Editing AMD K5

{{Short description|Microarchitecture}}
{{Infobox CPU
|name           =AMD  K5
|image          = AMD K5 PR166 Front.jpg
|image_size     = 200px
|caption        = An AMD K5 PR166 microprocessor
|manuf1         = [[AMD]]
|produced-start = March 27, 1996 (SSA/5)<br />October 7, 1996 (5k86)
|produced-end   = 
|model          = SSA/5 Series
|model1         = 5k86 Series
|transistors    = 4.3M 500 [[nanometers|nm]]
|slowest        = 75|slow-unit      = MHz
|fastest        = 133|fast-unit     = MHz
|fsb-slowest    = 50|fsb-slow-unit  = MHz
|fsb-fastest    = 66|fsb-fast-unit  = MHz
|soldby         = 
|sock1          = [[Socket 5]]
|sock2          = [[Socket 7]]
|brand1         = 
|arch           = [[IA-32]]/[[x86]]
|microarch      = K5
|cpuid          =
|code           = 
|numcores       = 1
|l1cache        = 8 KB + 16 KB<br />(data + instructions)
|application    = Desktop, Embedded
|predecessor    = [[Am5x86]]
|successor      = [[AMD K6|K6]]
}}

The '''K5''' is [[AMD]]{{'}}s first [[x86]] processor to be developed entirely [[in-house]]. Introduced in March 1996, its primary competition was [[Intel|Intel's]] [[Pentium (original)|Pentium]] [[microprocessor]]. 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==
[[Image:AMDK5Diagram.png|thumb|250px|K5 core diagram]]
The K5 was based upon an internal highly parallel [[RISC]] processor architecture with an x86 decoding front-end.<ref>{{cite book |url=http://bitsavers.org/components/amd/x86/K86/18524C_K5_Processor_Technical_Reference_Manual_Nov96.pdf |title=AMD-K5 Processor Technical Reference Manual |date=November 1996 |publisher=AMD}}</ref> 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]]s, with five integer units that could process instructions [[Out-of-order execution|out of order]] and one floating-point unit. The [[branch target buffer]] was four times the size of the Pentium's and [[register renaming]] helped overcome register dependencies.<ref>{{cite web |url=http://datasheets.chipdb.org/upload/Unzlbunzl/AMD/18522F%20AMD-K5.pdf |title=AMD-K5 Processor Data Sheet |date=January 1997 |publisher=AMD}}</ref> The chip's [[speculative execution]] of instructions reduced pipeline stalls. It had a 16&nbsp;KB four-way [[CPU cache#Associativity|set-associative]] instruction cache and an 8&nbsp;KB data cache. The floating-point divide and square-root microcode were mechanically proven.<ref>{{cite journal |first1=J. Strother |last1=Moore |first2=Thomas W. |last2=Lynch |first3=Matt |last3=Kaufmann |title=A Mechanically Checked Proof of the AMD5K86TM Floating-Point Division Program |journal=[[IEEE Transactions on Computers]] |volume=47 |issue=9 |date=September 1998 |pages=913–926 |publisher=[[IEEE Computer Society]] |location=Washington, DC, USA |doi=10.1109/12.713311}}</ref><ref>{{cite journal |first=David M. |last=Russinoff |title=A Mechanically Checked Proof of Correctness of the AMD K5 Floating Point Square Root Microcode |journal=Formal Methods in System Design |volume=14 |issue=1 |date=January 1999 |pages=75–125 |publisher=[[Kluwer Academic Publishers]] |location=Hingham, MA, USA |doi=10.1023/A:1008669628911 |s2cid=22941018}}</ref>
The floating-point transcendental instructions were implemented in hardware and were faithful to true mathematical results for all operands.<ref>{{cite conference |first1=T. |last1=Lynch |first2=A. |last2=Ahmed |first3=M. |last3=Schulte |first4=T. |last4=Callaway |first5=R. |last5=Tisdale |title=The K5 Transcendental Functions |book-title=Proceedings of the 12th Symposium on Computer Arithmetic |date=19–21 July 1995 |pages=163–170 |publisher=[[IEEE Computer Society]] |location=Washington, DC, USA |isbn=0-8186-7089-4 |doi=10.1109/ARITH.1995.465368}}</ref>

