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|url=https://archive.org/details/computerhardware0000toyw/page/30
}}</ref>
* ''Internal'' – {{dash}}[[Processor register]]s and [[CPU cache|cache]].
* Main – {{dash}}the system [[Random-access memory|RAM]] and controller cards.
* On-line mass storage – {{dash}}Secondary storage.
* Off-line bulk storage – {{dash}}Tertiary and Off-line storage.
This is a general memory hierarchy structuring. Many other structures are useful. For example, a paging algorithm may be considered as a level for [[virtual memory]] when designing a [[computer architecture]], and one can include a level of [[nearline storage]] between online and offline storage.
The number of levels in the memory hierarchy and the performance at each level has increased over time. The type of memory or storage components also change historically.<ref>{{cite web|url=http://www.computerhistory.org/timeline/memory-storage/|title=Memory & Storage – Timeline of Computer History – Computer History Museum|website=www.computerhistory.org}}</ref> For example, the memory hierarchy of an Intel Haswell Mobile<ref>{{cite web|last=Crothers |first=Brooke |url=http://news.cnet.com/8301-13579_3-57609045-37/dissecting-intels-top-graphics-in-apples-15-inch-macbook-pro/ |title=Dissecting Intel's top graphics in Apple's 15-inch MacBook Pro – CNET |publisher=News.cnet.com |access-date=2014-07-31}}</ref> processor circa 2013 is:
* [[Processor register]]s – {{dash}}the fastest possible access (usually 1 CPU cycle). A few thousand bytes in size
* [[CPU cache|Cache]]
** Level 0 (L0) [[Micro-operation|Micro operations]] cache – {{dash}}6,144 bytes (6 KiB{{cn|reason=No source provided for IEC units, sources only use metric units like KB, MB, GB, etc|date=May 2021}}{{Original research inline|certain=y|date=May 2021}})<ref>{{cite web|url=http://www.anandtech.com/show/6355/intels-haswell-architecture/6 |title=Intel's Haswell Architecture Analyzed: Building a New PC and a New Intel |publisher=AnandTech |access-date=2014-07-31}}</ref> in size
** Level 1 (L1) [[Opcode|Instruction]] cache – {{dash}}128 KiB{{cn|reason=No source provided for IEC units, sources only use metric units like KB, MB, GB, etc|date=May 2021}}{{Original research inline|certain=y|date=May 2021}} in size
** Level 1 (L1) Data cache – {{dash}}128 KiB{{cn|reason=No source provided for IEC units, sources only use metric units like KB, MB, GB, etc|date=May 2021}}{{Original research inline|certain=y|date=May 2021}} in size. Best access speed is around 700 [[Gigabyte|GB]]/s<ref name=sisd_qa_f_mem_hsw>{{cite web|url=http://www.sisoftware.co.uk/?d=qa&f=mem_hsw |title=SiSoftware Zone |publisher=Sisoftware.co.uk |access-date=2014-07-31|archive-url=https://web.archive.org/web/20140913231938/http://www.sisoftware.co.uk/?d=qa&f=mem_hsw|archive-date=2014-09-13}}</ref>
** Level 2 (L2) Instruction and data (shared) – {{dash}}1 [[MiB]]{{cn|reason=No source provided for IEC units, sources only use metric units like KB, MB, GB, etc|date=May 2021}}{{Original research inline|certain=y|date=May 2021}} in size. Best access speed is around 200 GB/s<ref name=sisd_qa_f_mem_hsw />
** Level 3 (L3) Shared cache – {{dash}}6 MiB{{cn|reason=No source provided for IEC units, sources only use metric units like KB, MB, GB, etc|date=May 2021}}{{Original research inline|certain=y|date=May 2021}} in size. Best access speed is around 100 GB/s<ref name=sisd_qa_f_mem_hsw />
** Level 4 (L4) Shared cache – {{dash}}128 MiB{{cn|reason=No source provided for IEC units, sources only use metric units like KB, MB, GB, etc|date=May 2021}}{{Original research inline|certain=y|date=May 2021}} in size. Best access speed is around 40 GB/s<ref name=sisd_qa_f_mem_hsw />
* [[Computer memory|Main memory]] ([[Primary storage]]) – {{dash}}[[GiB]]{{cn|reason=No source provided for IEC units, sources only use metric units like KB, MB, GB, etc|date=May 2021}}{{Original research inline|certain=y|date=May 2021}} in size. Best access speed is around 10 GB/s.<ref name=sisd_qa_f_mem_hsw /> In the case of a [[Non-Uniform Memory Access|NUMA]] machine, access times may not be uniform
* [[Disk storage]] ([[Secondary storage]]) – {{dash}}[[Terabyte]]s in size. As of 2017, best access speed is from a consumer [[Solid-state drive|solid state drive]] is about 2000 MB/s<ref>{{cite web|url=http://www.storagereview.com/samsung_960_pro_m2_nvme_ssd_review|title=Samsung 960 Pro M.2 NVMe SSD Review|date=20 October 2016 |publisher=storagereview.com|access-date=2017-04-13}}</ref>
* [[Nearline storage]] ([[Tertiary storage]]) – {{dash}}Up to [[exabytes]] in size. As of 2013, best access speed is about 160 MB/s<ref>{{cite web |url=http://www.lto.org/technology/generations.html |title=Ultrium – LTO Technology – Ultrium GenerationsLTO |publisher=Lto.org |access-date=2014-07-31 |url-status=dead |archive-url=https://web.archive.org/web/20110727052050/http://www.lto.org/technology/generations.html |archive-date=2011-07-27 }}</ref>
* [[Offline storage]]
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