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

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Advanced Micro Devices (AMD) Processors

Until late 1999, Intel had the desktop processor market largely to itself. There were competing incompatible systems such as the Apple Mac, based on processors from Motorola, IBM, and others, but those systems sold in relatively small numbers. Some companies, including Cyrix, IDT, Harris, and AMD itself, made Intel-compatible processors, but those were invariably a step behind Intel’s flagship processors. When those companies—which Intel calls “imitators”—were producing enhanced 286s, Intel was already shipping the 386 in volume. When the imitators began producing enhanced 386-compatible processors, Intel had already begun shipping the 486, and so on. Each time Cyrix, AMD, and the others got a step up, Intel would turn around and release the next-generation processor. As a result, these other companies’ processors sold at low prices and were used largely in low-end systems. No one could compete with Intel in their core market.

All of that changed dramatically in late 1999, when AMD began shipping a processor called the Athlon. The Athlon didn’t just match the best Intel processors. It was faster than the best Intel could produce, and was in many respects a more sophisticated processor. Intel had a fight on its hands, and it’s remained so to the present day.

If you ever take a moment to appreciate how much processor you can get for so little money nowadays, give thanks to AMD. Without AMD, we’d all still be running sixth-generation Intel processors at 500 MHz or so. An entry-level Intel processor would cost $200 or $250, and a high-end one (that might run at 750 MHz) would probably cost $1,000 or more. The presence of AMD as a worthy competitor meant that Intel could no longer play the game of releasing faster processors in dribs and drabs at very high prices. Instead, they had to fight for their lives by shipping faster and faster processors at lower and lower prices. We all have AMD to thank for that, and Intel should thank AMD as well. Although we’re sure Intel wishes AMD would just disappear (and vice versa), the fact is that the competition has made both Intel and AMD better companies, as well as providing the obvious benefits to us, the users.

The following sections describe current and recent AMD processor models.

The AMD Athlon Family

The AMD Athlon, which was originally codenamed the K7 and began shipping in August 1999, was the first Intel-compatible processor from any maker that could compete on equal footing with mainstream Intel processors of the time. First-generation Athlon processors matched or exceeded Katmai-core Pentium III processors in most respects, including (for the first time ever) floating-point performance. Intel finally had a real fight on its hands.

Although AMD represented the Athlon as the first seventh-generation processor, we regard the K7 Athlon as essentially an enhanced sixth-generation processor. Athlon has, in theory, several advantages relative to the aging Intel sixth-generation architecture, including the ability to perform 9 operations per clock cycle (versus 5 for the Pentium III); more integer pipelines (3 versus 2); more floating-point pipelines (3 versus 1); a much larger L1 cache (128 KB versus 32 KB); more full x86 decoders (3 versus 1); and a faster FSB (100 MHz double-pumped to 200 MHz by transferring data on both the rising and falling edges of the clock cycle versus the single-pumped Intel 100/133 MHz bus, which transfers data only once during a clock cycle). While all that was very nice, tests showed that in practice the K7 Athlon and Pentium III were evenly matched at lower clock speeds, with the Pentium III sometimes showing a slight advantage in integer performance, and the Athlon a slight advantage in floating-point performance. At higher clock speeds, however, where the Pentium III L2 cache running at full CPU speed comes into play, the Coppermine Pentium III won most benchmarks handily.

AMD produced two variants of the first-generation Athlon, both in Slot A form. The earliest Athlons used the 0.25μ K7 core, but AMD transitioned within a few months to the improved 0.18μ K75 core, which was codenamed Pluto for speeds lower than 1 GHz and Orion in the 1 GHz model. Although the K7 and K75 Athlons are good processors, they have the following drawbacks:

Poor chipset and motherboard support

Initial acceptance of the Athlon was hampered because the only chipset available was the AMD-750, which was originally intended as a technology demonstrator rather than as a production chipset. The VIA KX133 chipset, originally planned to ship at the same time as the Athlon, was significantly delayed, and motherboards based on the KX133 began shipping in volume only in Q2/2000. Many motherboard manufacturers delayed introducing Athlon motherboards, and their first products were crude compared to the elegant motherboards available for the Pentium III. In addition to indifferent quality, stability, compatibility, performance, and features, first-generation Athlon motherboards were in short supply and relatively expensive compared to comparable models for the Pentium III. In addition, KX133-based motherboards have problems of their own, including their inability to support Slot A Thunderbird-core Athlons. AMD soon made it clear that Slot A was an interim solution and that they would quickly transition to Socket A, so manufacturers devoted little effort to improving orphaned Slot A motherboards.

