multimedia performance than similarly priced AMD models.


THE PROCESSOR TUG-OF-WAR

For a time, Intel processors badly beat AMD processors by most performance measures. AMD countered this fact by improving their own price/performance ratio, increasing the speed and cache size of their processors, and reducing their prices until they were again competitive with Intel processors that sold for similar prices. Then, for a time, AMD processors badly beat Intel processors by most performance measures. Intel countered this by improving their own price/ performance ratio, increasing the speed and cache size of their processors, and reducing their prices until they were again competitive with AMD processors that sold for similar prices. Each time a gap in price/performance occurs, Intel or AMD adjusts processor pricing and/or performance levels to eliminate that gap. Both companies are smart enough to keep the playing field level while not leaving money on the table.




Benchmarks lie

Benchmarks are supposed to provide neutral measures of the performance of processors, both overall and in terms of specific types of tasks. But modern processors are very complex devices, with numerous strengths and weaknesses relative to competing processor models. A benchmark test that happens to play to a strength of a given processor will make that processor look (unjustifiably) very, very good. Conversely, a benchmark that gives heavy weight to a function that happens to be a weak point of a particular processor will make that processor look very, very bad, again unjustifiably.

If you allow us to choose the benchmark tests, for example, we can "prove" that a $150 AMD processor is faster than a $1,000 Intel processor. But by choosing different benchmark tests, we can just as easily "prove" that a $150 Intel processor is faster than a $1,000 AMD processor.

Broadly speaking, there are two types of benchmarks. Synthetic benchmarks are designed to test individual aspects of a processor's performance, such as cache efficiency, memory throughput, or floating-point performance. Application benchmarks, also called natural benchmarks, incorporate several common applications such as MS Word, Adobe Photoshop, LightWave, and so on with predefined suites of tasks to be performed.

The knock on synthetic benchmarks has always been that they are "meaningless" because they don't measure real-world task performance. We think that's wrong-headed. For example, if we want to decide which processor is likely to be fastest for applications that are bound by memory performance, we can use synthetic benchmarks to test the memory throughput of different processors. The results of those synthetic benchmarks will in fact give us a very good idea of the likely relative performance characteristics of different processors.

Conversely, using application benchmarks provides useful information only if we happen to be running the same applications used in the benchmark suite, in the same way, and with the same relative weighting. Two processors might achieve very similar overall results in an application benchmark, and yet one processor might be a better choice for running one of the suite applications, while the other processor might have the edge for running another.



Optimizing price/performance ratio

Dollar for dollar, AMD and Intel processors typically have very similar overall performance. We follow a few simple rules when we choose a processor, and suggest you do the same:

At the low end, $50 to $125, AMD processors dollar for dollar provide noticeably better performance than Intel processors across the board. Intel has always paid lip service to the low-end market, but it really has no interest in competing here. It costs Intel about $40 to make a processor any processor so it prefers to devote its efforts to market segments with higher profit margins. On the other hand, the low-end market has until recently been AMD's bread and butter, so they devote a lot of attention to this segment.
Choose a low-end processor unless you have a good reason for spending more. For most older systems, the most cost-effective upgrade is a processor that sells for $50 to $75, whether your motherboard is AMD- or Intel-compatible. Low-end processors are perfectly suitable for most computing tasks, including productivity applications, web browsing, email, watching videos, and so on.
In the mainstream range, $125 to $250, Intel and AMD processors are pretty evenly matched dollar for dollar overall. Profit margins are much higher here than in the low-end segment, and unit volumes are huge, so the competition between AMD and Intel here is fierce.
If you put heavier demands on a processor, such as casual video editing or 3D gaming, spending an extra $75 to $125 on your processor upgrade can provide major benefits. Processors in this price range are typically noticeably faster than low-end models, and for some applications that additional performance matters.
At the high end, $250 to $1,000, Intel processors are generally somewhat faster dollar for dollar than AMD processors overall, particularly dual-core models. Although AMD produces the fastest processors in this segment, they set very high prices for those processors compared to Intel models that are only marginally slower, so Intel wins the bang-for-the-buck competition. Profit margins here are very high, but unit volumes are very low, so the actual dollars at stake are much less important than those in the mainstream segment. AMD and Intel compete here mainly for prestige and bragging rights.
Unless the current system is very recent a year old or less it almost never makes sense to upgrade to a high-end processor. The potential incremental performance benefits of a high-end processor, limited as they are under optimum conditions, are even further limited by the low performance of other components in an older system. Furthermore, it's probable that installing a high-end processor would also require that the motherboard, power supply, and possibly the memory be replaced, which amounts to building an entirely new system. The one exception here is devoted gamers, some of whom think nothing of installing a new $1,000 processor every six months (not to mention a new $700 video card, or two.)



Computer Processor Types

A few years ago, choosing a processor was pretty straightforward. AMD and Intel each produced two series of processors, a mainstream line and a budget line. Each company used only one processor socket, and there was a limited range of processor speeds available. If you wanted an Intel processor, you might have a dozen mainstream models and a half-dozen budget models to choose among. The same was true of AMD.


OEM Versus Retail-Boxed

To further confuse matters, most AMD and Intel processors are available in two types of packaging, called OEM and retail-boxed. OEM processor packages include only the bare processor and usually provide only a 90-day warranty. Retail-boxed processors include the processor, a compatible CPU cooler, and a longer warranty, typically three years.

A retail-boxed processor is usually the better deal. It typically costs only a few dollars more than the OEM version of the same processor, and the bundled CPU cooler is usually worth more than the price difference. But if you plan to install an after-market CPU cooler for example, because you are upgrading your system to be as quiet as possible it may make sense to buy the OEM processor.


Nowadays, choosing a processor isn't as simple. AMD and Intel now make literally scores of different processor models. Each company now offers several lines of processors, which differ in clock speed, L2 cache, socket type, host-bus speed, special features supported, and other characteristics. Even the model names are confusing. AMD, for example, has offered at least five different processor models under the same name Athlon 64 3200+. An Intel Celeron model number that ends in J fits Socket 775, and the same model number without the J designates the same processor for Socket 478. A Pentium 4 processor model number that ends in J says nothing about the socket type it is designed for, but indicates that the processor supports the execute-disable bit feature. And so on.

AMD and Intel each offer the three categories of processors described in the following sections.



Budget processors

Budget processors give up a bit of performance in exchange for a lower price. At any given time, AMD or Intel's fastest available budget processor is likely to have about 85% of the performance of their slowest mainstream model. Budget processors are more than sufficient for routine computing tasks. (After all, today's budget processor was yesterday's mainstream processor and last week's performance processor.) Budget processors are often the best choice for a system upgrade, because their lower clock speeds and power consumption make it more likely that they'll be compatible with an older motherboard.



AMD Sempron

The various models of the AMD Sempron processor sell in the $50 to $125 range, and are targeted at the budget through low-end mainstream segment. The Sempron replaced the discontinued Socket A Duron processor in 2004, and the obsolescent Socket A Athlon XP processor in 2005. Various Sempron models are available in the obsolescent Socket A and in the same Socket 754 used by some Athlon 64 models.

