# Universal memory

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{{Short description|Proposed form of computer storage}}
{{More citations needed|date=January 2017}}
{{Memory types}}
'''Universal memory''' refers to a [computer data storage](/source/computer_data_storage) device combining the cost benefits of [DRAM](/source/DRAM), the speed of [SRAM](/source/Static_random_access_memory), the non-volatility of [flash memory](/source/flash_memory) along with infinite durability, and longevity. Such a device, if it ever becomes possible to develop, would have a far-reaching impact on the computer market. Some<ref>{{Cite web|url=https://blocksandfiles.com/2019/12/20/western-digital-sivaram-solid-state-storage/|title=WD: Storage class memory will not replace DRAM or NAND|first=Chris|last=Mellor|date=December 20, 2019|website=Blocks and Files}}</ref> doubt that such a type of memory will ever be possible.

[Computers](/source/Computers), for most of their recent history, have depended on several different data storage technologies simultaneously as part of their operation. Each one operates at a level in the memory hierarchy where another would be unsuitable. A [personal computer](/source/personal_computer) might include a few [megabytes](/source/megabytes) of fast but [volatile](/source/Volatile_memory) and expensive [SRAM](/source/Static_random-access_memory) as the [CPU cache](/source/CPU_cache), several [gigabytes](/source/gigabytes) of slower [DRAM](/source/DRAM) for program memory, and Hundreds of GB to a few TB  of slow but [non-volatile](/source/non-volatile_memory) [flash memory](/source/flash_memory) or "spinning platter" [hard disk drive](/source/hard_disk_drive) for long-term storage.  For example, a university<ref>{{Cite web|url=https://ucsdservicedesk.service-now.com/its|title=UCSD IT Service Portal - Information Technology|website=ucsdservicedesk.service-now.com}}</ref> recommended students entering in 2015–2016 to have a PC with:

::- a CPU with a 4×256&nbsp;KB L2&nbsp;cache, and a 6&nbsp;MB L3&nbsp;cache
::- 16&nbsp;GB DRAM
::- 256&nbsp;GB [solid-state drive](/source/solid-state_drive), and
::- 1&nbsp;TB hard disk drive

Researchers seek to replace these different memory types with one single type to reduce the cost and increase performance. For a memory technology to be considered a universal memory, it would need to have best characteristics of several memory technologies. It would need to:

::- operate very quickly{{snd}}like SRAM cache
::- support a practically unlimited number of read/write cycles{{snd}}like SRAM and DRAM 
::- retain data indefinitely without using power{{snd}}like flash memory and hard disk drives, and 
::- be sufficiently large for common operating systems and application programs, yet affordable{{snd}}like hard disk drives.  <!--<small>''(For 2015, UCSD judged 1&nbsp;TB as "sufficiently large but affordable".)''</small>-->

The last criterion is likely to be satisfied last, as [economies of scale](/source/economies_of_scale) in manufacturing reduce cost. Many types of memory technologies have been explored with the goal of creating a practical universal memory. These include:

* low-voltage, non-volatile, compound-semiconductor memory (demonstrated) <ref>{{Cite web|url=https://www.lancaster.ac.uk/news/-discovery-of-a-holy-grail-with-the-invention-of-universal-computer-memory|title=Discovery of a "Holy Grail" with the invention of universal computer memory|website=www.lancaster.ac.uk}}</ref><ref>{{Cite journal|title=Room-temperature Operation of Low-voltage, Non-volatile, Compound-semiconductor Memory Cells|first1=Ofogh|last1=Tizno|first2=Andrew R. J.|last2=Marshall|first3=Natalia|last3=Fernández-Delgado|first4=Miriam|last4=Herrera|first5=Sergio I.|last5=Molina|first6=Manus|last6=Hayne|date=June 20, 2019|journal=Scientific Reports|volume=9|issue=1|pages=8950|doi=10.1038/s41598-019-45370-1|pmid=31222059|pmc=6586817|bibcode=2019NatSR...9.8950T}}</ref>
* magnetoresistive random-access memory ([MRAM](/source/Magnetoresistive_RAM)) (in development and production)
* [bubble memory](/source/bubble_memory) (1970-1980, obsolete)
* [racetrack memory](/source/racetrack_memory) (currently experimental)
* ferroelectric random-access memory ([FRAM](/source/ferroelectric_RAM)) (in development and production)
* phase-change memory ([PCM](/source/phase-change_memory))
* programmable metallization cell ([PMC](/source/programmable_metallization_cell))
* resistive random-access memory ([RRAM](/source/resistive_random-access_memory))
* [nano-RAM](/source/nano-RAM)
* [memristor](/source/memristor)-based memory<ref>{{cite web|last1=Fink|first1=Martin|title=HP Discover 2014 Barcelona Keynote see 12:11|url=http://new.livestream.com/HewlettPackard/Discover14Barcelona/videos/70213733|website=Youtube|publisher=Hewlett Packard|accessdate=4 December 2014|archive-date=4 February 2015|archive-url=https://web.archive.org/web/20150204022728/http://new.livestream.com/HewlettPackard/Discover14Barcelona/videos/70213733|url-status=dead}}</ref>

Since each memory has its limitations, none of these have yet reached the goals of universal memory.

==References==
{{Reflist}}

Category:Solid-state computer storage media
Category:Computer memory
Category:Non-volatile memory

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Adapted from the Wikipedia article [Universal memory](https://en.wikipedia.org/wiki/Universal_memory) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Universal_memory?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.