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The AMD 5k86 Processor
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The 5k86 is AMD's 5th generation x86 implementation, introduced in March 1996. The processor, later renamed to K5, was eagerly awaited and it was hoped that it would provide a viable alternative to the Pentium early in the Pentium's life cycle. Unfortunately, AMD delivered the processor over a year late and at much lower clock speeds than had been originally anticipated. As a result instead of being the "Pentium killer" AMD had hoped for, the K5 was positioned as a low-cost Pentium alternative.
The K5 is, internally, a very advanced processor, the most advanced of the fifth-generation chips. Internally it is more comparable to the Pentium Pro. It is an x86 translation/emulation processor, decoding x86 instructions into RISC-like microinstructions and executing them on a 6-pipeline internal core. This allows the K5 to achieve higher performance than a Pentium of the same speed. |
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The AMD K5 Processor
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The K5 was developed by AMD to compete with Intel's Pentium microprocessor range. Introduced in 1996 almost 2 years late,
AMD's problems were compounded by being unable to manufacture the chip at the clock speeds originally projected. In its favor, the K5 did at least offer good
x86 compatibility. All models had 4.3 million transistors on-chip. No K5 supported MMX instructions. Internally ambitious, it was closer to a
Pentium Pro than a Pentium, based upon an internal highly parallel RISC processor architecture with an x86 decoding front-end.
Improvements and differences to the Intel Pentium include:
- Five integer units, which could process instructions out of order, one floating point unit, compared to two units of the Pentium
- The branch target buffer was four times the size of the Pentium's, although not reportedly more accurate
- Register renaming improved parallel performance of the pipelines
- Speculative execution of instructions reduced pipeline stall
- The instruction cache is 16 Kb, double the Pentium
- The primary cache is 4-way set associative instead of the Pentium's 2-way
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 was weak. The low clock rates were due in part to AMD's deficiencies as a manufacturing company in the period. However, 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 project 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. Overall, the chip failed
to deliver, both in terms of raw performance, and financially for AMD.
References:
AMD K5 Tech Docs
AMD-K5 Processor Overview
Byte.com: Next generation: K5
PC Guide
Processor Emporum
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