Fractional CPU-speed L2 cache

Like the Deschutes-core Pentium II and the Katmai-core Pentium III, K7 Athlons used L2 cache running at half CPU speed. Unlike the Coppermine Pentium III, which uses on-die L2 cache running at full CPU speed, the Athlon uses discrete L2 cache chips, which AMD must buy from third parties. The Athlon architecture allows running L2 cache at anything from a small fraction of CPU speed to full CPU speed. AMD has taken advantage of this as they have introduced faster versions of the Athlon by reducing the speed of L2 cache relative to processor speed, allowing them to use less expensive L2 cache chips. The Athlon/700 and slower run L2 cache at 1/2 CPU speed; the Athlon/750, /800, and /850 run L2 cache at 2/5 CPU speed. The Athlon/900 and faster run L2 cache at 1/3 CPU speed. Unfortunately, compared to the full-speed Pentium III Coppermine L2 cache, the slow L2 cache used on fast Athlons decreases performance substantially in many applications.

High power consumption

Athlon processors are power-hungry, with some 0.25μ models consuming nearly 60 watts. In comparison, typical Intel processors use one-half to one-third that amount. High power consumption and the resulting heat production has many implications, including the requirement for improved system cooling and larger power supplies. In fact, for the Athlon, AMD took the unprecedented step of certifying power supplies for use with their processor. If you build a system around a first-generation Athlon, you must make sure that both cooling and power supply are adequate to meet the extraordinarily high current draw and heat dissipation of the processor.

Lack of SMP support

Until mid-2001, no multiprocessor Athlon systems existed. Although all Athlon processors from the earliest models have been SMP-capable (and in fact use the superior point-to-point SMP method rather than Intel’s shared bus method), dual-processor Athlon systems had to wait for the release of the AMD 760MP chipset (originally designated the AMD 770) in mid-2001. This early absence of SMP support hurt Athlon acceptance in the critical corporate markets, not so much because there was a huge demand for SMP but because the lack of SMP support led buyers to consider the Athlon a less advanced processor than Intel’s offerings.

With the exception of SMP support, which was never lacking in the processor, these faults were corrected in the second generation of Athlon CPUs, which are based on the enhanced K75 core codenamed Thunderbird. All early Athlon models used Slot A, which is physically identical to Intel’s SC242 (Slot 1), but uses EV-6 electrical signaling rather than the GTL signaling used by Intel. Figure 4-10 shows a Slot A Athlon processor.

A Slot A Athlon processor (image courtesy of Advanced Micro Devices, Inc.)

Figure 4-10. A Slot A Athlon processor (image courtesy of Advanced Micro Devices, Inc.)

Table 4-3 lists the important characteristics of Slot A Athlon variants. Thunderbird processors were produced in very small numbers in Slot A for OEM use and so are included in this table for completeness, but we’ve never actually seen a Slot A Thunderbird and don’t know anyone who has.

Table 4-3. Slot A Athlon variants

Processor

Athlon

Athlon

Athlon

Athlon

Athlon

Athlon

Core

K7

K75

K75

K75

Thunderbird

Thunderbird

Model

1

2

2

2

4

4

Production dates

1999, 2000

2000

2000

2000

2000, 2001

2000, 2001

Clock speeds (MHz)

500, 550, 600, 650, 700

550, 600, 650, 700

750, 800, 850

900, 950, 1000

750, 800, 850

900, 950, 1000

L2 cache size

512 KB

512 KB

512 KB

512 KB

256 KB

256 KB

L2 cache speed

1/2 CPU

1/2 CPU

2/5 CPU

1/3 CPU

CPU

CPU

L2 cache bus width

64 bits

64 bits

64 bits

64 bits

64 bits

64 bits

System bus speed

100 MHz

100 MHz

100 MHz

100 MHz

100 MHz

100 MHz

Core voltage

1.6

1.6

1.6 (750) 1.7 (800/850)

1.8

1.7

1.75

I/O voltage

3.3

3.3

3.3

3.3

1.7

1.75

Dual CPU capable

Slot A Athlon variants

Slot A Athlon variants

Slot A Athlon variants

Slot A Athlon variants

Slot A Athlon variants

Slot A Athlon variants

Fabrication process

0.25 μ

0.18 μ

0.18 μ

0.18 μ

0.18 μ

0.18 μ

Interconnects

Al

Al

Al

Al

Al/Cu

Al/Cu

Die size (mm2)

