{{Short description|Data-storage devices}} In early computers '''drum storage''' consisted of a large metal cylinder coated on the outside surface with a ferromagnetic recording material, to provide random access for stored data. Drums were later largely replaced by the hard disk drive.

Drums were used as main memory by IBM in computers including the IBM 305 and IBM 650; IBM also offered drum devices as secondary storage for the 700/7000 series and System/360 series of computers.

==IBM 731== The '''IBM 731''' is a discontinued storage unit used on the IBM 701.<ref>{{cite manual | title = Principles Of Operation Type 701 and Associated Equipment | year = 1953 | url = http://www.bitsavers.org/pdf/ibm/701/24-6042-1_701_PrincOps.pdf | access-date = May 22, 2021 | publisher = IBM Corporation }} </ref> It has a storage capacity of 2,048 36-bit words (9,216 8-bit bytes).

==IBM 732== The '''IBM 732''' is a discontinued storage unit used on the IBM 702.<ref>{{cite manual | title = Type 702 Preliminary Manual Of Instruction | year = 1954 | access-date = May 22, 2021 | url = http://www.bitsavers.org/pdf/ibm/702/22-6173-1_702prelim_Feb56.pdf | publisher = IBM Corporation }} </ref> It has a storage capacity of 60,000 6-bit characters (45,000 8-bit bytes).

==IBM 733== The '''IBM 733''' is a discontinued storage unit used on the IBM 704<ref>{{cite manual | title = IBM 704 electronic data-processing machine | year = 1955 | url = http://www.bitsavers.org/pdf/ibm/704/24-6661-2_704_Manual_1955.pdf | access-date = May 22, 2021 | publisher = IBM Corporation }} </ref> and IBM 709. It has a storage capacity of 8192 36-bit words (36,864 8-bit bytes).

==IBM 734== The '''IBM 734''' is a discontinued storage unit used on the IBM 705<ref>{{cite manual | title = 705 Data Processing System Reference Manual | year = 1959 | url = http://www.bitsavers.org/pdf/ibm/705/A22-6506-0_705_Reference_Man_May59.pdf | access-date = May 22, 2021 }} </ref> It has a storage capacity of 60,000 6-bit characters (45,000 8-bit bytes).

== IBM 7320 == The '''IBM 7320''' is a discontinued storage unit manufactured by IBM which was announced on December 10, 1962<ref>{{cite web |last1=IBM Corporation |title=DPD chronology |url=https://www.ibm.com/ibm/history/exhibits/dpd50/dpd50_chronology2.html |website=IBM Archives |access-date=Dec 6, 2019}}</ref> for the IBM 7090 and 7094 computer systems, was retained for the earliest System/360 systems as a count key data device, and was discontinued in 1965. The 7320 is a vertically mounted head-per-track device with 449 tracks, 400 data tracks, 40 alternate tracks, and 9 clock/format tracks. The rotational speed is 3,490 rpm, so the average rotational delay is 8.6 milliseconds.<ref name="IBM 7320">{{cite manual | title = IBM 7320 Drum Storage | year = 1962 | url = http://bitsavers.org/pdf/ibm/7090/G22-6717_7320_7631_1962.pdf | series = 7090/7094 Data Processing Systems | publisher = IBM Corporation }} </ref>

Attachment to a 709x system is through an IBM 7909 Data Channel and an IBM 7631 File Control unit, which can attach up to five random-access storage units: a mix of 7320, 1301, and 1302 DASD. One or two 7631 controllers can attach to a computer system, but the system can still attach only a total of five DASD.<ref name="IBM 7320" /> When used with a 709x, a track holds 2,796 6-bit characters, and a 7320 unit holds 1,118,400 characters.{{efn|The actual capacity depends on the contents of the format track, but with full track formatting it is 2,796 6-bit characters/track and 1,118,400 characters/unit.}} Data transfer rate is 202,800 characters per second.<ref name="IBM 7320" />

