AMD K5

9/11/2004

The AMD K5 was AMD's initial attempt at a Pentium Class ("Fifth Generation") CPU dating to about 1994. Although the engineering was generally received favorably, the CPUs themselves were shipped about 9 months behind competing Pentiums and were faulted for excessive power consumption (11-16watts) resulting in cooling problems in an era when CPU fans were none too reliable. The K5s consumed 10-15% more power than competing Pentiums. Not all that much, but an issue in a time when CPU cooling was often marginal. Overall, The K5 did not compete effectively with the Pentium, NexGen and Cyrix 6x86. AMD subsequently acquired NexGen and built its later CPUs on the NexGen chip rather than the K5.

The K5 is a superscalar design with two execution units. It is pin compatible with the Pentium Socket 5 and 7 motherboards. The K5 performed somewhat better than Pentiums at the same clock speed, but not enough to overcome the clock speed differential with the Pentium. For example, the fastest K5 at the time the Pentium 166 was shipped was a K5-100.

K5s were shipped at 75, 90, 100 and 116.5MHz clocks. These were Plus rated as equivalent to Pentiums at (100) 120, 133 and 166MHz. Both 60 and 66MHz bus units were shipped. Earlier CPUs used a 1.5x clock multiplier. The last, highest speed, units used a 1.75x clock multiplier. A 133MHz clock unit was announced but never shipped. Clock multipliers are fixed making overclocking difficult. Production shut down in the Summer of 1997 when AMD switched to the NexGen based K6 CPU. All K5s are 3.52 volt CPUs made with 0.35micron technology. They contain about 4.3 million transistors on a 161square mm die.