184

102

102

102

120

120

Transistors (million)

22

22

22

22

37

37

Like Intel, with its shift from Slot 1 to Socket 370 for low-end processors, AMD recognized that producing cartridge-based slotted processors was needlessly expensive for the low end, and made it more difficult to compete in the value segment. Also, improvements in fabrication made it possible to embed L2 cache directly on the processor die rather than using discrete cache chips. Accordingly, AMD developed a socket technology, analogous to Socket 370, which they called Socket A. AMD had never denied that Slot A was a stopgap technology, and that Socket A was their mainstream technology of the future. AMD rapidly phased out Slot A during 2000, and by late 2000 had fully transitioned to Socket A. AMD has to date produced five major desktop processor variants in Socket A. From earliest to latest, these include:

Athlon (Thunderbird-core)

The Thunderbird Athlon was originally designated Athlon Professional and targeted at the mainstream desktop and entry-level workstation market, in direct competition with the Intel Pentium III and Pentium 4. The first Thunderbird processors used an 0.18μ process with aluminum interconnects, but by late 2000 AMD had transitioned to a 0.18μ process with copper interconnects. During that transition, AMD phased out Slot A Thunderbird models, and shifted entirely to Socket A. Early Thunderbirds used the 100 MHz FSB (double-pumped to 200 MHz), with later models also available in 133 MHz FSB variants. Figure 4-11 shows a Socket A Athlon Thunderbird processor.

A Socket A Athlon Thunderbird processor (image courtesy of Advanced Micro Devices, Inc.)

Figure 4-11. A Socket A Athlon Thunderbird processor (image courtesy of Advanced Micro Devices, Inc.)

Duron (Spitfire-core)

The Duron, codenamed Spitfire and for a short time designated Athlon Value, was targeted at the value desktop market and was to be a Celeron-killer. With it AMD straddled a fine line between matching Celeron clock speeds and performance on the one hand, versus avoiding cannibalizing sales of Athlon processors on the other. Accordingly, AMD differentiated the Duron by limiting the clock speed of the fastest current Duron to one step below the clock speed of the slowest current Athlon, by using a smaller and less efficient L2 cache, and by making the Duron only in 100 MHz FSB versions (versus the 133 MHz FSB available on some Athlon models). The Duron is a superb processor, and unquestionably offers more bang for the buck than any other processor sold by AMD or Intel. Although it achieved reasonable sales volumes in Europe it never really took off in the U.S. because of the absence of high-quality integrated Duron motherboards.

Tip

There was to have been another variant of the Thunderbird-core Athlon, codenamed Mustang and formally named Athlon Ultra, but that processor never shipped except as samples. Mustang was to be a Socket A part, targeted at servers and high-performance workstations and desktops. It was to be an enhanced version of Thunderbird, with reduced core size, lower power consumption, and large, full-speed, on-die L2 cache, probably 2 MB or more. Mustang was to have used a 133 MHz DDR FSB, yielding an effective FSB of 266 MHz. It was intended to use a 0.18μ process with copper interconnects from the start, and to require the AMD 760 chipset or later. Alas, the Mustang never shipped. It would have been a wonderful processor.

Athlon XP (Palomino-core)

AMD originally intended to name the Palomino-core Athlon the Athlon 4, for obvious reasons. In fact, the first Palomino-core Athlons that shipped were the Mobile Athlon 4 and the 1.0 GHz and 1.2 GHz versions of the Athlon MP. Instead, given Microsoft’s schedule for introducing Windows XP, AMD decided their new processor might tag along on the coattails of the new Windows version. Accordingly, AMD finally named the Palomino-core Athlon the Athlon XP. Various architectural changes from the Thunderbird core, detailed below, allow the Athlon XP to achieve considerably higher performance at a given clock speed than a comparable Thunderbird. The Athlon XP is also the first recent AMD processor to use a model designation unrelated to its actual clock speed. Figure 4-12 shows an AMD Athlon XP processor.

AMD Athlon XP processor (image courtesy of Advanced Micro Devices, Inc.)

Figure 4-12. AMD Athlon XP processor (image courtesy of Advanced Micro Devices, Inc.)