AMD actually packages two different processors under the Sempron name. A Socket A Sempron, also called a K7 Sempron, is in fact a re-badged Athlon XP processor. A Socket 754 Sempron, shown in Figure 5-1 is also called a K8 Sempron, and is really a cut-down Athlon 64 model running at a lower clock speed with a smaller L2 cache and a single-channel memory controller rather than the dual-channel memory controller of the Athlon 64. Early Sempron models had no support for 64-bit processing. Recent Sempron models include 64-bit support, although the practicality of running 64bit software on a Sempron is questionable. Still, like the Athlon 64, the Sempron also runs 32-bit software very efficiently, so you can think of the 64-bit support as future-proofing.





If you have a Socket 462 (A) or Socket 754 motherboard in your system, the Sempron offers an excellent upgrade path. You'll need to verify compatibility of your motherboard with the specific Sempron you intend to install, and you may need to upgrade the BIOS to recognize the Sempron.

For more information about Sempron processor models, visit 

http://www.amd.com/sempron.

Intel Celeron

For many years, the Intel Celeron processor was the poor stepsister, offering too little performance at too high a price. Cynical observers believed that the only reason Intel sold any Celeron processors at all was that system makers wanted the Intel name on their boxes without having to pay the higher price for an Intel mainstream processor.

That all changed when Intel introduced their Celeron D models, which are now available for Socket 478 and Socket 775 motherboards. While Celeron D models are still slower than Semprons dollar-for-dollar, the disparity is nowhere near as large as in years past. Celeron D processors, which sell in the $60 to $125 range, are very credible upgrade processors for anyone who owns a Socket 478 or Socket 775 motherboard. Like the Sempron, Celeron models are available with 64-bit support, although again the practicality of running 64-bit software on an entry-level processor is questionable. Once again, it's important to verify the compatibility of your motherboard with the specific Celeron you intend to install, and you may need to upgrade the BIOS to recognize the Celeron.


AVOID NON-D CELERON PROCESSORS

Celeron processors (without the "D") are based on the Northwood core and have only 128 KB of L2 cache. These processors have very poor performance, and unfortunately remain available for sale. The Celeron D models are based on the Prescott-core, and have 256 KB of L2 cache.


For more information about Celeron processor models, visit http://www.intel.com/celeron.



Mainstream processors

Mainstream processors typically cost $125 to $250 although the fastest models sell for $500 or more and offer anything up to about twice the overall performance of the slowest budget processors. A mainstream processor may be a good upgrade choice if you need more performance than a budget processor offers and are willing to pay the additional cost.

However, depending on your motherboard, a mainstream processor may not be an option even if you are willing to pay the extra cost. Mainstream processors consume considerably more power than most budget processors, often too much to be used on older motherboards. Also, mainstream processors often use more recent cores, larger L2 caches, and other features that may or may not be compatible with an older motherboard. An older power supply may not provide enough power for a current mainstream processor, and the new processor may require faster memory than is currently installed. If you intend to upgrade to a mainstream processor, carefully verify compatibility of the processor, motherboard, power supply, and memory before you buy the processor.



AMD Athlon 64

The AMD Athlon 64 processor, shown in Figure 5-2, is available in Socket 754 and Socket 939 variants. As its name indicates, the Athlon 64 supports 64-bit software, although only a tiny percentage of Athlon 64 owners run 64-bit software. Fortunately, the Athlon 64 is equally at home running the 32-bit operating systems and applications software that most of us use.





Like the Sempron, the Athlon 64 has a memory controller built onto the processor die, rather than depending on a memory controller that's part of the chipset. The upside of this design decision is that Athlon 64 memory performance is excellent. The downside is that supporting a new type of memory, such as DDR2, requires a processor redesign. Socket 754 models have a single-channel PC3200 DDR-SDRAM memory controller versus the dual-channel controller in Socket 939 models, so Socket 939 models running at the same clock speed and with the same size L2 cache offer somewhat higher performance. For example, AMD designates a Socket 754 Newcastle-core Athlon 64 with 512 KB of L2 cache running at 2.2 GHz a 3200+ model, while the same processor in Socket 939 is designated an Athlon 64 3400+.


NUMBERS LIE

The model numbers of Athlon 64 and Sempron processors are scaled differently. For example, the Socket 754 Sempron 3100+ runs at 1800 MHz and has 256 KB of cache, and the Socket 754 Athlon 64 2800+ runs at the same clock speed and has twice as much cache. Despite the lower model number, the Athlon 64 2800+ is somewhat faster than the Sempron 3100+. Although AMD hotly denies it, most industry observers believe that AMD intends Athlon 64 model numbers to be compared with Pentium 4 clock speeds and Sempron model numbers with Celeron clock speeds. Of course, Intel also designates their recent processors by model number rather than clock speed, confusing matters even further.


For more information about Athlon 64 processor models, visit http://www.amd.com/athlon64.

Intel Pentium 4

The Pentium 4, shown in Figure 5-3, is Intel's flagship processor, and is available in Socket 478 and Socket 775. Unlike AMD which sometimes uses the same Athlon 64 model number to designate four or more different processors with different clock speeds, L2 cache sizes, and sockets Intel uses a numbering scheme that identifies each model unambiguously.

Older Pentium 4 models, which are available only in Socket 478, are identified by clock speed and sometimes a supplemental letter to indicate FSB speed and/or core type. For example, a Socket 478 Northwood-core Pentium 4 processor operating at a core speed of 2.8 GHz with the 400 MHz FSB is designated a Pentium 4/2.8. The same processor with the 533 MHz FSB is designated a Pentium 4/2.8B, and with the 800 MHz FSB it's designated a Pentium 4/2.8C. A 2.8 GHz Prescott-core Pentium 4 processor is designated a Pentium 4/2.8E.



Socket 775 Pentium 4 models belong to one of two series. All 500-series processors use the Prescott-core and have 1 MB of L2 cache. All 600-series processors use the Prescott 2M core and have 2 MB of L2 cache. Intel uses the second number of the model number to indicate relative clock speed. For example, a Pentium 4/530 has a clock speed of 3 GHz, as does a Pentium 4/630. The 540/640 models run at 3.2 GHz, the 550/650 models at 3.4 GHz, the 560/660 models at 3.6 GHz, and so on. A "J" following a 500-series model number (for example, 560J) indicates that the processor supports the XDB feature, but not EM64T 64-bit support. If a 500-series model number ends in 1 (for example, 571) that model supports both the XDB feature and EM64T 64-bit processing. All 600-series processors support both XDB and EM64T.

For more information about Pentium 4 processor models, visithttp://www.intel.com/pentium4.


Extreme Processors

We classify the fastest, most expensive mainstream processors those that sell in the $400 to $500 range as performance processors, but AMD and Intel reserve that category for their top-of-the-line models, which sell for $800 to $1,200. These processors the AMD Athlon 64 FX, the Intel Pentium 4 Extreme Edition, and the Intel Pentium Extreme Edition are targeted at the gaming and enthusiast market, and offer at best marginally faster performance than the fastest mainstream models.

In fact, the performance bump is generally so small that we think anyone who buys one of these processors has more dollars than sense. If you're considering buying one of these outrageously expensive processors, do yourself a favor. Buy a $400 or $500 high-end mainstream processor instead, and use part of the extra money for more memory, a better video card, a better display, better speakers, or some other component that will actually provide a noticeable benefit. Either that, or keep the extra money in the bank.




