Editing CPU cache (section)

==History==
[[File:NeXTcube motherboard.jpg|thumb|[[Motherboard]] of a [[NeXTcube]] computer (1990). At the lower edge of the image left from the middle, there is the CPU [[Motorola 68040]] operated at 25 [[MHz]] with two separate level 1 caches of 4 KiB each on the chip, one for the instructions and one for data. The board has no external L2 cache.]]
Early examples of CPU caches include the [[Titan (1963 computer)|Atlas 2]]<ref>{{cite web|last=Landy|first=Barry|url=http://www.chilton-computing.org.uk/acl/technology/atlas50th/p005.htm|title=Atlas 2 at Cambridge Mathematical Laboratory (and Aldermaston and CAD Centre)|date=November 2012|quote=Two tunnel diode stores were developed at Cambridge; one, which worked very well, speeded up the fetching of operands, the other was intended to speed up the fetching of instructions. The idea was that most instructions are obeyed in sequence, so when an instruction was fetched that word was placed in the slave store in the location given by the fetch address modulo 32; the remaining bits of the fetch address were also stored. If the wanted word was in the slave it was read from there instead of main memory. This would give a major speedup to instruction loops up to 32 instructions long, and reduced effect for loops up to 64 words.}}</ref> and the [[IBM System/360 Model 85]]<ref>{{cite web|url=http://www.bitsavers.org/pdf/ibm/360/functional_characteristics/A22-6916-1_360-85_funcChar_Jun68.pdf|title=IBM System/360 Model 85 Functional Characteristics|publisher=[[IBM]]|id=A22-6916-1|date=June 1968}}</ref><ref>{{cite journal|url=https://www.andrew.cmu.edu/course/15-440/assets/READINGS/liptay1968.pdf|last=Liptay|first=John S.|title=Structural aspects of the System/360 Model 85 - Part II The cache|journal=IBM Systems Journal|date=March 1968|volume=7|issue=1|pages=15–21|doi=10.1147/sj.71.0015}}</ref> in the 1960s. The first CPUs that used a cache had only one level of cache; unlike later level 1 cache, it was not split into L1d (for data) and L1i (for instructions). Split L1 cache started in 1976 with the [[IBM 801]] CPU,<ref>{{cite journal|url=http://home.eng.iastate.edu/~zzhang/courses/cpre585-f03/reading/smith-csur82-cache.pdf|title=Cache Memories|last=Smith |first=Alan Jay|journal=Computing Surveys|volume=14|issue=3|date=September 1982|pages=473–530|doi=10.1145/356887.356892|s2cid=6023466}}</ref><ref>{{cite journal|title=Altering Computer Architecture is Way to Raise Throughput, Suggest IBM Researchers|journal=[[Electronics (magazine)|Electronics]]|volume=49|issue=25|date=December 1976|pages=30–31}}</ref> became mainstream in the late 1980s, and in 1997 entered the embedded CPU market with the ARMv5TE. In 2015, even sub-dollar [[System on a chip|SoCs]] split the L1 cache. They also have L2 caches and, for larger processors, L3 caches as well. The L2 cache is usually not split, and acts as a common repository for the already split L1 cache. Every core of a [[multi-core processor]] has a dedicated L1 cache and is usually not shared between the cores. The L2 cache, and higher-level caches, may be shared between the cores. L4 cache is currently uncommon, and is generally [[dynamic random-access memory]] (DRAM) on a separate die or chip, rather than [[static random-access memory]] (SRAM). An exception to this is when [[eDRAM]] is used for all levels of cache, down to L1. Historically L1 was also on a separate die, however bigger die sizes have allowed integration of it as well as other cache levels, with the possible exception of the last level. Each extra level of cache tends to be bigger and optimized differently.

Caches (like for RAM historically) have generally been sized in powers of: 2, 4, 8, 16 etc. [[Kibibyte|KiB]]; when up to [[Mebibyte|MiB]] sizes (i.e. for larger non-L1), very early on the pattern broke down, to allow for larger caches without being forced into the doubling-in-size paradigm, with e.g. [[Intel Core 2 Duo]] with 3&nbsp;MiB L2 cache in April 2008. This happened much later for L1 caches, as their size is generally still a small number of KiB. The [[IBM zEC12 (microprocessor)|IBM zEC12]] from 2012 is an exception however, to gain unusually large 96&nbsp;KiB L1 data cache for its time, and e.g. the [[IBM z13 (microprocessor)|IBM z13]] having a 96&nbsp;KiB L1 instruction cache (and 128&nbsp;KiB L1 data cache),<ref>{{cite web|last1=White|first1=Bill|last2=De Leon|first2=Cecilia A.|display-authors=etal |url=https://www.redbooks.ibm.com/redbooks/pdfs/sg248250.pdf|title=IBM z13 and IBM z13s Technical Introduction|page=20|date=March 2016|publisher=IBM}}</ref> and Intel [[Ice Lake (microprocessor)|Ice Lake]]-based processors from 2018, having 48&nbsp;KiB L1 data cache and 48&nbsp;KiB L1 instruction cache. In 2020, some [[Intel Atom]] CPUs (with up to 24 cores) have (multiple of) 4.5&nbsp;MiB and 15&nbsp;MiB cache sizes.<ref>{{Cite press release|url=https://www.intel.com/content/www/us/en/newsroom/news/product-fact-sheet-accelerating-5g-network-infrastructure-core-edge.html|publisher=Intel Corporation |date=25 February 2020|title=Product Fact Sheet: Accelerating 5G Network Infrastructure, from the Core to the Edge|website=Intel Newsroom|quote=L1 cache of 32KB/core, L2 cache of 4.5MB per 4-core cluster and shared LLC cache up to 15MB.|language=en-US|access-date=2024-04-18}}</ref><ref>{{Cite web|url=https://www.anandtech.com/show/15544/intel-launches-atom-p5900-a-10nm-atom-for-radio-access-networks|title=Intel Launches Atom P5900: A 10nm Atom for Radio Access Networks|last=Smith|first=Ryan|website=AnandTech |access-date=2020-04-12}}</ref>