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PC Hardware in a Nutshell, Second Edition by Barbara Fritchman Thompson, Robert Bruce Thompson

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Choosing a Processor

The processor you choose determines how fast the system runs, and how long it will provide subjectively adequate performance before you need to replace the processor or the system itself. Buying a processor just fast enough to meet current needs means that you’ll have to upgrade in a few months. But processor pricing has a built-in law of diminishing returns. Spending twice as much on a processor doesn’t buy twice the performance. In fact, you’ll be lucky to get 25% more performance for twice the money. So although it’s a mistake to buy too slow a processor, it’s also a mistake to buy one that’s too fast. Consider the following issues when choosing a processor:

Horizon

What kind of applications do you run and how long do you want the system to be usable without requiring an upgrade? If you run mostly standard productivity applications and don’t upgrade them frequently, a low- to low/midrange Celeron or Duron may still be fast enough a year or more after you buy it. If you run cutting-edge games or other demanding applications, buy a midrange or faster processor initially, and expect to replace it every six months to a year. But expect to pay a price for remaining on the bleeding edge.

Hassle

Do you mind upgrading your system frequently? If you don’t mind replacing the processor every year, you can get most of the performance of a high-end system at minimal cost by replacing the processor every year or so with the then-current midrange processor.

Trade-offs

If you’re working on a fixed budget, don’t spend too much on the processor to the detriment of the rest of the system. You may be better off, for example, settling for a midrange Celeron and spending the extra money on more memory, a faster hard disk, or a bigger monitor. A Celeron/1200 with 256 MB RAM blows the doors off a Pentium 4/2.0G with 32 MB RAM every day of the week. Don’t make yourself “processor poor.”

Form factor

Keep form factor in mind when you’re shopping for a processor, particularly if you’re also buying a motherboard.

Socket 7

Don’t consider buying a Socket 7 processor, except as an inexpensive (<$30) upgrade for an existing PC. Spending much more than that on Socket 7 is wasting money. Retire the old system to less demanding duties, and build or buy a new system instead.

Slot 1

During 2001, Slot 1 slid from obsolescent to obsolete. Although Slot 1 motherboards and processors are likely to remain in limited distribution well into 2002 and perhaps beyond, do not choose Slot 1 for a new system. An existing Slot 1 system may or may not be a good upgrade candidate depending on the motherboard characteristics. Some Slot 1 motherboards support fast Pentium III processors, and can be upgraded at reasonable expense. Other Slot 1 motherboards have neither BIOS support nor adequate VRMs to support faster processors. Although it’s possible to upgrade those systems with marginally faster Slot 1 processors, doing so makes no economic sense. Before you upgrade any Slot 1 system, check prices carefully. The higher price of Slot 1 processors means you may be able to replace the motherboard and processor with Socket 370 Celeron/Pentium III components or Socket 478 Pentium 4 components for little more than the cost of the Slot 1 processor alone.

Slot A

Like Intel processors, AMD Athlon processors were originally produced in slotted versions, which were subsequently replaced by socketed versions. Slot A motherboards and processors remain in limited distribution, and will likely remain so throughout 2002, but do not choose Slot A parts for a new system. Upgradability of an existing Slot A system is determined by its chipset. Motherboards based on the AMD 750 chipset can use Slot A processors based on the K7, K75, and Thunderbird cores (although Slot A Thunderbirds are difficult to find). Motherboards based on the VIA KX133 chipset are incompatible with Slot A Thunderbird Athlon processors, but can use Athlons based on the K7 and K75 cores.

Socket 370

As of June 2002, Socket 370 is a dying standard because Intel is pulling out all the stops to push their Pentium 4 at the expense of their sixth-generation Celeron and Pentium III processors. Socket 370 motherboards and processors are likely to remain in good supply throughout 2002. We think a fast Socket 370 processor still makes sense for building inexpensive systems, as long as you’re aware that upgrade options after 2002 are likely to be minimal. If you are building a new Socket 370 system, make sure to buy a “Universal” Socket 370 motherboard, which is to say one that supports all Socket 370 processors including the Tualatin-core Celeron and Pentium III. Those processors are likely to remain available in faster versions for some time to come. If you are upgrading an older Socket 370 system, be very careful to verify compatibility between your motherboard and the new Socket 370 processor you propose to buy. There are many incompatibilities between older motherboards and newer processors. Some can be solved with a simple BIOS update, but many are unfixable because the older motherboard’s chipset or VRMs do not support newer Socket 370 processors.

Socket A

AMD has done a much better job than Intel at maintaining backward compatibility between older Socket A motherboards and newer Socket A processors. Socket A processors are a good choice for a new system (assuming you also buy a stable, high-quality Socket A motherboard, which is easier said than done) and are likely to remain so throughout 2002 and well into 2003. If your goal is to build a dual-processor system, your best option is a pair of Socket A Athlon MP processors running in an AMD 760MPX-based motherboard. As always, an older motherboard may have BIOS or VRM issues with newer processors, so you still need to verify compatibility. But in general, older model Socket A motherboards can use newer model Socket A processors, although perhaps not the fastest models.

Socket 423

Socket 423 was Intel’s first socket for the Pentium 4, and was simply a stopgap solution that allowed Intel to bring Pentium 4 processors to market quickly to compete with the AMD Athlon on clock speed. Socket 423 processors and motherboards are obsolete, although they are likely to remain in limited distribution throughout 2002. Socket 423 is a very poor choice for a new system, as Intel is very unlikely ever to produce Pentium 4 processors faster than 2.0 GHz for Socket 423. An existing Socket 423 system is a poor upgrade candidate because of the lack of faster processors. It is possible to upgrade an older Socket 423 system, but the fastest available Socket 423 processor will be only marginally faster than the processor already installed.

