Editing Direct-access storage device (section)

==Terminology==
IBM in its 1964 first version of the "IBM System/360 System Summary" used the term ''File'' to collectively described devices now called DASD.  Files provided "random access storage'"<ref name="360Sum">{{cite book |last1=IBM Corporation |title=IBM System/360 System Summary |date=1964 |page=24 |url=http://bitsavers.org/pdf/ibm/360/systemSummary/A22-6810-0_360sysSummary64.pdf |access-date=Aug 7, 2018}}</ref> At the same time IBM's product reference manual described such devices as "direct access storage devices<ref>{{cite book |title=IBM System/360 Component Descriptions - 2841 Storage Control Unit et. al.
 |url=http://www.bitsavers.org/pdf/ibm/2841/A26-5988-0_2841_2311_2321_7320_Descr.pdf |publisher=IBM |date=1964
 |quote=The IBM 2841 Storage Control Unit provides for the attachment of direct access storage devices to the IBM System/360.}}</ref>" without any acronym.

An early public use of the acronym DASD is in IBM's March 1966 manual, "Data File Handbook.<ref>{{cite book
 |title=Data File Handbook |url=http://www.bitsavers.org/pdf/ibm/generalInfo/C20-1638-1_Data_File_Handbook_Mar66.pdf
 |publisher= IBM}} 85 usages.</ref>" The earliest non-IBM use of the acronym DASD found by the "Google ngram viewer" to refer to storage devices dates from 1968.<ref>{{cite news |url=https://books.google.com/books?id=75NRAAAAYAAJ |pages=40–43 |last=Brown |first=Robert  
|title=Cost and Advantages of On-line DP |work=Datamation |agency=Cahners Publishing Company |date=March 1968}}</ref> From then on use of the term grew exponentially until 1990 after which its usage declined substantially.<ref>{{cite web|title="Ngram_chart: occurrences of DASD"
 |url=https://books.google.com/ngrams/graph?content=DASD&year_start=1960&year_end=2019&corpus=26&smoothing=0}}</ref>

Both drums and data cells have disappeared as products, so DASD remains as a synonym of disk, flash and optical devices. Modern DASD used in mainframes only very rarely consist of single disk-drives. Most commonly "DASD" means large [[disk array]]s utilizing [[redundant array of independent disks|RAID]] schemes. Current devices emulate CKD on FBA hardware.