Microprocessor History – AMD K5, Red Team’s First in-house Architecture

In March of 1996, AMD released their first products based on a totally in-house microarchitecture, the K5. Internally, AMD engineers decided the ‘K’ in K5 would stand for Kryptonite, hinting AMD is the Kryptonite to their competitor Intel. AMD’s K5 CPUs were a big step toward affordable computing.

AMD’s K5 was based upon the development of previous 29000 – 29900 Series integrated circuits, multiple families of RISC-based designs developed from 1988. The K5 microarchitecture featured an early, widely parallel RISC execution engine with an x86 decoder. It’s execution engine was built upon two integer units, an FPU, and a load/store unit. K5 was split into two families, SSA/5 and 5k86. K5 featured a branch prediction unit, and its branch target buffer was massive for its time, being four times larger than K5’s primary competitor, the Intel Pentium. K5 also supported speculative execution and minimized pipeline stalls. Both models of K5, SSA/5, and 5k86 contained a total of 4.3 million transistors.

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Architecturally, AMD’s K5 architecture was much more advanced than Intel’s P5, but the K5 architecture suffered from clock scaling issues.

Similarly to Intel’s Pentium, K5 CPUs could be used in Socket 5 and Socket 7 motherboards.

SSA/5 processors were available on March 27th, 1996. Due to early manufacturing issues, SSA/5 processors had their branch production units disabled and were manufactured on the 500nm process. SSA/5 chips had a die area of 161mm². Two SSA/5 models initially were released. These include the 5k86-P75 and 5k86-P90. Multiple versions of these processors were released under different part numbers with slight variations in maximum temperature. After the release of a third SSA/5 processor on June 17th, 1996, the K5 PR100, all K5 chips were branded under the K5 name with a performance rating (PR) relative to competing Intel Pentiums. The 5k86-P75 became the K5 PR75 and the 5k86-P90 became the K5 PR90. K5 processors branded under the K5 PR system were manufactured on the 350nm process.

The SSA/5 family was AMD’s first attempt to bring affordable computing to the masses. The K5 PR75 was available for $75, K5 PR90 for $90, and the K5 PR100 for $84 due to its later release.

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Model Clock FSB Multiplier Voltage Part Number
5k86-P75 75MHz 50MHz 1.5 3.525V AMD-SSA/5-75ABR
K5 PR75 75MHz 50MHz 1.5 3.525V AMD-K5-PR75ABR
5k86-P90 90MHz 60MHz 1.5 3.525V AMD-SSA/5-90ABQ
K5 PR90 90MHz 60MHz 1.5 3.525V AMD-K5-PR90ABQ
K5 PR100 100MHz 66MHz 1.5 3.525V AMD-K5-PR100ABQ
K5 PR100 100MHz 66MHz 1.5 3.525V AMD-K5-PR100ABR

5k86-based processors were first released on October 7, 1996. 5k86 chips were manufactured on the 350nm process and had their branch prediction units enabled and had a die area of 181mm². 5k86 processors include the K5 PR120, K5 PR133, K5 PR150, K5 PR166, and K5 PR200.

The K5 PR200 was not widely available due to its late announcement, and was only shipped out to reviewers and sold for a brief period of time to avoid cannibalizing sales of AMD’s upcoming K6.

Model Clock FSB Multiplier Voltage Part Number
K5 PR120 90.00MHz 60MHz 1.50 3.525V AMD-K5-PR120ABQ
K5 PR120 90.00MHz 60MHz 1.50 3.525V AMD-K5-PR120ABR
K5 PR133 100.0MHz 66MHz 1.50 3.525V AMD-K5-PR133ABQ
K5 PR133 100.0MHz 66MHz 1.50 3.525V AMD-K5-PR133ABR
K5 PR150 105.0MHz 60MHz 1.75 3.525V AMD-K5-PR150ABR
K5 PR166 116.7MHz 66MHz 1.75 3.525V AMD-K5-PR166ABQ
K5 PR166 116.7MHz 66MHz 1.75 3.525V AMD-K5-PR166ABX
K5 PR166 116.7MHz 66MHz 1.75 3.525V AMD-K5-PR166ABR
K5 PR200 133.0MHz 66MHz 2.00 3.525V AMD-K5-PR200ABX

K5 never made the dent in Intel’s market share as originally intended due to manufacturing delays and design barriers, but K5 did pave the way to K6. K5 was successful, however, and created the ability for AMD to purchase NexGen. With the purchase of NexGen, AMD inherited the engineering talent and existing designs that would later propel AMD to the top with K6, K6-2, and K6-III.

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