Athlon MP (Palomino-core)

Even the first Athlon processors had the circuitry needed to support dual-processor operation, but that remained a non-issue until the introduction of the AMD 760MP chipset because no prior Athlon chipset supported dual processors. In mid-2001, Tyan began shipping their 760MP-based Thunder motherboard, which supported dual Athlons, but it was quite expensive and required a special power supply. In late 2001, Tyan began shipping the inexpensive Tiger MP dual Athlon board, which used a standard power supply. Suddenly dual Athlon systems were possible, and many enthusiasts set out to build one. AMD capitalized on this new market by introducing Palomino-core Athlon XP processors certified for dual-processor operation, which they named the Athlon MP. In truth, a pair of standard Athlon XPs or even Durons work properly in the Tyan MP boards. Many hobbyists have successfully used them so, but the Athlon MP provides a higher comfort level for OEMs and corporations who produce and buy dual Athlon systems.

Duron (Morgan-core)

The Morgan-core Duron is simply a refresh of the Spitfire Duron to use the newer Palomino core. The advantages of the Morgan-core Duron over the Spitfire-core Duron are analogous to the advantages of the Palomino-core Athlon over the Thunderbird-core Athlon. The Morgan core is essentially a Palomino core with a smaller and less efficient L2 cache. As with the Spitfire, AMD carefully manages the Morgan to prevent cannibalizing sales of the Athlon XP. The fastest current Morgan is always at least one step slower than the slowest current Athlon XP. In terms of absolute performance clock-for-clock, the Morgan slightly outperforms the Coppermine-core Pentium III and the Tualatin-core Celeron. If you’re looking for the absolute highest bang for your processor buck, a Morgan-core Duron is the processor to choose. Figure 4-13 shows an AMD Duron processor.

AMD Duron processor (image courtesy of Advanced Micro Devices, Inc.)

Figure 4-13. AMD Duron processor (image courtesy of Advanced Micro Devices, Inc.)

Table 4-4 lists the important characteristics of Socket A Athlon and Duron variants. Note that some examples of the Thunderbird Athlon/750, 800, and 850 use 1.70V rather than 1.75V, and that some examples of the Duron/600, 650, and 700 use 1.5V rather than 1.6V.

Table 4-4. Socket A Athlon and Duron variants

Processor

Athlon

Athlon

Athlon XP

Athlon MP

Duron

Duron

Core

Thunderbird

Thunderbird

Palomino

Palomino

Spitfire

Morgan

Model

4

4

6

6

3

7

Production dates

2000, 2001

2000, 2001

2001 -

2001 -

2000, 2001

2001 -

Clock speeds (MHz)

750, 800, 850, 900, 950, 1000, 1100, 1200, 1300, 1400

1000, 1133, 1200, 1333, 1400

1333, 1400, 1466, 1533, 1600

1000, 1200, 1333, 1400, 1533

600, 650, 700, 750, 800, 850, 900, 950

1000, 1100, 1200

L2 cache size

256 KB

256 KB

256 KB

256 KB

64 KB

64 KB

L2 cache speed

CPU

CPU

CPU

CPU

CPU

CPU

L2 cache bus width

64 bits

64 bits

64 bits

64 bits

64 bits

64 bits

System bus speed

100 MHz

133 MHz

133 MHz

133 MHz

100 MHz

100 MHz

Core voltage

1.75

1.75

1.75

1.75

1.6

1.6

I/O voltage

1.75

1.75

1.75

1.75

1.6

1.6

Dual CPU capable

Socket A Athlon and Duron variants

Socket A Athlon and Duron variants

Socket A Athlon and Duron variants

Socket A Athlon and Duron variants

Socket A Athlon and Duron variants

Socket A Athlon and Duron variants

Fabrication process

0.18 μ

0.18 μ

0.18 μ

0.18 μ

0.18 μ

0.18 μ

Interconnects

Al/Cu

Al/Cu

Cu

Cu

Cu

Cu

Die size (mm2)

120

120

128

128

100

106

Transistors (million)

37

37

37.5

37.5

25

25.18

AMD actually first shipped Palomino-core Athlon processors some months before the Athlon/XP desktop processor in the Athlon 4 mobile variant and the Athlon MP/1.0G and Athlon MP/1.2G variants, all of which were designated by their actual clock speeds. Subsequent Palomino-core Athlon processors are all designated using the QuantiSpeed performance rating rather than their actual clock speeds. For example, the Athlon XP/1500+, XP/1600+, XP/1700+, XP/1800+, and XP/1900+ actually run at clock speeds of 1333, 1400, 1466, 1533, and 1600 MHz, respectively, as do the similarly badged Athlon MP SMP-capable variants.