Socket 478

Socket 478 is Intel’s “real” Pentium 4 solution, and is likely to remain in production through at least late 2003. A Socket 478 processor is the best choice if you are building a new mainstream system. An existing Socket 478 system can easily be upgraded simply by dropping in a faster Socket 478 processor, a condition that is likely to remain true for some time. As always, it’s possible that BIOS, chipset, and VRM issues may restrict the speed of the fastest Socket 478 processor that can be installed in a particular motherboard, but Socket 478 currently offers the best options for future upgradability.

When upgrading a system, the existing motherboard determines upgradability, as follows:

486 motherboards

It is not cost effective to upgrade 486 systems. Evergreen, Kingston, and others sell CPU upgrade kits that increase performance significantly, but these kits are based on low-end processors and are quite expensive. For the same cost, you can buy a new motherboard, processor, and RAM to replace what you already have. Upgrading the processor in a 486 is a sucker bet.

Socket 4, Socket 5, and older Socket 7 motherboards

The original P54 60 and 66 MHz Pentiums fit Socket 4 motherboards. Socket 5 systems use Pentium P54C processors. Older Socket 7 systems use Pentium P55C processors. Again, although upgrade processors remain available for these systems, buying one is not a cost-effective upgrade. Replace the motherboard and install a modern processor.

Super Socket 7 motherboards

If your system has a Super Socket 7 motherboard, a few upgrade alternatives exist. Although supplies are limited and they can be hard to find, you can install an AMD K6-2 or a VIA Cyrix MII. Either offers much higher performance than older Pentium-class processors, albeit much lower performance than even entry-level current processors. Still, for $30 or so, you may be able to extend the useful life of an older system by installing one of these processors. Before you attempt the upgrade, check the web sites for the processor and motherboard, and expect to have to do a BIOS upgrade.

Slot 1 motherboards

Intel no longer produces Slot 1 Pentium II and Celeron processors, although they remain in limited distribution. Fortunately, some Slot 1 motherboards can be upgraded by using a slocket adapter, which accepts a Socket 370 processor and plugs into the motherboard Slot 1. The best candidates for such upgrades are motherboards designed for the Pentium III that support the 100 MHz or 133 MHz FSB. Even if a particular motherboard can be upgraded via slocket, it may be limited by BIOS, chipset, or VRM issues as to which particular Socket 370 processors are usable. In general, FC-PGA Celerons are the most likely to work, assuming that the motherboard supports the Celeron L2 caching method. An FC-PGA Coppermine-core Pentium III may or may not work, depending on the particular slocket/processor combination, and the chipset and BIOS configuration of the motherboard. We know of no slocket that allows FC-PGA2 Celerons and Pentium IIIs be used in Slot 1 motherboards. Before you attempt to upgrade a Slot 1 motherboard with a slocket, verify with the slocket maker that the slocket, processor, and motherboard you plan to use are compatible.

Slot A motherboards

Slot A processors remain in limited distribution, although availability of those processors is rapidly waning as time passes. AMD 750-based Slot A motherboards can accept any type of Slot A processor, including those that use the K7, K75, or Thunderbird core, although BIOS and VRM limitations may restrict the fastest speed you can use. VIA KX133-based motherboards can be upgraded with a K7- or K75-based Slot A processor, but not a Slot A Thunderbird processor. In general, though, we recommend upgrading Athlon systems to Socket A rather than spending good money on obsolete Slot A parts. The low prices of Socket A processors and motherboards, as well as the low price of memory, mean that you can install a new motherboard, processor, and DDR-SDRAM memory for only a hundred dollars or so more than the cost of a new Slot A processor.

Socket 370 motherboards

Upgrading a Socket 370 system should be easy. Unfortunately, it often isn’t. The problem with upgrading Socket 370 motherboards is that there have been so many variants of the socket itself and the processors intended to fit it that determining compatibility can be difficult. Any Socket 370 processor physically fits any Socket 370 socket, but there are actual pinout differences between early Socket 370 sockets and processors and later versions. Late-model Socket 370 processors—Coppermine- and Tualatin-core Celerons and Pentium IIIs—will not operate in early-model Socket 370 motherboards, and early-model Socket 370 processors—Mendocino-core Celerons and Katmai-core Pentium IIIs—may or may not operate in later-model Socket 370 motherboards. In addition, chipset issues are important with Socket 370, because early Socket 370 chipset revisions do not support later Socket 370 processors, even though the processor is otherwise compatible electrically and physically with the socket. Intel rationalized this situation in late 2001 by introducing their so-called “Universal” Socket 370 motherboards, which can accept any Socket 370 processor. If you intend to upgrade the processor in a Socket 370 system, the best advice is first to determine exactly what motherboard you have (including revision level). Once you’ve done that, visit the motherboard maker’s web site and read the technical documentation to determine which currently available Socket 370 processors can be used in that motherboard.

Socket A, Socket 423, and Socket 478

Motherboards that use any of these sockets can be upgraded using current processors. As always, check the documentation for the motherboard to ensure that it supports the type, FSB speed, and clock speed of the processor you plan to install. Ordinarily, such upgrades are relatively straightforward, requiring a BIOS upgrade at most.

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