AMD K5

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The K5 was AMD's first x86 processor developed entirely in-house. Its primary competition was Intel's Pentium microprocessor range. The chip was behind schedule when it was introduced in 1995. AMD as a company was in its infancy of microprocessor design, thus a lot of deadlines were missed and there was a lack of manufacturing expertise in scaling designs. The K5's design was ambitious, with the final product coming closer to a Pentium Pro than the Pentium "Classic". The K5 was based upon an internal highly parallel 29k RISC processor architecture with an x86 decoding front-end.

The K5 offered good x86 compatibility. All models had 4.3 million transistors, with five integer units that could process instructions out of order and one floating point unit. The branch target buffer was four times the size of the Pentium's and register renaming improved parallel performance of the pipelines. The chips speculative execution of instructions reduced pipeline stall. It touted an instruction cache of 16 KiB, which was double that of the Pentium. Further, the primary cache was a "4-way" set associative, instead of the Pentium's "2-way" set. Though, the K5 lacked MMX instructions, which Intel started offering in its Pentium MMX processors that were launched in early 1997. The K5's one floating point unit was lacking, as the Pentium offered two.

The K5 project represented an early chance for AMD to take technical leadership from Intel. Although the chip addressed the right design concepts, the actual engineering implementation had its issues. The low clock rates were due in part to AMD's infancy as a manufacturing company at the time. Having a branch prediction unit four times the size of the Pentium, yet reportedly not delivering superior performance is an example of how the actual implementation fell short of the projects goals. Additionally, while the K5's floating point performance was better than that of the Cyrix 6x86, it was weaker than that of the Pentium. Because it was late to market and did not meet performance expectations, the K5 never gained the acceptance among large computer manufacturers that the Am486 and AMD K6 enjoyed.

There were two sets of K5 processors, internally called the SSA/5 and the 5k86, both released with the K5 label. The "SSA/5" line ran from 75 to 100 MHz (5K86 P75 to P100, later K5 PR-75 to PR100); the "5k86" line ran from 90 to 133 MHz. However, AMD used what it called a PR rating, or performance rating, to label the chips according to their equivalence to a Pentium of that clock speed. Thus, a 116 MHz chip from the second line was marketed as the "K5 PR166". Manufacturing delays caused the PR200's arrival to unfortunately nearly align with the release of K6. Since AMD did not want the two chips competing, the K5-PR200 only arrived in small numbers. Enthusiasts have speculated that many PR200 chips were sold as PR166, because of easy overclocking with later PR166 chips.^[1]

[edit] Models

[edit] SSA/5

• Sold as 5K86 P75 to P100, later as K5 PR75 to PR100
• 4.3 million Transistors in 500 or 350 nm
• L1-Cache: 8 + 16 KiB (Data + Instructions)
• Socket 5 and Socket 7
• VCore: 3.52V
• Front side bus: 50 (PR75), 60 (PR90), 66 MHz (PR100)
• First release: March 27, 1996
• Clockrate: 75, 90, 100 MHz

[edit] 5k86

• Sold as K5 PR120 to PR166 (PR200)
• 4.3 million Transistors in 350 nm
• L1-Cache: 8 + 16 KiB (Data + Instructions)
• Socket 5 and Socket 7
• VCore: 3.52V
• Front side bus: 60 (PR120/150), 66 MHz
• First release: October 7, 1996
• Clockrate: 90 (PR120), 100 (PR133), 105 (PR150), 116.6 (PR166), 133 MHz (PR200)

[edit] References