Editing Computer data storage (section)

{{short description|Storage of digital data readable by computers}}
{{Merge from|Data at rest|discuss=Talk:Computer data storage#Proposed merge of Data at rest into Computer data storage|date=March 2025}}
{{Use dmy dates|date=June 2020}}
{{broader|Data storage}}

[[File:DDR2 ram mounted.jpg|thumb|1&nbsp;[[Gibibyte|GiB]] of [[SDRAM]] mounted in a [[computer]]. An example of ''primary storage''.]]
[[File:IBM DJNA-351520 Hard Disk A.jpg|thumb|15&nbsp;[[Gigabyte|GB]] [[Parallel ATA|PATA]] hard disk drive (HDD) from 1999. When connected to a computer it serves as ''secondary'' storage.]]
[[File:Super DLTtape I.jpg|thumb|160&nbsp;[[Gigabyte|GB]] [[Digital Linear Tape|SDLT]] [[tape cartridge]], an example of ''off-line'' storage. When used within a robotic [[tape library]], it is classified as ''tertiary'' storage instead.]]
[[File:Sony_CRX310S-Internal-PC-DVD-Drive-Opened.jpg|thumb|Read/Write DVD drive with cradle for media extended]]

'''Computer data storage''' or '''digital data storage''' is a technology consisting of [[computer]] components and [[Data storage|recording media]] that are used to retain [[digital data]]. It is a core function and fundamental component of computers.<ref name="Patterson">{{Cite book |title=Computer organization and design: The hardware/software interface |last1=Patterson |first1=David A. |last2=Hennessy |first2=John L. |date=2005 |publisher=[[Morgan Kaufmann Publishers]] |isbn=1-55860-604-1 |edition=3rd |location=[[Amsterdam]] |oclc=56213091 |url-access=registration |url=https://archive.org/details/isbn_9781558606043 }}</ref>{{rp|15–16}}

The [[central processing unit]] (CPU) of a computer is what manipulates data by performing computations. In practice, almost all computers use a [[storage hierarchy]],<ref name="Patterson"/>{{rp|468–473}} which puts fast but expensive and small storage options close to the CPU and slower but less expensive and larger options further away. Generally, the fast{{efn|Most contemporary computers use volatile technologies (which lose data when power is off); early computers used both volatile and persistent technologies.}} technologies are referred to as "memory", while slower persistent technologies are referred to as "storage".

Even the first computer designs, [[Charles Babbage]]'s [[Analytical Engine]] and [[Percy Ludgate]]'s Analytical Machine, clearly distinguished between processing and memory (Babbage stored numbers as rotations of gears, while Ludgate stored numbers as displacements of rods in shuttles). This distinction was extended in the [[Von Neumann architecture]], where the CPU consists of two main parts: The [[control unit]] and the [[arithmetic logic unit]] (ALU). The former controls the flow of data between the CPU and memory, while the latter performs arithmetic and [[Bitwise operation|logical operations]] on data.