==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]],{{Clarify|date=March 2012}} it was slower than that of the Pentium, although 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 ==
{{empty section|date=March 2023}} <!-- Template:AMD x86 CPU features was deleted per oldid=1142398499#Template:AMD_x86_CPU_features -->

== Models ==
{{Main|List of AMD K5 processors}}
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.<ref>{{cite web |url=http://alasir.com/x86ref/index2.html |title=X86 CPU Reference (Part 2) |website=alasir.com |access-date=12 January 2022 |archive-url=https://web.archive.org/web/20170726175647/http://alasir.com/x86ref/index2.html |archive-date=26 July 2017 |url-status=dead}}</ref><ref>{{cite web | url=https://wccftech.com/microprocessor-history-amd-k5/ | title=Microprocessor History - AMD K5 | date=May 2019 }}</ref> The "SSA/5" line ran from 75 to 100&nbsp;MHz; the "5k86" line ran from 90 to 133&nbsp;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&nbsp;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===
[[Image:AMD5k86-P90 SSA5-90ABQ.jpg|thumb|AMD 5K86-P90 (SSA/5)]]
[[Image:AMD_K5_PR75_die.JPG|thumb|AMD K5 PR75 (SSA/5) die shot]]
* Sold as '''5K86''' P75 to P100, later as '''K5''' PR75 to PR100
* 4.3 million transistors in 500 or 350&nbsp;nm
* L1-Cache: 8 + 16 KB (data + instructions)
* [[Socket 5]] and [[Socket 7]]
* VCore: 3.52&nbsp;V
* [[Front side bus]]: 50 (PR75), 60 (PR90), 66&nbsp;MHz (PR100)
* First release: March 27, 1996
* Clockrate: 75, 90, 100&nbsp;MHz

===5k86===
[[File:AMD K5 die2.JPG|thumb|AMD K5 PR150 (5k86) die shot]]
* Sold as '''K5''' PR120 to PR166; later PR200
* 4.3 million transistors in 350&nbsp;nm
* L1-Cache: 8 + 16 KB (data + instructions)
* [[Socket 5]] and [[Socket 7]]
* VCore: 3.52&nbsp;V
* [[Front side bus]]: 60 (PR120/150), 66&nbsp;MHz
* First release: October 7, 1996
* Clockrate: 90 (PR120), 100 (PR133), 105 (PR150), 116.6 (PR166), 133&nbsp;MHz (PR200)

==References==
{{Reflist}}

==Further reading==

* Gwennap, Linley (25 March 1996). "AMD Ships Pentium Competitor". ''[[Microprocessor Report]]''.
* Slater, Michael (24 October 1994). "AMD's K5 Designed to Outrun Pentium". ''[[Microprocessor Report]]''.
* Slater, Michael (8 May 1995). "AMD K5 Volume Slips into 1996". ''[[Microprocessor Report]]''.

==External links==
{{Commons category}}
*[https://web.archive.org/web/20070405230805/https://www.amd.com/us-en/Processors/ProductInformation/0,,30_118_1260_1264,00.html AMD: AMD-K5 Processor Overview]
*[https://web.archive.org/web/20190206062815/http://www.pcguide.com/ref/cpu/fam/g5K5-c.html Technical overview of the K5 series]
*[http://www.cpushack.com/chippics/AMD/K5/ Pictures of K5 chips at CPUShack.com]
*[https://web.archive.org/web/20050308184007/http://www.zen26266.zen.co.uk/AMD-K5.htm The AMD K5, a much underrated chip]
* [https://web.archive.org/web/20050524105625/http://balusc.xs4all.nl/ned/har-cpu-amd-k5.php AMD K5 technical specifications]

{{AMD processors}}

[[Category:AMD x86 microprocessors|K05]]
[[Category:AMD microarchitectures|K05]]
[[Category:X86 microarchitectures]]
[[Category:Computer-related introductions in 1996]]