Editing Hard disk drive (section)

=== 1950s–1960s ===
The first production IBM hard disk drive, the [[IBM 350|350 disk storage]], shipped in 1957 as a component of the IBM 305 RAMAC system. It was approximately the size of two large refrigerators and stored five million six-bit characters (3.75 [[megabyte]]s)<ref name="350Cap">{{cite web
|title=Comment: Time Capsule, 1956 Hard Disk
|url=http://www.oracle.com/technetwork/issue-archive/2014/14-jul/o44timecapsule-2219543.html
|quote=IBM 350 disk drive held 3.75&nbsp;MB
|series=Oracle Magazine
|date=July 2014
|access-date=September 19, 2014
|archive-url=https://web.archive.org/web/20140811202917/http://www.oracle.com/technetwork/issue-archive/2014/14-jul/o44timecapsule-2219543.html
|archive-date=August 11, 2014
|url-status=live
}}</ref> on a stack of 52 disks (100 surfaces used).<ref name="ibm-350-dsu">{{cite web|title=IBM Archives: IBM&nbsp;350 disk storage unit|url=https://www-03.ibm.com/ibm/history/exhibits/storage/storage_350.html|publisher=IBM|access-date=July 26, 2015|date=January 23, 2003|archive-url=https://web.archive.org/web/20150617040819/https://www-03.ibm.com/ibm/history/exhibits/storage/storage_350.html|archive-date=June 17, 2015|url-status=dead}}</ref> The 350 had a single arm with two read/write heads, one facing up and the other down, that moved both horizontally between a pair of adjacent platters and vertically from one pair of platters to a second set.<ref name=ibm-650>{{citation
 |   title = IBM 650 RAMAC Manual of Operations
 |      id = 22-6270-3
 | edition = 4th
 |    date = June 1, 1957
 |   quote = Three mechanically independent access arms are provided for each file unit, and each arm can be independently directed to any track in the file.
 | chapter = 355 DISK STORAGE
 |    page = 17
 }}
</ref><ref name=ibm-7070>{{citation
 |   title = IBM Reference Manual 7070 Data Processing System
 |      id = A22-7003-1
 | edition = 2nd
 |    date = January 1960
 |   quote = Each disk-storage unit has three mechanically independent access arms, all of which can be seeking at the same time. 
 | chapter = Disk Storage
 |     chapter-url = https://bitsavers.org/pdf/ibm/7070/A22-7003-01_7070_Reference_Jan60.pdf
 }}
</ref><ref name=ibm-1401>{{citation
 |   title = Reference Manual IBM 1401 Data Processing System
 |      id = A24-1403-5
 |    date = April 1962
 | edition = 6th
 |   quote = The disk storage unit can have two access arms. One is standard and the other is available as a special feature.
 | chapter = IBM RAMAC 1401 System
 |    page = 63
 |     chapter-url = https://bitsavers.org/pdf/ibm/1401/A24-1403-5_1401_Reference_Apr62.pdf
 }}
</ref>  Variants of the IBM 350 were the [[IBM 355]], [[IBM 7300]] and [[IBM 1405]].

In 1961, IBM announced, and in 1962 shipped, the IBM&nbsp;1301 disk storage unit,<ref>{{cite web|url=https://www-03.ibm.com/ibm/history/exhibits/storage/storage_1301.html|title=IBM Archives: IBM 1301 disk storage unit|work=ibm.com|date=January 23, 2003|access-date=June 25, 2015|archive-url=https://web.archive.org/web/20141219183129/http://www-03.ibm.com/ibm/history/exhibits/storage/storage_1301.html|archive-date=December 19, 2014|url-status=dead}}</ref> which superseded
the IBM&nbsp;350 and similar drives. The 1301 consisted of one (for Model 1) or two (for model 2) modules, each containing 25 platters, each platter about {{convert|1/8|inch|mm|adj=on}} thick and {{convert|24|inch|mm}} in diameter.<ref>{{cite web|url=http://www.computermuseum.li/Testpage/DiskPlatter-1301.htm|title=DiskPlatter-1301|work=computermuseum.li|url-status=dead|archive-url=https://web.archive.org/web/20150328161124/http://www.computermuseum.li/Testpage/DiskPlatter-1301.htm|archive-date=March 28, 2015}}</ref> While the earlier IBM disk drives used only two read/write heads per arm, the 1301 used an array of 48{{efn|40 for user data, one for format tracks, 6 for alternate surfaces and one for maintenance.}} heads (comb), each array moving horizontally as a single unit, one head per surface used. [[Cylinder-head-sector|Cylinder-mode]] read/write operations were supported, and the heads flew about 250 micro-inches (about 6&nbsp;μm) above the platter surface. Motion of the head array depended upon a binary adder system of hydraulic actuators which assured repeatable positioning. The 1301 cabinet was about the size of three large refrigerators placed side by side, storing the equivalent of about 21 million eight-bit bytes per module. Access time was about a quarter of a second.

Also in 1962, IBM introduced the [[IBM 1311|model 1311]] disk drive, which was about the size of a washing machine and stored two million characters on a removable [[disk pack]]. Users could buy additional packs and interchange them as needed, much like reels of [[magnetic tape]]. Later models of removable pack drives, from IBM and others, became the norm in most computer installations and reached capacities of 300 megabytes by the early 1980s. Non-removable HDDs were called "fixed disk" drives.

In 1963, IBM introduced the 1302,<ref name="1301Ref">{{cite book
 |     title = IBM 1301, Models 1 and 2, Disk Storage and IBM 1302, Models 1 and 2, Disk Storage with IBM 7090, 7094 and 7094 II Data Processing Systems
 |        id = A22-6785
 |       url = https://bitsavers.org/pdf/ibm/7090/A22-6785_1301_1302_on_709x.pdf
 | publisher = IBM
 }}
</ref> with twice the track capacity and twice as many tracks per cylinder as the 1301. The 1302 had one (for Model 1) or two (for Model 2) modules, each containing a separate comb for the first 250 tracks and the last 250 tracks.

{{Anchor|fixed-head}}Some high-performance HDDs were manufactured with one head per track, ''e.g.'', Burroughs B-475 in 1964, [[History of IBM magnetic disk drives#IBM 2305|IBM&nbsp;2305]] in 1970, so that no time was lost physically moving the heads to a track and the only latency was the time for the desired block of data to rotate into position under the head.<ref>Microsoft Windows NT Workstation 4.0 Resource Guide 1995, Chapter 17 – Disk and File System Basics</ref> Known as fixed-head or head-per-track disk drives, they were very expensive and are no longer in production.<ref name="CHAUDHURI2008">{{Cite book |last=Chaudhuri |first=P. Pal |title=Computer Organization and Design |url=https://books.google.com/books?id=5LNwVRpfkRgC&q=%22fixed+head%22&pg=PA568 |date=April 15, 2008 |publisher=PHI Learning Pvt. Ltd. |isbn=978-81-203-3511-0 |page=568|edition=3rd }}</ref>