AMD K5 Review

by Anand Lal Shimpi on June 9, 1997 4:43 PM EST
Although near its extinction, the AMD K5 has still got the power to take on your basic business applications and the occasional game. Maxing out at an extremely low 116MHz, the K5's excellent architectural design and amazing core gave it performance which took a 200MHz Pentium to top. The K5, like the Cyrix 6x86, uses the sometimes confusing PR rating system in order to help convince customers to purchase the K5 over "equivalent speed" but more expensive Intel chips.

First Generation AMD SSA/5 Series Microprocessor
Chip Name P-Rating Clock Speed Bus Speed x Multiplier
AMD SSA/5-PR75 PR75 75MHz 50 MHz x 1.5
AMD SSA/5-PR90 PR90 90MHz 60 MHz x 1.5
AMD SSA/5-PR100 PR100 100MHz 66 MHz x 1.5

When the K5 was originally released, it was known as the AMD SSA/5 processor, and came in three varieties, a PR75, PR90, and a PR100 all running at their rated clock speeds (i.e. the PR75 ran at 75MHz and the PR90 ran at 90MHz etc...). Unfortunately, these chips suffered from a poor design and an even worse FPU. Synthetic benchmarks showed the SSA/5 FPU to be lower than the Cyrix 6x86's unit, most real world tests confirmed this. This can be attributed to AMD's problems with getting the K5 out and on the roll, the chip had already experienced many delays and the market demanded something...AMD's answer? A slow performing, yet working prelude to the "actual" K5, or at least the excellent performing processor that AMD had promised all of us. Right after the release of the SSA/5 the K5 went back to the drawing board, this time the core was tweaked, the cache subsystem enhanced, and the FPU given a boost. The result? A new K5-PR100, K5-PR120, and K5-PR133.

First Generation AMD K5 Series Microprocessor
Chip Name P-Rating Clock Speed Bus Speed x Multiplier
AMD K5-PR100 PR100 75MHz 50 MHz x 1.5
AMD K5-PR120 PR120 90MHz 60 MHz x 1.5
AMD K5-PR133 PR133 100MHz 66 MHz x 1.5

The new K5 ran at the same clock speeds that the old SSA/5 series ran at, however this time around we began to see some serious competition for the Cyrix 6x86 and Intel's Pentium. The K5-PR133 provided performance greater than Cyrix's 6x86-PR166+ when running at a clock speed 25% lower, and also gave Intel's Pentium excellent competition when running business applications. The FPU still wasn't up to par with the much more expensive Pentium, however most purchasers of the K5 didn't care...and they still don't! The AMD K5 is not for the die hard Quake fan, and although running games on it isn't unbearable...I wouldn't recommend it, at least not without a Monster 3D.

Second Generation AMD K5 Series Microprocessor
Chip Name P-Rating Clock Speed Bus Speed x Multiplier
AMD K5-PR166 PR166 116.5MHz 66 MHz x 2.5 (internal - 1.75x)

The final link in the K5 chain, although a year overdue, is the AMD K5-PR166. The K5-PR166 is a great chip, running at a mere 116.5MHz, it can easily outperform the Pentium 166 in applications requiring integer operations alone (i.e. business applications). Where did the odd clock speed come from? Since no motherboard on this planet supports the 1.75x clock multiplier required by the K5-PR166, AMD used an internal clock multiplier setting of 1.75x which would activate every time an external 2.5x setting was used.

Overclocking with the previous SSA/5's and K5's was nearly impossible, since they, like the Cyrix 6x86, produce enormous amounts of heat. However many reports of successful overclocking experiences with the K5-PR166 began to emerge soon after its release. How? From my tests on the AMD K5-PR166, it can be taken up to 75 x 1.75 and even 83 x 1.75 (although 83 x 1.75 is not very stable) with extreme cooling and a well ventilated case.

Overall the K5 is a great processor, a bit hot, but still useful for business applications. With all of the more expensive chips becoming popular, many people let their want for the fastest chip crowd their judgement for what they really need. If all you run is MS Word, Netscape, and a game or two do not spend $700 on a Pentium II!!! Shell out about $79 for a K5 and get a Monster 3D if you really want to play games on your system.

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