Although Palomino-core processors use the same 0.18μ fabrication process used for Thunderbird-core processors, AMD made several improvements in layout and architecture. Relative to the Thunderbird-core Athlon, Palomino-core Athlons (including the Athlon XP, the Athlon MP, and the Mobile Athlon 4) provide 3% to 7% faster performance clock-for-clock, and include the following enhancements:

Improved data prefetch mechanism

This allows the CPU, without being instructed to do so, to use otherwise unused FSB bandwidth to prefetch data that it thinks may be needed soon. This single feature accounts for most of the performance improvement in the Palomino core relative to the Thunderbird, and also increases the processor’s dependence on a high-speed FSB/memory bus. Better data prefetch most benefits applications that require high memory bandwidth and have predictable memory access patterns, including video editing, 3D rendering, and database serving.

Enhanced Translation Look-aside Buffers

Translation Look-aside Buffers (TLBs) cache translated memory addresses. Translation is needed for the CPU to access data in main memory. Caching translated addresses makes finding data in main memory much faster. Palomino-core Athlons include the following three enhancements to the TLBs:

More L1 Data TLBs

Palomino-core Athlons increase the number of L1 Data TLBs from 32 to 40. The larger number of TLB entries increases the probability that the needed translated address will be cached, thereby improving performance. Even with 40 entries, though, the Palomino-core Athlon has fewer L1 TLB entries than the Intel Pentium III or Pentium 4, and the benefit of this small increase is minor.

L2 TLBs use exclusive architecture

In Thunderbird-core Athlons, the L1 and L2 TLBs are non-exclusive, which means that data cached in the L1 TLB is also cached in the L2 TLB. With the Palomino core, AMD uses an exclusive TLB architecture, which means that data cached in the L1 TLB is not replicated in the L2 TLB. The benefit of exclusive caching is that more entries can be cached in the L2 TLB. The drawback is that using exclusive caching results in additional latency when a necessary address is not cached in the L2 TLB. Overall, exclusive TLB caching again results in a minor performance increase.

TLB entries can be speculatively reloaded

Speculative reloading means that if an address is not present in the TLB, the processor can load the address into the TLB before the instruction that requested the address has finished executing, thereby making the cached address available without the latency incurred by earlier Athlon cores, which could load the TLB entry only after the requesting instruction had executed. Once again, speculative reloading provides a minor performance improvement.

SSE instruction set support

Palomino-core Athlons support the full Intel SSE instruction set, which AMD designates 3DNow! Professional. Earlier Athlon processors supported only a subset of SSE and so could not set the processor flag to indicate full support. That meant that SSE-capable software could not use SSE on AMD processors, which in turn meant that AMD processors ran SSE-capable software much more slowly than did Intel SSE-capable processors. Palomino-core Athlons set the SSE flag to true, which allows software to use the full SSE instruction set (but not the SSE2 instruction set supported by Intel Pentium 4 processors). Also note that although Palomino-core Athlons support the full SSE instruction set, all that means is that they can run SSE-enabled software. It does not necessarily mean that they run SSE-enabled software as fast as a Pentium III or Pentium 4 processor does.

Reduced power consumption

Palomino-core Athlons have an improved design that reduces power consumption by 20% relative to Thunderbird, which reduces heat production and allows the Palomino core to achieve higher clock speeds than the Thunderbird core.

Tip

Rather oddly, Morgan-core Durons (based on the Athlon Palomino core) actually draw more current than the older Spitfire-core Durons (based on the Athlon Thunderbird core). In fact, Morgan-core Durons draw the same current as Palomino-core Athlons operating at the same clock speed, which leads us to believe that Morgan-core Durons are literally simply Palomino-core Athlons with part of the L2 cache disabled.

Thermal diode

Palomino-core Athlons are the first AMD processors that include a thermal diode, which is designed to prevent damage to the processor from overheating by shutting down power to the processor if it exceeds the allowable design temperature. Intel processors have included a thermal diode for years. It is nearly impossible to damage an Intel Pentium III or Pentium 4 processor by overheating, even by so extreme a step as removing the heatsink/fan from the processor while it is running. Pentium III systems crash when they overheat badly, but the processor itself is protected from damage. Pentium 4 systems don’t even crash, but simply keep running, albeit at a snail’s pace. The AMD thermal diode, alas, is an inferior implementation. Although the thermal diode on an AMD processor can shut down the CPU safely when heat builds gradually (as with a failed CPU fan), it does not react quickly enough to protect the processor against a catastrophic overheating event, such as the heatsink falling off.