Dual-core processors

By early 2005, AMD and Intel had both pushed their processor cores to about the fastest possible speeds, and it had become clear that the only practical way to increase processor performance significantly was to use two processors. Although it's possible to build systems with two physical processors, doing that introduces many complexities, not least a doubling of the already-high power consumption and heat production. AMD, later followed by Intel, chose to go dual-core.

Combining two cores in one processor isn't exactly the same thing as doubling the speed of one processor. For one thing, there is overhead involved in managing the two cores that doesn't exist for a single processor. Also, in a single-tasking environment, a program thread runs no faster on a dual-core processor than it would on a single-core processor, so doubling the number of cores by no means doubles application performance. But in a multitasking environment, where many programs and their threads are competing for processor time, the availability of a second processor core means that one thread can run on one core while a second thread runs on the second core.

The upshot is that a dual-core processor typically provides 25% to 75% higher performance than a similar single-core processor if you multitask heavily. Dual-core performance for a single application is essentially unchanged unless the application is designed to support threading, which many processor-intensive applications are. (For example, a web browser uses threading to keep the user interface responsive even when it's performing a network operation.) Even if you were running only unthreaded applications, though, you'd see some performance benefit from a dual-core processor. This is true because an operating system, such as Windows XP, that supports dual-core processors automatically allocates different processes to each core.



AMD Athlon 64 X2

The AMD Athlon 64 X2, shown in Figure 5-4, has several things going for it, including high performance, relatively low power requirements and heat production, and compatibility with most existing Socket 939 motherboards. Alas, while Intel has priced its least expensive dual-core processors in the sub-$250 range, the least expensive AMD dual-core models initially sold in the $800 range, which is out of the question for most upgraders. Fortunately, by late 2005 AMD had begun to ship more reasonably priced dual-core models, although availability is limited.





For more information about Athlon 64 X2 processor models, visit http://www.amd.com/athlon64.



Intel Pentium D

The announcement of AMD's Athlon 64 X2 dual-core processor caught Intel unprepared. Under the gun, Intel took a cruder approach to making a dual-core processor. Rather than build an integrated dual-core processor as AMD had with its Athlon 64 X2 processors, Intel essentially slapped two slower Pentium 4 cores on one substrate and called it the Pentium Ddual-core processor.

The 800-series 90 nm Smithfield-core Pentium D, shown in Figure 5-5, is a stop-gap kludge for Intel, designed to counter the AMD Athlon 64 X2 until Intel can bring to market its real answer, the dual-core 65 nm Presler-core processor, which is likely to be designated the 900-series Pentium D. The Presler-based dual-core processors will be fully integrated, compatible with existing dual-core Intel-compatible motherboards, and feature reduced power consumption, lower heat output, twice as much L2 cache, and considerably higher performance.





Reading the foregoing, you might think we had only contempt for the 800-series Pentium D processors. In fact, nothing could be further from the truth. They're a kludge, yes, but they're a reasonably cheap, very effective kludge, assuming that you have a motherboard that supports them. We extensively tested an early sample of the least expensive 800-series Pentium D, the 820. The 820 runs at 2.8 GHz, and under light, mostly single-tasking use, the 820 "feels" pretty much like a 2.8 GHz Prescott-core Pentium 4. As we added more and more processes, the difference became clear. Instead of bogging down, as the single-core Prescott would have done, the Pentium D provided snappy response to the foreground process.

For more information about Pentium D processor models, visit http://www.intel.com/products/processor/....



AMD and Intel processor summaries

Table 5-2 lists the important characteristics of current AMD processors, including the special features they support.





Table 5-3 lists the important characteristics of current Intel processors, including the special features they support.













SPECIAL FEATURESSpecial features are not always implemented across an entire line of processors.

 For example, we list the Pentium D 8XX-series processors as supporting EM64T,

 SSE3, EIST, and dual core. At the time we wrote this, three Pentium D 8XX models

 were available: the 2.8 GHz 820, the 3.0 GHz 830, and the 3.2 GHz 840. The 830 

and 840 models support all of the special features listed. The 820 model supports

 EM64T, SSE3, and dual-core operation, but not EIST. If a special feature listed

 as being supported by a particular line of processors is important to you, verify

 that it is supported in the exact processor model you intend to buy.


Computer CPU Coolers

Modern CPUs consume a lot of power as much as 130W. That power ends up as waste heat. In effect, a modern system has the equivalent of a 50W to 130W incandescent lightbulb burning constantly inside the case. That analogy understates the problem a lightbulb dissipates its heat from the relatively large surface of the bulb. A processor must dissipate the same amount of heat over the much smaller surface area of the processor die, typically about 0.25 square inch. Without an effective heatsink to draw away this heat, the processor might literally burn itself to a crisp almost instantly.

Nearly all systems deal with this heat problem by placing a massive metal heatsink in close contact with the processor die (or integrated heat spreader) and using a small fan to draw or push air through the heat-sink fins. This device is called a heat-sink/fan (HSF) or CPU cooler. As the power consumption of processors has continued growing, so too has the size and mass of the heatsinks they use. Even the stock coolers packaged with retail-boxed processors nowadays are often quite large and heavy. For example, Figure 5-6 shows a stock Intel Pentium 4 CPU cooler on the left and a Thermalright XP-120 aftermarket CPU cooler on the right, with a pair of AA batteries shown for scale.








CPU Cooler Plumbing

Those things that look like pipes on the Thermalright XP-120 cooler are pipes. Heat pipes, to be exact. Some high-end CPU coolers, including this model, use heat pipes to increase cooling efficiency. Heat pipes operate much like your refrigerator. The heat generated by the processor vaporizes a fluid. The resulting gas rises by convection up the heat pipe to the radiator section at the top of the cooler, where it condenses, giving up its heat to the radiator.

Unlike stock coolers, some aftermarket coolers including this Thermalright model do not include a bundled fan. That's because such coolers tend to be used by performance-and silent-PC enthusiasts, who prefer to choose a fan with particular airflow and noise characteristics. This Thermalright cooler can use a large (120 mm) fan, which because of its size can run relatively slowly (and silently) while still providing a sufficient volume of air flow to cool the processor effectively. In fact, because of their large surface area and high efficiency, some high-performance aftermarket coolers, including the XP-120, can cool all but the fastest, hottest processors without using a CPU fan. The airflow from a case fan suffices to remove waste heat from the cooler.



JUST BECAUSE IT FITS

Do not assume that merely because a heatsink fits a processor, it is sufficient to cool that processor. Faster processors are physically identical to slower models, but produce more heat. Heatsinks are rated by processor speed. For example, a heatsink rated for a 2.4 GHz Pentium 4 can physically be installed on a 3.8 GHz Pentium 4, but is grossly inadequate to cool it. Nor can you judge solely by processor speed. For example, Intel has produced 2.8 GHz Pentium 4 processors using the earlier, cooler-running Northwood core and the later, hotter-running Prescott-core. A heatsink rated for use with a 2.8 GHz Northwood-core Pentium 4 is not good enough for a 2.8 GHz Prescott-core Pentium 4. Make sure that the heatsink/fan unit you choose is rated for the specific processor you use it with.


