The term was coined by IBM to describe devices that allowed random access to data, the main examples being drum memory and hard disk drives.
[citation needed] When the 2321 data cell was discontinued in January 1975,[5] the addressing scheme and the device itself was referred to as CHR or CTR for cylinder-track-record, as the bin number was always 0.
The queued access methods, such as QSAM, are responsible for blocking and deblocking logical records as they are written to or read from external media.
CKD is an acronym for Count Key Data, the physical layout of a block on a DASD device, and should not be confused with BBCCH and CCHHR, which are the addresses used by the channel program.
At the programming level, these devices do not use the traditional CHR addressing, but reference fixed-length blocks by number, much like sectors in mini-computers.
More correctly, the application programmer remains unaware of the underlying storage arrangement, which stores the data in fixed physical block lengths of 512, 1024, 2048, or 4096, depending on the device type.
[7]" The earliest non-IBM use of the acronym DASD found by the "Google ngram viewer" to refer to storage devices dates from 1968.