The K5 is AMD's first x86 processor to be developed entirely in-house. Introduced in March 1996, its primary competition was Intel's

Pentium Pentium is a brand used for a series of x86 architecture-compatible microprocessors produced by Intel. The original Pentium processor from which the brand took its name was first released on March 22, 1993. After that, the Pentium II and P ...

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...

. The K5 was an ambitious design, closer to a Pentium Pro than a Pentium regarding technical solutions and internal architecture. However, the final product was closer to the Pentium regarding performance, although faster clock-for-clock compared to the Pentium.

Technical details

The K5 was based upon an internal highly parallel Am29000

RISC In computer engineering, a reduced instruction set computer (RISC) is a computer designed to simplify the individual instructions given to the computer to accomplish tasks. Compared to the instructions given to a complex instruction set comp ...

processor architecture with an x86 decoding front-end. The K5 offered good x86 compatibility and the in-house-developed test suite proved invaluable on later projects. All models had 4.3 million

transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...

s, with five integer units that could process instructions out of order and one floating-point unit. The

branch target buffer In computer architecture, a branch target predictor is the part of a processor that predicts the target of a taken conditional branch or an unconditional branch instruction before the target of the branch instruction is computed by the executio ...

was four times the size of the Pentium's and

register renaming In computer architecture, register renaming is a technique that abstracts logical registers from physical registers. Every logical register has a set of physical registers associated with it. When a machine language instruction refers to a partic ...

helped overcome register dependencies. The chip's

speculative execution Speculative execution is an optimization technique where a computer system performs some task that may not be needed. Work is done before it is known whether it is actually needed, so as to prevent a delay that would have to be incurred by doing ...

of instructions reduced pipeline stalls. It had a 16 KB four-way set-associative instruction cache and an 8 KB data cache. The floating-point divide and square-root microcode were mechanically proven. The floating-point transcendental instructions were implemented in hardware and were faithful to true mathematical results for all operands.

Performance

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, in part, due to AMD's limitations as a "cutting edge" manufacturing company at the time, and in part due to the design itself, which had many levels of logic for the process technology of the day, hampering clock scaling. Additionally, while the K5's floating-point performance was regarded as superior to that of the

Cyrix 6x86 The Cyrix 6x86 is a line of sixth-generation, 32-bit x86 microprocessors designed and released by Cyrix in 1995. Cyrix, being a fabless company, had the chips manufactured by IBM and SGS-Thomson. The 6x86 was made as a direct competitor to In ...

, it was slower than that of the Pentium, although while offering more reliable transcendental function results. Because it was late to market and did not meet performance expectations, the K5 never gained the acceptance among large computer manufacturers that the earlier Am486 and later AMD K6 enjoyed.

Features

CPU features table

Models

There were two revisions of the K5 architecture, internally called the SSA/5 and the 5k86, both released with the K5 label. The original set of "SSA/5" CPUs had its branch prediction unit disabled and additional internal waitstates added; these issues were remedied with the "5k86", resulting in up to 30% better performance clock for clock. The "SSA/5" line ran from 75 to 100 MHz; 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 suggested equivalence in integer performance 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 nearly align with the release of K6. Since AMD did not want the two chips competing, the K5-PR200 only arrived in small numbers.

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 KB (data + instructions) *

Socket 5 Socket 5 was created for the second generation of Intel P5 Pentium processors operating at speeds from 75 to 133 MHz as well as certain Pentium OverDrive and Pentium MMX processors with core voltage 3.3 V. It superseded the earlier Sock ...

and

Socket 7 Socket 7 is a physical and electrical specification for an x86-style CPU socket on a personal computer motherboard. It was released in June 1995. The socket supersedes the earlier Socket 5, and accepts P5 Pentium microprocessors manufactured by ...

* VCore: 3.52 V * Front side bus: 50 (PR75), 60 (PR90), 66 MHz (PR100) * First release: March 27, 1996 * Clockrate: 75, 90, 100 MHz

5k86

* Sold as K5 PR120 to PR166; later PR200 * 4.3 million transistors in 350 nm * L1-Cache: 8 + 16 KB (data + instructions) *

and

* VCore: 3.52 V * 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)

References

External links

AMD: AMD-K5 Processor OverviewPictures of K5 chips at CPUShack.com

AMD K5 technical specifications
{{DEFAULTSORT:K5 Advanced Micro Devices x86 microprocessors Advanced Micro Devices microarchitectures X86 microarchitectures Computer-related introductions in 1996