Heatsinks are constructed with different materials, according to their prices and intended uses. An inexpensive heatsink, or one intended for use with a slower processor, is likely to be of all-aluminum construction. Aluminum is inexpensive and relatively efficient in transferring heat. Copper is much more expensive than aluminum, but is also much more efficient in transferring heat. Accordingly, a more expensive heatsink, or one intended for a faster processor, might be constructed primarily of aluminum, but with copper surfaces where the processor contacts the heatsink. The most expensive heatsinks, and those intended for use with the fastest processors, are constructed of pure copper.

Heatsink/fan units also differ in the type and size of fan they use, and how fast that fan runs. Fan speed is an issue, because all other things being equal, a faster-running fan produces more noise. For equal air flow, a larger, slower fan produces less noise than a smaller, faster fan. Fan sizes have increased as processor speeds have increased, to provide the high air flow volume needed to cool the heatsink while keeping fan speed (and noise) at a reasonable level. For example, heatsinks for Pentium II processors used 30 mm fans. Heatsinks for early Pentium 4 and Athlon 64 processors typically used 60 mm or 70 mm fans. Some third-party "performance" heatsinks targeted at overclockers use 80 mm, 92 mm, or 120 mm fans. Some even use multiple fans.

In general, we recommend using the CPU coolers that are bundled with retail-boxed processors. The bundled coolers are generally midrange in terms of performance and noise level neither as efficient nor as quiet as good aftermarket coolers, but less costly.

However, if you are concerned about PC noise, a third-party CPU cooler is the way to go. You can spend anything from about $15 to more than $100 on a quiet CPU cooler, depending on the processor you're using and just how quiet and efficient you require the cooler to be. Arctic Cooling (http://www.arctic-cooling.com) makes several models in the $15 to $30 range that are reasonably quiet and efficient. If you're willing to spend a bit more, look at Zalman 7000- and 7700-series coolers (http://www.zalmanusa.com), which are in the $30 to $45 range, and are extremely quiet and so efficient that some models can be run fanless (and therefore completely silent) with some processors. Finally, if only the best will do and you're willing to pay $60 or more for a CPU cooler, choose a Thermalright (http://www.thermalright.com) model and add one of the fans recommended by Thermalright.


Thermal Compound Is Critical

The best heatsink/fan can't cool a processor properly unless thermal compound is used at the processor/heatsink interface. The processor and heatsink base are both flat and polished, but even when they are pressed into close contact, a thin layer of air separates them. Air insulates well, which is the last thing you want, so thermal compound is used to displace the air.

When you install a heatsink, and each time you remove and replace it, use fresh thermal compound to ensure proper heat transfer. Thermal compound is available in the form of viscous thermal "goop" and as phase-change thermal pads, which melt as the processor heats up and solidify as it cools down. Make sure that the thermal compound you use is approved by the processor maker. For example, AMD specifies particular phase-change thermal pads for certain of its processors, and warns that using any other thermal compound voids the warranty.



USE WHAT IT CAME WITH

We generally use the thermal compound or phase-change medium that is provided with the cooler. (AMD in particular is very specific about which thermal transfer media are acceptable for its processors.) When we reinstall a cooler, we generally use Antec Silver Thermal Compound (http://www.antec.com), which is inexpensive and as good as or better than anything else we've used.



The Wrong CPU Cooler Can Kill Your Motherboard

Choosing the best aftermarket HSF is not trivial. Verifying that the cooler is rated for your processor is just the first step. Specialty coolers those that provide high cooling efficiency or low noise levels, or both are typically large and heavy (and expensive).

Size is important because the space around the processor socket is often cluttered with capacitors and other components that may prevent a large cooler from being seated properly. More than one system builder has learned to his dismay that a cooler that appears to fit may upon being clamped down bend, damage, or short out nearby components. We have never understood why most third-party CPU cooler makers don't provide motherboard compatibility lists ( Zalman, for one, does). In the absence of such lists, the best way to avoid damaging your motherboard is to verify visually that all components will clear the cooler before you clamp it into place. If it doesn't fit well, that's another good argument for buying from vendors that have good return policies.

Weight is important because Intel and AMD specify maximum heatsink weights for which the retaining brackets for their various processors are rated. Many specialty CPU coolers exceed the maximum allowable weight sometimes by large margins which introduces the ugly possibility of the cooler breaking free from its mount and rattling around loose inside the case. This is an issue with any tower system or other PC that mounts the motherboard vertically, and is a particular danger with portable systems, such as LAN party PCs. AMD Socket A systems are particularly prone to this problem, because the cooler clamps to the CPU socket directly rather than to a retaining bracket that is secured to the motherboard.

The best solution, if you must use such a heavy cooler, is to choose one that comes with a custom retaining bracket rather than depending on the standard motherboard bracket. It's also a good idea to transport such systems in a motherboard horizontal orientation to reduce the risk of breakage during transit.



Computer CPU Upgrades

Replacing the processor with a faster model is one of the most effective and cost-efficient upgrades you can make on an older system. In some cases, you can double or triple CPU performance at a relatively small cost. Unfortunately, not all systems are good candidates for a processor upgrade. You'll have to do a bit of research to determine whether your system is suitable for a processor upgrade. Here are the factors to consider:



Processor socket type

The first consideration is the socket type provided by the motherboard. Motherboards that use a current socket Socket 775 for Intel or Socket 939 for AMD are the best upgrade candidates. Motherboards that use older sockets Sockets 462 (A) or 754 for AMD or Socket 478 for Intel offer fewer processor choices, but are still reasonable upgrade candidates. Motherboards that use very old sockets, such as Intel Socket 370, are poor upgrade candidates, because few processors are still available for them. Motherboards that use obsolete sockets Socket 7 and earlier, Slot A, or Slot 1 are not realistically upgradable. Even if you can find the components you need to upgrade these obsolete systems, the price will be high, and even after the upgrade, the system will be too slow to be useful.


What About Socket Adapters?

Evergreen Technologies and other companies manufacture adapters that allow you to install a processor that uses a different socket than the motherboard, such as a Socket 478 processor in a Socket 423 motherboard. Such adapters have been around for years. For example, in the late 90s, "slocket" adapters allowed Socket 370 Pentium III processors to be installed in Slot 1 motherboards.

These adapters have never been very satisfactory. Sometimes they work, more or less, but they introduce many compatibility issues. They are also generally quite costly. You can usually replace the motherboard for about the same total cost. Replacing the motherboard gives you a newer chipset and BIOS, and, of course, a new motherboard rather than one that's several years old. We suggest you avoid such socket adapters.




Motherboard model and revision level

Just because a motherboard has the proper socket doesn't mean it can necessarily accept any processor that uses that socket. Before you begin an upgrade, verify the compatibility of your motherboard with the upgrade processor you are considering. (See Computer Motherboards.)



BIOS

Quite often, a motherboard can support a much faster processor than is currently installed, but requires a BIOS update to do so. Before you start an upgrade, check the web site for the motherboard to find the latest BIOS update available for that motherboard. Check the BIOS release notes to determine whether that BIOS version supports the processor you plan to install.


YOU CAN'T GET THERE FROM HERE

Install the BIOS update before you remove the old processor. Otherwise, you may not be able to install the BIOS update because the new processor won't boot with the older BIOS.



