Editing IBM System/360 (section)

===Direct access storage devices (DASD)===
{{Further|Direct-access storage device}}[[Image:IBM 2311 memory unit.JPG|thumb|IBM 2311 disk drive]]
{{See also|History of IBM magnetic disk drives#IBM S.2F360 and other IBM mainframe HDDs|l1=IBM S/360 and other IBM mainframe HDDs}}

The first disk drives for System/360 were [[IBM 2302]]s<ref name=GA26-5988/>{{rp|60–65}} and [[IBM 2311]]s.<ref name=GA26-5988/>{{rp|54–58}} The first drum for System/360 was the [[IBM 7320]].<ref name="IBM 7320">{{cite book
 | title      = IBM 7320 Drum Storage
 | id         = G22-6717
 | date       = 1962
 | publisher  = IBM Corporation
 | url        = http://www.bitsavers.org/pdf/ibm/7090/G22-6717_7320_7631_1962.pdf
 | access-date = Dec 6, 2019
 | ref        = IBM 7320
 | mode       = cs2}}</ref><ref name=A26-5988-0>{{cite book
 | title      = IBM System/360 Component descriptions-2841 Storage Control Unit 2302 Disk Storage Models 3 and 4 2311 Disk Storage Drive 2321 Data Cell Drive Model 1 7320 Drum Storage
 | id         = A26-5988-0
 | url        = http://bitsavers.org/pdf/ibm/2841/A26-5988-0_2841_2311_2321_7320_Descr.pdf
 | access-date = Dec 6, 2019
 | ref        = IBM 2841
 | mode       = cs2}}</ref>{{rp|41}}
<!-- I'm getting 404 trying to get to bitsavers - I'd appreciate it if someone could add the information for the 2301 and 2303 manuals. -->

The 156&nbsp;kbit/s 2302 was based on the earlier [[IBM 1302|1302]] and was available as a model 3 with two 112.79&nbsp;MB modules<ref name=GA26-5988/>{{rp|60}} or as a model 4 with four such modules.<ref name=GA26-5988/>{{rp|60}}

The 2311, with a removable [[IBM 1316|1316]] [[disk pack]], was based on the [[IBM 1311]] and had a theoretical capacity of 7.2&nbsp;MB, although actual capacity varied with record design.<ref name=A26-5988-0/>{{rp|31}} (When used with a 360/20, the 1316 pack was formatted into fixed-length 270 byte [[disk sector|sectors]], giving a maximum capacity of 5.4MB.)
 
In 1966, the first [[IBM 2314|2314s]] shipped. This device had up to eight usable disk drives with an integral control unit; there were nine drives, but one was reserved as a spare. Each drive used a removable [[IBM 2316|2316]] disk pack with a capacity of nearly 28&nbsp;MB. The disk packs for the 2311 and 2314 were ''physically'' large by today's standards — e.g., the [[IBM 1316|1316]] disk pack was about {{convert|14|in|cm|abbr=on}} in diameter and had six platters stacked on a central spindle. The top and bottom outside platters did not store data. Data were recorded on the inner sides of the top and bottom platters and both sides of the inner platters, providing 10 recording surfaces. The 10 read/write heads moved together across the surfaces of the platters, which were formatted with 203 concentric tracks. To reduce the amount of head movement (seeking), data was written in a virtual cylinder from inside top platter down to inside bottom platter. These disks were not usually formatted with fixed-sized sectors as are today's hard drives (though this ''was'' done with [[CP/CMS]]). Rather, most System/360 I/O software could customize the length of the data record (variable-length records), as was the case with magnetic tapes.

[[File:IBM 2314 DiskDrives and IBM 2540 CardReader Punch.jpg|thumb|IBM 2314 disk drives and IBM 2540 card reader/punch at the University of Michigan]]

{{Anchor|IBM2301}}Some of the most powerful early System/360s used high-speed head-per-track drum storage devices. The 3,500&nbsp;RPM 2301,<ref>[http://www.columbia.edu/acis/history/drum.html IBM 2301 Drum Storage], Columbia University Computing History</ref> which replaced the 7320, was part of the original System/360 announcement, with a capacity of 4&nbsp;MB. The 303.8&nbsp;kbit/s [[IBM 2303]]<ref name=GA26-5988>{{cite book | publisher = IBM | title = IBM System/360 Component Descriptions – 2841 and Associated DASD | id = GA26-5988-7 | date = December 1969 | version = Eighth Edition | url = http://bitsavers.org/pdf/ibm/28xx/2841/GA26-5988-7_2841_DASD_Component_Descr_Dec69.pdf | access-date = 2012-01-02 | archive-url = https://web.archive.org/web/20111014155354/http://www.bitsavers.org/pdf/ibm/28xx/2841/GA26-5988-7_2841_DASD_Component_Descr_Dec69.pdf | archive-date = 2011-10-14 | url-status = dead}}</ref>{{rp|74–76}} was announced on January 31, 1966, with a capacity of 3.913&nbsp;MB. These were the only drums announced for System/360 and System/370, and their niche was later filled by fixed-head disks.

The 6,000&nbsp;RPM 2305 appeared in 1970, with capacities of 5&nbsp;MB (2305–1) or 11&nbsp;MB (2305–2) per module.<ref>{{cite web| url = http://ed-thelen.org/comp-hist/IBM-ProdAnn/2305.pdf| title = IBM 2305 product announcement}}</ref><ref>{{cite book | publisher = IBM | title = Reference Manual for IBM 2835 Storage Control and IBM 2305 Fixed Head Storage Module | id = GA26-1689-4 | version = Fifth Edition | date = November 1980}}</ref> Although these devices did not have large capacity, their speed and transfer rates made them attractive for high-performance needs. A typical use was overlay linkage (e.g. for OS and application subroutines) for program sections written to alternate in the same memory regions. Fixed-head disks and drums were particularly effective as paging devices on the early virtual memory systems. The 2305, although often called a "drum" was actually a head-per-track disk device, with 12 recording surfaces and a data transfer rate up to 3&nbsp;MB/s.

Rarely seen was the [[IBM 2321 Data Cell]],<ref>[http://www.columbia.edu/acis/history/datacell.html The IBM 2321 Data Cell Drive], Columbia University Computing History</ref> a mechanically complex device that contained multiple magnetic strips to hold data; strips could be randomly accessed, placed upon a cylinder-shaped drum for read/write operations; then returned to an internal storage cartridge. The IBM Data Cell [noodle picker] was among several IBM trademarked "speedy" mass online direct-access storage peripherals (reincarnated in recent years as "virtual tape" and automated tape librarian peripherals). The 2321 file had a capacity of 400&nbsp;MB, at the time when the 2311 disk drive only had 7.2&nbsp;MB. The IBM Data Cell was proposed to fill cost/capacity/speed gap between magnetic tapes—which had high capacity with relatively low cost per stored byte—and disks, which had higher expense per byte. Some installations also found the electromechanical operation less dependable and opted for less mechanical forms of direct-access storage.

The Model 44 was unique in offering an integrated single-disk drive as a standard feature. This drive used the 2315 "ramkit" cartridge and provided 1,171,200 bytes of storage.<ref name="m44-func-char"/>{{rp|11}}