IBM drum storage

IBM Drum Storage Devices
Industry	Computer hardware
Founded	1950s
Headquarters	Armonk, United States
Products	IBM 731, IBM 732, IBM 733, IBM 734, IBM 7320, IBM 2301, IBM 2303 drum storage devices

In the era of early computer technology, drum storage referred to a sizable metal cylinder coated with a ferromagnetic layer. These drums were eventually superseded by the hard disk drive.

IBM incorporated drums as main memory in machines like the IBM 305 and IBM 650, and also provided them as secondary storage options for the 700/7000 series and System/360 series computers.

IBM 731

The IBM 731 functioned as a storage device for the IBM 701, offering a capacity of 2,048 words, each 36 bits in length (equivalent to 9,216 bytes).

IBM 732

Designed for the IBM 702, the IBM 732 could store up to 60,000 characters encoded in 6 bits each (totaling 45,000 bytes).

IBM 733

The IBM 733 was utilized in the IBM 704 and IBM 709 systems, capable of holding 8,192 words of 36 bits each (amounting to 36,864 bytes).

IBM 734

Supporting the IBM 705, the IBM 734 accommodated storage for 60,000 six-bit characters (45,000 bytes).

IBM 7320

Introduced in December 1962, the IBM 7320 was tailored for use with the IBM 7090 and IBM 7094 systems. It was later employed on early models of the System/360 as a count key data device before its discontinuation in 1965. Its design featured a vertically oriented head-per-track configuration with a total of 449 tracks—comprising 400 data tracks, 40 alternate tracks, and 9 clock/format tracks—rotating at a speed of 3,490 rpm. This arrangement resulted in an average rotational latency of approximately 8.6 milliseconds.

Connectivity to a IBM 709x system was established through an IBM 7909 Data Channel coupled with an IBM 7631 File Control unit. This setup allowed attachment of up to five random-access storage devices, including combinations of the IBM 7320, IBM 1301, and IBM 1302 DASD units. Systems supported either one or two controllers but never exceeded five DASD units in total. Each track on a IBM 709x held about 2,796 six-bit characters; thus, total capacity reached roughly 1.12 million characters with data transfer rates near 203,000 characters per second.

When connected to System/360 systems, the IBM 2841 Storage Control unit facilitated attachment of up to eight IBM 7320 devices. In this configuration, each track stored up to 2,081 eight-bit bytes; overall capacity was about 878,000 bytes with data transfer speeds up to approximately 135,000 bytes per second.

The IBM 7320 was succeeded by the IBM 2301 around mid-1966.

IBM 2301

The IBM 2301 is a magnetic drum storage device introduced in the late 1960s to deliver high-capacity direct-access storage for IBM System/360 Models 65, 67, 75, and 85. Its vertically mounted drum spins at roughly 3,500 RPM and employs a head-per-track mechanism. The device contains a total of 800 physical tracks; four physical tracks are combined into one logical track that holds up to 20,483 bytes. The average time to access data is approximately 8.6 milliseconds, while its data transfer rate reaches about 1.2 million bytes per second. Connection to System/360 systems is achieved via a selector channel paired with an IBM 2820 Storage Control Unit capable of managing up to four such units.

IBM 2303

The IBM 2303 shares identical physical characteristics with the IBM 2301 but differs by reading and writing only one physical track at a time instead of four. This results in a reduced data transfer rate near 312,500 bytes per second. It connects to System/360 systems through a channel and an IBM 2841 Storage Control Unit that supports up to two IBM 2303 devices.

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