Upgrading Consumer-Grade PCs

Mass-market, consumer-grade PCs sold online and in big-box stores are generally poor candidates for processor upgrades. That's no accident. Mass-market PC vendors don't want you to upgrade your PC. They want you to buy a new one.

Accordingly, they take steps to make it difficult or impossible to upgrade the systems they build. One common practice is to use a modified BIOS that supports only a limited range of processor speeds or bus speeds, even if the motherboard itself is capable of using faster processors. Another is to conceal the actual manufacturer and model number of the motherboard, and to refuse to provide the technical documentation needed by upgraders.

Quite often, the only way to upgrade the processor in a mass-market, consumer-grade system is to replace the motherboard at the same time. In fact, some manufacturers have gone to extremes to prevent users from upgrading their systems. Dell for a time used nonstandard power supplies, which meant that the Dell power supply would destroy a standard motherboard and a standard power supply would destroy a Dell motherboard. Fortunately, most of those systems are now so old that they're not economically upgradable anyway, but it's still a good idea to keep an eye out for intentional incompatibilities. Once again, Google is your friend. Before you upgrade a PC, search Google to learn about any possible gotchas.




CPU cooler

Installing a new processor usually requires installing a new CPU cooler. The old cooler may fit the new processor, but chances are good that it's not good enough to cool the faster new processor. Buy a retail-boxed processor, which comes with a stock CPU cooler, or choose an appropriate aftermarket CPU cooler, as described in the preceding section.



Memory

If you have current PC3200 or DDR2 memory installed, the new processor will probably operate properly with it. If you have slower memory installed, such as PC1600, PC2100, or PC2700 DDR-SDRAM, you may need to replace the memory as well as the processor. Some motherboards support asynchronous memory operation, which is to say that they can run memory at a slower speed than the processor memory bus. Even if you have such a motherboard, though, using slower memory than the processor was designed to use reduces processor performance, which was the whole reason for upgrading the processor.



Power supply

The power supply in many older systems particularly mass-market, consumer-grade systems is barely adequate to run the components that were originally installed. Faster processors usually consume more power, so it's quite possible that installing a faster processor will also require installing a higher-capacity power supply. Whether to replace the power supply as a part of the upgrade is a judgment call. If the current power supply is a good brand and of reasonably high capacity, and if the new processor doesn't consume much more wattage than the original, it's probably safe to continue using the old power supply. On the other hand, if the system refuses to boot or crashes frequently after the processor upgrade, that's a good sign that the power supply needs to be replaced.



Identifying the current processor

It's sometimes important to identify an unknown CPU, or at least one for which you don't know all the details. If the CPU is not installed, you can identify it unambiguously by examining the markings on its surface and comparing those markings to identification information published on the manufacturer's web site. For example, Figure 5-7 shows the processor markings that Intel uses to identify Socket 775 Pentium D and Pentium Extreme Edition processors. AMD uses similar markings and publishes them on its web site.





More often, you'll need to identify an Figure 5-7. Intel Pentium D processor markings (image courtesy of Intel Corporation) installed processor. The easiest way to do that is to use Everest Home Edition, SiSoft Sandra, or a similar general diagnostics utility. Figure 5-8shows Everest Home Edition identifying an installed processor as an AMD Sempron 2800+. In addition to the processor name and model, these utilities provide other potentially important information, such as the CPU core name and stepping, the cache size, and the package type.








Choosing a replacement processor

Socket type, motherboard compatibility, and other factors limit the range of suitable upgrade processors. Even with those limitations, though, you'll likely have at least several and possibly dozens of processors to choose among. Use the following guidelines to make the best choice:



Consider total cost versus system value.

If you can simply drop a $50 processor into an old system without any other upgrades, that's one thing. If you'll also need to upgrade the memory, power supply, and/or other system components, you may be better off simply retiring the old system to less-demanding duties and building an entirely new system. (See our book Building the Perfect PC, O'Reilly 2004.) Conversely, if you're upgrading a more recent system, it may make sense to spend more money on the upgrade to bring that system up to current performance levels.



Consider bang for the buck.

For example, you may have a choice of several Sempron or Celeron models ranging in price from $60 to $130. If even the slowest and least expensive of those processors represents a significant performance upgrade over the original processor, it probably makes little sense to buy anything more than the slowest upgrade model. Paying more will buy you little additional performance.



Consider power consumption.

The smaller the differential between the power consumption of the old and new processors, the easier the upgrade. For example, if you're upgrading a Socket 754 motherboard, you may have a choice between a 62W Sempron and a 110W Athlon 64. As attractive as the higher performance of the Athlon 64 is, using it may introduce cooling and power supply issues.



CPU Replacement

The exact steps required to replace a processor depend on many factors, including the type of processor, CPU cooler, motherboard, and case you are using. In the following sections, we illustrate the procedure for replacing a Socket 478 processor. Most other processors, including Socket 462 (A), Socket 754, and Socket 939 models, require similar steps. Socket 775 processors differ significantly, so we illustrate the installation of a Socket 775 processor separately.


Cleanliness Is Next to GoodlinessOne of our tech reviewers suggests precleaning the system in a less dirt-sensitive location, such as a garage workbench, prior to moving the computer onto the kitchen table for the balance of the process. This precaution enhances domestic bliss and increases the possibility of budget increases when it comes time for the next upgrade.



A NASTY CRACKIf you decide to install the processor with the motherboard in place, be very careful about how much pressure you apply when installing the new CPU cooler. Applying too much pressure when you install the CPU cooler can crack the motherboard.




Removing the old processor

The first step in replacing the processor is to remove the old processor. To do so, take the following steps:

Disconnect the power cord, monitor, keyboard, mouse, and other external peripherals, and move the system to a well-lit work area. Again, the kitchen table is traditional. Remove the cover from the case and clean the system thoroughly, inside and out. There are few things less pleasant than working on a filthy system.
Examine the system to decide whether to remove the motherboard before proceeding or to install the new processor with the motherboard in place. That decision depends on many factors, including your level of experience in replacing processors, the amount of working room available inside the case, the type of clamping mechanism used to secure the CPU cooler, and so on. If in doubt, remove the motherboard.
If you elect to remove the motherboard, record the locations of every cable that connects to it. Many people use a digital camera for that purpose. Disconnect all of the cables and remove the screws that secure the motherboard to the case. Ground yourself by touching the case structure or the power supply, lift the motherboard out of the case, and place it on a flat, nonconductive surface.
If you haven't done so already, remove the cable that connects the CPU cooler fan to the motherboard power header. Release the clamp or clamps that secure the CPU cooler to the motherboard, and attempt to lift the CPU cooler away from the motherboard, using very gentle pressure. If necessary, you can slide the CPU cooler back and forth very gently in the horizontal plane, keeping its base parallel to the motherboard.
Set the original CPU cooler aside. If you plan to salvage it and the original processor (why not?), remove the remnants of the thermal compound from the base of the cooler. You can often do so just by rubbing the base with your thumb to remove the compound, which usually has the consistency of rubber cement. If the thermal compound is too persistent, try using the edge of a credit card or a knife to scrape off the compound. Be careful to avoid scratching the surface of the cooler. Goof-Off or a similar solvent may also be helpful. Some people even use fine steel wool, but if you do that, make sure that no small pieces remain on the cooler. If you use the cooler later, even a tiny piece of steel wool can short out the processor or the motherboard, causing all sorts of problems.
With the CPU cooler removed, the processor is visible in its socket. If you intend to salvage the processor for later use, it's a good idea to remove the remnants of the thermal compound while the CPU is still seated in the socket, where it is well grounded and protected from injury. You can do so by rubbing gently with your thumb or by using the edge of a credit card as a scraper. Once again, use a hair dryer to warm the processor if you have difficulty removing the thermal compound.
Once the processor is clean, lift the ZIF lever to release the clamping pressure on the socket and then lift the processor from the socket. It should separate from the socket without any resistance at all. If it does not, you can apply gentle pressure to separate it, but be very careful not to bend (or snap off) any of the fragile processor pins. Even if you don't plan to reuse the processor, a snapped-off pin may render the motherboard useless.
For the time being, place the processor pins-up on a flat, nonconductive surface such as the tabletop. Later on, you can use the packaging from the new processor to store the old processor.



