Editing Disk storage (section)

== Background ==
[[Sound|Audio]] information was originally recorded by analog methods (see [[Sound recording and reproduction]]). Similarly the [[Laserdisc|first video disc]] used an analog recording method. In the music industry, analog recording has been mostly replaced by digital [[optical]] technology where the data is recorded in a digital format with optical information.

The first commercial digital disk storage device was the [[IBM 350]] which shipped in 1956 as a part of the [[IBM 305 RAMAC]] computing system. The [[random-access memory|random-access]], low-density storage of disks was developed to complement the already used [[sequential access|sequential-access]], high-density storage provided by [[tape drive]]s using [[magnetic tape]]. Vigorous innovation in disk storage technology, coupled with less vigorous innovation in tape storage, has reduced the difference in acquisition cost per [[terabyte]] between disk storage and tape storage; however, the total cost of ownership of data on disk including power and management remains larger than that of tape.<ref>{{cite web 
|url= http://users.sdsc.edu/~mcdonald/content/papers/dt_cost.pdf |archive-url=https://web.archive.org/web/20080725004034/http://users.sdsc.edu/~mcdonald/content/papers/dt_cost.pdf |archive-date=2008-07-25 |url-status=live
|title= Disk and Tape Storage Cost Models 
|last= Richard L. Moore
|date= May 3, 2007
|publisher= San Diego Supercomputer Center, UCSD
|access-date=20 February 2013|display-authors=etal}}</ref>

Disk storage is now used in both computer storage and consumer electronic storage, e.g., [[CD-ROM|audio CD]]s and video discs ([[Video CD|VCD]], [[DVD]] and [[Blu-ray]]).

Data on modern disks is stored in fixed length blocks, usually called [[Disk sector|sectors]] and varying in length from a few hundred to many thousands of bytes.  Gross disk drive capacity is simply the number of disk surfaces times the number of blocks/surface times the number of bytes/block.  In certain [[Count key data#IBM.27s CKD DASD subsystems|legacy IBM CKD drives]] the data was stored on magnetic disks with variable length blocks, called records; record length could vary on and between disks.  Capacity decreased as record length decreased due to the necessary gaps between blocks.