Storage Module Drive (SMD) is a family of storage devices ( hard disk drives) that were first shipped by Control Data Corporation in December 1973 as the CDC 9760 40 MB (unformatted) storage module disk drive.Control Data Corporation Newsletter, Summer 1977 Edition, p. 6 The CDC 9762 80 MB variant was announced in June 1974 and the CDC 9764 150 MB and the CDC 9766 300 MB variants were announced in 1975 (all capacities unformatted). A non-removable media variant family of 12, 24 and 48 MB capacity, the MMD, was then announced in 1976. This family's interface, SMD, derived from the earlier Digital RP0x interface, was documented as

ANSI The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...

Standard X3.91M - 1982, Storage Module Interfaces with Extensions for Enhanced Storage Module Interfaces. The SMD interface is based upon a definition of two flat interface cables ("A" control and "B" data) which run from the disk drive to a controller and then to a computer. This interface allows data to be transferred at 9.6 Mbit/s. The SMD interface was supported by many 8 inch and 14 inch removable and non-removable disk drives. It was mainly implemented on disk drives used with

mainframes A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...

and minicomputers and was later itself replaced by SCSI. Control Data shipped its 100,000th SMD drive in July 1981. By 1983 at least 25 manufacturers had supplied SMD drives,1984 Disk/Trend Report including,

Ampex Ampex is an American electronics company founded in 1944 by Alexander M. Poniatoff as a spin-off of Dalmo-Victor. The name AMPEX is a portmanteau, created by its founder, which stands for Alexander M. Poniatoff Excellence.AbramsoThe History ...

, Century Data Systems,

CDC The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...

, Fujitsu, Hitachi, Micropolis, Pertec, Priam,

NEC is a Japanese multinational information technology and electronics corporation, headquartered in Minato, Tokyo. The company was known as the Nippon Electric Company, Limited, before rebranding in 1983 as NEC. It provides IT and network soluti ...

and

Toshiba , commonly known as Toshiba and stylized as TOSHIBA, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. Its diversified products and services include power, industrial and social infrastructure systems, ...

CDC 976x disk geometry

The CDC 9762 80 MB variant has 5 × 14" platters. The top and bottom platters are guard platters and not used for storage. The top and bottom guard platters are exactly the same size as the data platters, and are usually made from a data platter which had too many errors to be usable as a data platter. The remaining 3 platters give 5 data surfaces and one servo surface for head positioning, being the upper surface of the center platter. The CDC 9766 300 MB variant has 12 × 14" platters. Again the top and bottom platters are guard platters and not used for storage. The remaining 10 platters give 19 data surfaces and one servo surface for head positioning, again being the upper surface of the center platter. Common to both the 80 MB and 300 MB disks, they have 823 cylinders and the servo surface is on one of the central platters. The sector size and sectors per track depend on how the disk is initialized. 34 sectors of 512 data

byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...

s each per track is the configuration used on the

GEC 4000 series The GEC 4000 was a series of 16/ 32-bit minicomputers produced by GEC Computers Ltd in the United Kingdom during the 1970s, 1980s and early 1990s. History GEC Computers was formed in 1968 as a business unit of the GEC conglomerate. It ...

minicomputers. SMD

disk pack Disk packs and disk cartridges were early forms of removable media for computer data storage, introduced in the 1960s. Disk pack A disk pack is a layered grouping of hard disk platters (circular, rigid discs coated with a magnetic data storage ...

s (as the Storage Module itself was most commonly called) required head alignment to assure interchangeability of media between drives.

References

{{Control Data Corporation Computer storage devices Computer storage buses Control Data Corporation hardware