GENTLE PERSUASIONIf the CPU cooler doesn't break loose with gentle persuasion, don't yank it. The thermal compound between the CPU cooler and the CPU sometimes sets up like glue. Pulling too hard can pull the CPU right out of the socket, damaging the old CPU and possibly the socket. If that happens, you may have to replace the motherboard.If you're working with the motherboard in situ, turn the computer on and let it run for a few minutes to warm the processor, which melts the thermal compound and makes it easier to break the bond. If you've removed the motherboard, point a hair dryer at the CPU cooler and CPU and let it run for several minutes, until the CPU cooler becomes warm to the touch. At that point, the CPU cooler should separate easily from the CPU.




Installing the new processor (Sockets 462/A, 478, 754, 939)

The exact procedure needed to install a processor varies slightly for different processors and CPU coolers, but the general procedure is similar. In this section, we illustrate the procedure for installing a Socket 478 Pentium 4 processor, but the procedure is identical for a Celeron, and nearly so for Socket 462 (A), Socket 754, and Socket 939 Athlon 64 and Sempron processors. The only real difference is how the CPU cooler is secured, and that should be obvious to you when you examine your particular CPU cooler.


SOMEONE ALWAYS HAS TO BE DIFFERENT

Socket 775 Intel processors use a slightly different procedure. Rather than being secured with a ZIF lever that clamps the processor pins, Socket 775 processors seat loosely in the socket and are secured by clamping the processor body with a retaining mechanism that is part of the socket. See the following section for details.


We chose a retail-boxed processor to illustrate this section. One advantage of a retail-boxed processor is that it comes with a competent CPU cooler that is guaranteed to be compatible with the processor, and typically costs only a few dollars more than the bare OEM processor. The CPU coolers that Intel and AMD currently bundle with their retail-boxed processors are quite good, especially considering the low incremental cost of buying the bundle. The bundled coolers aren't quite as efficient or as quiet as the best aftermarket CPU coolers, but they suffice for most purposes.

Our retail-boxed Pentium 4 processor, shown in Figure 5-9, includes the processor itself and a large Intel-branded CPU cooler. The plastic packaging Intel uses is treacherous. We eventually got the package open using scissors, but for a time we thought we'd have to resort to a chain saw.






OPEN SESAME

Don't try to pry the package open using just your fingers. Robert did that once with an Intel retail-boxed processor. When the package finally popped, the heat-sink/fan unit went sailing across the room and the processor landed in his lap. (Thank goodness it wasn't the converse. ) AMD packaging is also obnoxious, but not as bad as Intel packaging.


The first step is to lift the arm of the ZIF (zero insertion force) socket, as shown in Figure 5-10, until it is vertical. With the arm vertical, there is no clamping force on the socket holes, which allows the processor to drop into place without requiring any pressure.








Zero Means Zero

Never apply pressure to seat the processor. You'll bend the pins and destroy the processor. Note that closing the ZIF lever may cause the processor to rise up slightly from the socket. If this happens, raise the lever again and reseat the processor. After the processor is fully seated, it's safe to apply gentle pressure with your finger to keep it in place as you close the ZIF lever.


Correct orientation is indicated on the processor and socket by some obvious means. For Socket 478, the processor has a trimmed corner and the socket a small triangle, both visible in Figure 5-11 near the ZIF socket lever. With the socket lever vertical, align the processor with the socket and drop the processor into place, as shown in Figure 5-11. The processor should seat flush with the socket just from the force of gravity, or with at most a tiny push. If the processor doesn't simply drop into place, something is misaligned. Remove the processor and verify that it is aligned properly and that the pattern of pins on the processor corresponds to the pattern of holes on the socket.







With the processor in place and seated flush with the socket, press the lever arm down and snap it into place, as shown in Figure 5-12. You may have to Cleanliness Counts press the lever arm slightly away from the socket to allow it to snap into a locked position.








Cleanliness Counts

If the processor has previously been used, clean off any remaining thermal compound or the remnants of the thermal pad before you install the heatsink/fan unit. You can remove old thermal compound using Goof-Off or isopropyl alcohol on a cloth, or by polishing the processor gently with 0000 steel wool. If you use steel wool, which is conductive, make absolutely sure that no stray bits of it remain after you finish polishing the processor. Even a tiny piece of steel wool can short out the processor or another motherboard component, with disastrous results. Better yet, use steel wool only when the processor is away from the motherboard, prior to installation.


To install the CPU cooler, begin by polishing the top of the processor with a paper towel or soft cloth, as shown in Figure 5-13. (Our editor, Brian Jepson, notes that he's become fond of coffee filters, as they are abrasive enough to polish, and so far haven't scratched anything. Plus, they don't seem to leave any debris.) Remove any grease, grit, or other material that might prevent the heatsink from making intimate contact with the processor surface.







Next, check the contact surface of the heatsink, shown in Figure 5-14. If the heatsink base is bare, that means it's intended to be used with thermal compound, usually called "thermal goop." In that case, also polish the heatsink base.







Some heatsinks have a square or rectangular pad made of a phase-change medium, which is a fancy term for a material that melts as the CPU heats and solidifies as the CPU cools. This liquid/solid cycle ensures that the processor die maintains good thermal contact with the heatsink. If your heatsink includes such a pad, you needn't polish the base of the heatsink. (Heatsinks use either a thermal pad or thermal goop, not both.)


ALUMINUM VERSUS COPPER

The heatsink shown in Figure 5-14 is a so-called "AlCu" hybrid unit, for the chemical symbols for aluminum and copper. The body of the heatsink is made from aluminum, and the contact surface for the processor from copper. Copper has better thermal properties, but is much more costly than aluminum.

Inexpensive heatsinks and those designed for slower, cooler-running processors use aluminum exclusively. Heatsinks designed for fast, hot-running processors (and for overclockers) use copper exclusively. Hybrid heatsinks balance cost and performance by using copper only where heat transfer properties are critical.



Different Goops

Don't worry if your heatsink or thermal compound differs from those in the illustrations. The type of heatsink and thermal compound supplied with retail-boxed processors varies from model to model and may also vary within a model line.