Warning

The Godzilla-size heatsink/fan units used on modern high-speed processors cause catastrophic heatsink/fan unit failures more often than you might think. Whereas Pentium 4 processors use a heatsink/fan retention mechanism that clamps securely to the motherboard, AMD processors still depend on heatsink/fan units that clamp to the CPU socket itself, which isn’t designed to support that much weight, particularly in a vertical configuration such as a mini-tower system. If the heatsink/fan unit comes loose, as it may do when the system is shipped or moved, an AMD processor will literally burn itself to a crisp within a fraction of a second of power being applied. We’re talking smoke and flames here. This problem is one of the major causes of AMD systems arriving DOA, but may also occur any time you move an AMD system. So, if you move an AMD system or if you’ve just received a new AMD system, always take the cover off and make sure the heatsink/fan unit is still firmly attached before you apply power to the system. You have been warned.

Although the Athlon XP included some significant technical enhancements over the Thunderbird-core Athlon, the change that received the most attention was AMD’s decision to abandon clock speed labeling and instead designate Athlon XP models with a Performance Rating (PR) system.

AMD K7-, K75-, and Thunderbird-core Athlon processors were labeled with their actual clock speeds. AMD Athlon XP (Palomino-core) processors use AMD’s QuantiSpeed designations, which are simply a revival of the hoary Performance Rating system. Although AMD claims that these PR numbers refer to relative performance of Palomino-core processors versus Thunderbird-core processors, most observers believe that AMD hopes consumers will associate Athlon XP model numbers with Pentium 4 clock speeds. For example, although the AMD Athlon XP/1500+ processor actually runs at 1333 MHz, we think AMD believes buyers will at least subconsciously associate the 1500+ model number with the Pentium 4/1.5G, which does in fact run at a 1,500 MHz clock speed.

AMD has gone to great pains to conceal the actual clock speed of Athlon MP processors from users. For example, they mandate that the actual clock speed not appear in advertisements, and have actually gone so far as to insist that system and motherboard makers modify the BIOS to ensure that it reports only the model number and not the actual clock speed. It’s interesting that AMD trumpeted their faster clock speeds until Intel overtook AMD and left them in the dust in terms of clock speeds. Now that AMD can no longer match Intel’s clock speeds, clock speeds are no longer important. Or so says AMD.

Other AMD Processors

In addition to the flagship Athlon and Duron series, the following AMD processors remain available, albeit in limited distribution:

K6-2

The K6-2 was introduced in mid-1998 as AMD’s alternative to the Intel Pentium II and Celeron. K6-2 integer performance is close to that of a Pentium II or Celeron at the same clock speed, but floating-point performance is noticeably inferior. The K6-2 never sold in large numbers, both because its performance was inferior to Intel alternatives and because the K6-2 ran only in obsolescent Socket 7 motherboards. With the shipment of the Athlon and later the Duron, AMD de-emphasized the K6-2, allowing it to die a slow death. Until early 2001, the K6-2 was still used in a few entry-level PCs. As of June 2002, the K6-2 remains in limited distribution in 500, 533, and 550 MHz versions.

K6-III

The Socket 7 K6-III shipped in Q1/99 at 450 MHz, but the expected faster versions never materialized. Although the K6-III was officially discontinued in spring 2000, some vendors still had limited numbers of the K6-III/400 and /450 in stock as of June 2002, and we expect that these processors will remain available in diminishing numbers throughout 2002. The K6-III was designed to function in any K6-2 motherboard with only a BIOS update. It added a 256 KB on-chip L2 cache, which addressed the long-standing problem of Socket 7 L2 cache being accessible only via the relatively slow memory bus. The K6-III also supports an L3 cache residing on the motherboard, which increases performance, but may introduce subtle problems with existing chipsets. K6-III integer performance generally matches the Celeron at the same clock speed. Floating-point performance is improved relative to the K6-2, but still inferior to Intel.

The introduction of Socket A Athlon and Duron processors sounded the death knell for the AMD K6-* line of processors. Still, as long as they remain available, the K6-2 and K6-III processors are reasonable choices for upgrading a late-model Super Socket 7 system, to the extent that it makes sense to upgrade such a system at all. Before you consider upgrading a system with a K6-series processor, check both the AMD web site (http://www.amd.com) and the motherboard manufacturer’s web site to determine compatibility between the processor and motherboard. In particular, determine whether the motherboard supplies the proper voltages for the processor and whether it requires a BIOS update to support the processor properly.

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