The 7320 attaches to a System/360 computer through a channel and an IBM 2841 Storage Control unit. Each 2841 can attach up to eight 7320 devices. When used with System/360, a track holds 2,081 8-bit bytes, and a 7320 unit holds 878,000 bytes. Data transfer rate is 135,000 bytes per second.<ref>{{cite manual | 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 | edition = First | date = | chapter = IBM 7320 Drum Storage | section-url = http://bitsavers.org/pdf/ibm/2841/A26-5988-0_2841_2311_2321_7320_Descr.pdf#page=44 | page = 41 | quote = The drum is divided into 400 data tracks; each track has a read/write head and may contain up to 2,081 bytes of data. The maximum data transfer rate is 135 thousand bytes per second. | url = http://bitsavers.org/pdf/ibm/2841/A26-5988-0_2841_2311_2321_7320_Descr.pdf | ref = {{sfnref|IBM 7320}} | access-date = Dec 6, 2019 | series = Systems Reference Library | publisher = IBM }} </ref>

The 7320 was superseded by the IBM 2301 in mid-1966.<ref>{{Cite book|title=IBM's 360 and Early 370 Systems|last1=Pugh|first1=Emerson W.|last2=Johnson|first2=Lyle R.|last3=Palmer|first3=John H.|publisher=MIT Press|year=1991|isbn=0-262-16123-0|location=|page=[https://archive.org/details/ibms360early370s0000pugh/page/272 272] |url=https://archive.org/details/ibms360early370s0000pugh|url-access=registration|author-link=Emerson Pugh}}</ref><ref>{{cite journal |last1=Office of Naval Research |journal=Digital Computer Newsletter |date=October 1964 |volume=16 |issue=4 |title=IBM System 360 |pages=7–8 |url=https://books.google.com/books?id=DR8pjs4SVR4C&pg=RA7-PA8 |publisher = Office of Naval Research - Mathematical Sciences Division |access-date=Dec 6, 2019 }} </ref>

==IBM 2301== The '''IBM 2301''' is a magnetic drum storage device introduced in the late 1960s to "provide large capacity, direct access storage for IBM System/360 Models 65, 67, 75, or 85." The vertically mounted drum rotates at around 3,500 revolutions per minute, and has a head-per-track access mechanism and a capacity of 4 MB. The 2301 has 800 physical tracks; four physical tracks make up one logical track which is read or written as a unit. The 200 logical tracks have 20,483 bytes each. The average access time is 8.6 ms, and the data transfer rate is 1,200,000 bytes per second. The 2301 attaches to a System/360 via a selector channel and an IBM 2820 Storage Control Unit, which can control up to four 2301 units.<ref>{{cite manual | title = IBM System/360 Component Descriptions -- 2820 Storage Control and 2301 Drum Storage | id = A22-6895-2 | pages = 30–31 | edition = Third | date = September 1968 | section = IBM 2301 Drum Storage | section-url = http://bitsavers.org/pdf/ibm/2820/A22-6895-2_2820_2301_Component_Descr_Sep69.pdf#page=38 | url = http://bitsavers.org/pdf/ibm/2820/A22-6895-2_2820_2301_Component_Descr_Sep69.pdf | access-date = April 18, 2021 | ref = {{sfnref|2301}} | series = Systems Reference Library | publisher = IBM Corporation }} </ref>

==IBM 2303== The '''IBM 2303''' is a magnetic drum storage device with the same physical specifications as the IBM 2301. The difference is that the 2303 reads and writes one physical track at a time, rather than the four in the 2301, reducing the data transfer rate to 312,500 bytes per second. The 2303 attaches to System/360 through a channel and an IBM 2841 Storage Control Unit, which can attach up to two 2303 units.<ref>{{cite manual | title = IBM System/360 Component Descriptions - 2841 and Associated DASD | id = GA26-5988-7 | date = December 1969 | edition = Eighth | section = IBM 2303 Drum Storage | section-url = http://bitsavers.org/pdf/ibm/2841/GA26-5988-7_2841_DASD_Component_Descr_Dec69.pdf#page=77 | pages = 74–76 | quote = Storage capacity: 3.913 million bytes. High speed accessibility: Rotational Delay Only: average 8.6ms. Fast data transfer to the processor: 303,800 bytes per second. | url = http://bitsavers.org/pdf/ibm/2841/GA26-5988-7_2841_DASD_Component_Descr_Dec69.pdf | ref = {{sfnref|IBM 2303}} | access-date = April 17, 2021 | series = Systems Reference Library | publisher = IBM Corporation }} </ref>

==See also== * Drum memory: Drums used as main memory

== Notes == {{Notelist}}

==References== {{Reflist}}

Category:History of computing hardware 7320 Category:Computer storage devices