When we replace a heatsink, we use Antec Silver Thermal Compound, which is widely available, inexpensive, and works well. Don't pay extra for "premium" brand names like Arctic Silver. They cost more than the Antec product and our testing shows little or no difference in cooling efficiency.


Intel never uses a cheap method when a better solution is available, and the packaging for their thermal compound is no exception. Rather than the usual single-serving plastic packet of thermal goop, Intel provides thermal goop in a syringe with a premeasured dose. To apply the thermal goop, put the syringe tip near the center of the processor and squeeze the entire contents of the syringe onto the processor surface, as shown in Figure 5-15.






Too Much Is as Bad as Too Little

Incidentally, the premeasured thermal goop syringe shown here illustrates the proper amount of goop for any modern AMD or Intel processor. If you're applying goop from a bulk syringe, squeeze out only the amount shown here, about 0.1 milliliter (mL), which may also be referred to as 0.1 cubic centimeter (CC). Most people tend to use too much. (Some older processors, such as the AMD Athlon XP, have smaller heat spreaders and so require a correspondingly smaller amount of goop.)

If you apply too much thermal goop, the excess squooshes out from between the heatsink base and the CPU surface when you put the heatsink in place. Good practice suggests removing excess goop from around the socket, but that may be impossible with a large heatsink, because the heatsink blocks access to the socket area. Standard silicone thermal goop does not conduct electricity, so there is no danger of excess goop shorting anything out.

If you're a neatnik, use your finger (covered with a latex glove or plastic bag) to spread thin layers of goop on the processor surface and heatsink base before you install the HSF. We do that with silver-based thermal compounds, which we don't trust to be electrically nonconductive, despite manufacturers' claims to the contrary.


The next step is to orient the CPU cooler above the processor, as shown in Figure 5-16, keeping it as close to horizontal as possible. Slide the CPU cooler down into the retaining bracket, making sure that the lock tabs on each of the four corners of the CPU cooler assembly are aligned with the matching slots in the CPU cooler retaining bracket on the motherboard. Press down gently and use a small circular motion to spread the thermal goop evenly over the surface of the processor.







Make sure that both of the white plastic cam levers (one is visible near Barbara's thumb in Figure 5-16) are in the open position, not applying any pressure to the CPU cooler mechanism. With the CPU cooler aligned properly, press down firmly, as shown in Figure 5-17, until all four locking tabs snap into place in the corresponding slots on the retaining bracket. This step requires applying significant pressure evenly to the top of the CPU cooler mechanism. It's generally easier to do that using your full hand rather than just your fingers or thumbs. With some CPU coolers, it may be easier to get two opposite corners snapped in first and then do the remaining corners.






With the CPU cooler snapped into the retaining bracket, the next step is to clamp the heatsink tightly against the processor to ensure good thermal transfer between the CPU and heatsink. To do so, pivot the white plastic cam levers from their unlocked position to the locked position, as shown in Figure 5-18.









EASY DOES IT

The first lever is easy to lock into position, because there is not yet any pressure on the mechanism. With the first lever cammed into its locked position, though, locking the second lever requires significant pressure. So significant, in fact, that the first time we tried to lock the second lever, we actually popped it out of the bracket. If that happens to you, unlock the first camming lever and snap the second one back into position. You may need to squeeze the pivot point with one hand to keep that lever from popping out of place again while you lock the lever with the other hand.



The thermal mass of the heatsink draws heat away from the CPU, but the heat must be dissipated to prevent the CPU from eventually overheating as the heatsink warms up. To dispose of excess heat as it is transferred to the heatsink, most CPU coolers use a muffin fan to draw air continuously through the fins of the heatsink.


YOUR MILEAGE MAY VARY

Different CPU coolers use different retention mechanisms. The CPU coolers bundled with retail-boxed CPUs are designed to be secured using the standard socket or bracket arrangement for the socket type in question. Some third-party CPU coolers use custom mounting arrangements. If you are installing such a CPU cooler, follow the directions included with the CPU cooler.


Some CPU fans attach to a drive power connector, but most (including this Intel unit) attach to a dedicated CPU fan connector on the motherboard. Using a motherboard fan power connector allows the motherboard to control the CPU fan, reducing speed for quieter operation when the processor is running under light load and not generating much heat, and increasing fan speed when the processor is running under heavy load and generating more heat. The motherboard can also monitor fan speed, which allows it to send an alert to the user if the fan fails or begins running sporadically.

To connect the CPU fan, locate the 3-pin header connector on the motherboard labeled "CPU fan," and plug the keyed cable from the CPU fan into that connector, as shown in Figure 5-19.





Installing the new processor (Socket 775)

Intel's current Socket 775 (also called Socket T) processors require slightly different installation steps than processors that use Socket 462 (A), 478, 754, or 939. This section illustrates those differences.

The fundamental difference between Socket 775 and other current processor sockets is that Socket 775 places the pins in the socket and the matching holes on the processor body rather than the converse. That means the pins are vulnerable, so Socket 775 motherboards use a plastic shield to protect the socket until the processor is installed. To begin installing a Socket 775 processor, simply snap out the socket shield, shown in Figure 5-20.








WASTE NOT, WANT NOT

Save the socket shield for future use, or install it on the old motherboard to protect its socket.


With the socket shield removed, the socket itself is visible, as shown in Figure 5-21. The metal bracket that surrounds the socket is the processor retaining bracket, which is locked in place by the hook-shaped lever visible to the left of the socket. Release that lever and swing it vertically to unlatch the processor retaining bracket.







With the lever unlatched, swing the processor retaining bracket upward to make the socket accessible, as shown in Figure 5-22.







Figure 5-23 shows the two keying mechanisms used by Socket 775. A triangle is visible at the lower-right corner of the processor, pointing to the one beveled corner of the socket. Also visible near the lower-left and -right corners of the processor are two keying notches, which mate with two protrusions in the socket body. Make sure that the processor is aligned properly with the socket, and then simply drop it into place.







After you drop the processor into the socket, lower the processor retaining bracket, as shown in Figure 5-24. The retaining bracket is secured by the cammed portion of the latching lever against the lip visible at the bottom of the bracket. Make sure that the latching lever is raised far enough for the cammed portion to clear the lip on the bracket, and use finger pressure to close the retaining bracket until it seats.







With the bracket lip and latching lever aligned, press down firmly on the latching lever until it snaps into place under the latch, as shown in Figure 5-25. Use a paper towel or soft cloth to polish the top of the processor, as described in the previous section.








Magic Marker?

In case you're wondering, the processor shown is a Pentium D 820 engineering sample, hand-labeled by Intel before they sent it to us.


Socket 775 uses a different mechanism to secure the CPU cooler. Rather than using a plastic bracket surrounding the socket, like Socket 478, Socket 775 uses four mounting holes arrayed at the corners of the socket. Figure 5-26 shows a typical Socket 775 CPU cooler, in this case a stock Intel unit. The white square visible at the center of the copper heatsink base is a phase-change thermal pad. If your heatsink has such a pad, you needn't apply thermal compound. If your heatsink lacks a thermal pad, apply thermal compound to the top of the processor before proceeding.







To mount the CPU cooler, align it so that each of its four posts matches one of the motherboard mounting holes. Those holes form a square, so you can align the CPU cooler in any of four positions. Locate the CPU fan power connector on the motherboard and orient the CPU cooler so that the fan power cable is located near the power connector. Make sure the four posts visible at each corner are aligned with the mounting holes, as shown in Figure 5-27, and then seat the CPU cooler.








Strip Before Using

Some thermal pads that are pre-installed on CPU coolers include a paper or thin plastic protective sheet that must be removed before the CPU cooler is installed. Examine the thermal pad carefully and, if necessary, strip off the protective sheet before you install the CPU cooler.


The CPU cooler is now connected to the motherboard but not yet locked into place. Press down on the top of each of the mounting posts, as shown in Figure 5-28, to expand the tips of the mounting posts and secure the CPU cooler in position. (If you need to remove the CPU cooler later, simply lift up each of the four posts to unlock the connectors. The CPU cooler can then be lifted off without resistance.)

Connect the CPU fan cable to the CPU fan connector to complete the processor installation.







CPU Troubleshooting

In one sense, there's not much troubleshooting to be done for a processor. A properly installed processor simply works. If it stops working, it's dead and needs to be replaced. That seldom happens we're tempted to say "never" unless the processor incurs lightning damage, is the victim of a catastrophic motherboard failure, or overheats severely (usually from misguided attempts at overclocking, or running the processor faster than its design speed). A processor in a system with a high-quality motherboard and power supply that is protected by a UPS or a good surge protector is likely to outlast the useful life of the system.


OLD PROCESSORS NEVER DIE

In our more than 20 years' experience with many hundreds of systems, we can count on one finger the number of processors that have failed other than as a result of power spikes, overheating, or other abuse. And we suspect that one was killed by a power glitch.


In recognition of the primary danger, modern processors incorporate thermal protection, which slows down the processor or stops it completely if the temperature rises too high. Even if the processor isn't throttling throughput, operating it at a high temperature can reduce its life. Accordingly, it's important to monitor processor temperature, at least periodically, and if necessary, to take steps to improve processor cooling. If your system slows down for no apparent reason or hangs completely, particularly in a warm environment or when the processor is working hard, it's quite possible that overheating is responsible. Here are the most important steps you can take to avoid overheating:



Keep an eye on processor temperature.

Use the motherboard monitoring program, or reboot the system, run BIOS Setup, and view the temperature and fan speed section. Take these measurements when the system has been idle as well as when it has been running under heavy load. It's important to do this initially to establish a "baseline" temperature for the processor when it is idle and under load. You can't recognize abnormally high temperatures if you don't know what the normal temperature should be. If you run the motherboard monitoring program, set reasonable tripwire values for temperatures and configure the program to notify you when those temperatures are exceeded.


HOW COOL IS COOL ENOUGH?

As our editor pointed out, if you've installed the CPU cooler or thermal compound improperly, the baseline temperature you measure may be much too high and you may not realize that. It's impossible to say what a "normal" temperature is, because so much depends on the particular processor and CPU cooler, the case and cooling fans you use, the ambient room temperature, and so on. As a rule of thumb, with the processor at idle in a standard mini-tower case, we consider a processor temperature under 35 C to be good; the 35 C to 40 C range to be acceptable; and anything over 40 C to be good reason to improve the cooling by using a better CPU cooler and/or better case fans. If you're using a small form factor case or a hot-running processor, such as a Prescott-core Pentium 4, normal idle temperatures may be 5 C to 10 C warmer. Under heavy load, the processor temperature may increase 20 C or more. We consider anything up to 60 C normal. At 65 C we are concerned. At 70 C, we shut the system down and determine what's causing the high temperatures. Some serious gamers routinely run their processors at 80 C or even 85 C, but doing that may shorten processor lifetime dramatically.




Keep the system clean.

Blocked air vents can increase processor temperature by 20 C (36 F) or more. Clean the system as often as is necessary to maintain free air flow. If your case has an inlet air filter, check that filter frequently and clean it as often as necessary.



Use a good CPU cooler.

CPU coolers vary greatly in efficiency (and noise level). Although the CPU cooler bundled with a retail-boxed processor is reasonably efficient, replacing it with a good aftermarket CPU cooler can reduce CPU temperature by 5 to 10 C (9 to 18 F). Make sure that the processor surface is clean before you install the CPU cooler, use the right amount of a good thermal compound, and make sure that the heatsink is clamped tightly against the processor.



Install supplemental case fans.

In particular, if you've upgraded the processor or installed a high-performance video adapter, it's possible that you've added more heat load than the case was designed to handle. Adding a supplemental fan, or replacing an existing fan with one that provides higher air flow, can reduce interior case temperatures dramatically, which in turn reduces processor temperature.


TAKE YOUR SYSTEM'S TEMPERATURE

You can use an ordinary thermometer to test the adequacy of your system fans. Measure the ambient room temperature first. Then put the thermometer close to the outputs of the power supply fan and the supplemental case fan(s). If the temperature difference is 5 C (9 F) or less, adding or upgrading fans probably won't help.




Upgrade the case.

In most systems, the processor is the major heat source. A TAC (Thermally Advantaged Chassis) case provides a duct (and sometimes a dedicated fan) to route waste CPU heat directly to the outside of the case, rather than exhausting it inside the case. In our testing, using a TAC-compliant case routinely lowered CPU temperatures by 5 to 10 C (41 to 50 F) relative to running that CPU in a non-TAC case.

You can buy a TAC case, or, if you're handy with tools, turn your old case into a TAC case. To do so, simply use a 2' to 3' hole saw to cut a hole in the case side panel directly over the CPU. Make a duct of the appropriate length using cardboard or plastic tubing, and secure the duct to the case with screws or adhesive. If you want to be fancy, you can install a standard case fan between the interior panel wall and the duct.



Position the system properly.

As amazing as it sounds, changing the position of the case by only a few inches, and in some pretty non-obvious ways, can make a major difference in system and processor temperature. For example, Robert's main office system sits on the floor next to his desk, directly in front of a heating vent. During the summer, when the air conditioning is running, that processor routinely operates 5 C cooler than during the winter months, when Robert closes the vent to prevent hot air from blowing on the system. That might seem reasonable, until you realize that the cool air from the vent is blowing on the back of the system, which has only exhaust fans. The ambient room temperature is actually lower during winter months and the ambient air is what's being drawn into the system so we'd have expected the system temperature also to be lower in winter.


INCHES MATTER

During the writing of this section, Barbara commented to Robert that his den system was much louder than usual. Sure enough, it was. That system sits between one side of a love seat and the side of a corner table. It had somehow been moved, slid back by only four inches or so, but that was enough to reduce the air flow significantly. The CPU fan was screaming running at about 5,700 RPM and the CPU temperature was 52 C with the system idling. Robert slid the system out a few inches, and within minutes the CPU fan speed had dropped to about 1,800 RPM becoming nearly silent and the idle CPU temperature had fallen to 38 C. Inches can make a huge difference.


Despite the odds, processors do sometimes fail. If you are reasonably certain that your processor has failed, the only practical way to troubleshoot it is to install the problem processor in another system or to install a known-good processor in the problem system. The former is the safer choice. We have never heard of a failed processor harming a good motherboard, but a catastrophically failed motherboard that has killed one processor could easily kill another. For that reason, if we're convinced that a processor is bad, we always pull it and test it in another system.