Storage Module Device
Encyclopedia
Storage Module Device was a family of storage devices (hard disk
drives) first shipped by Control Data Corporation
in December 1973 as the CDC 9760 40 MB
(unformatted) storage module disk drive. 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
Standard X3.91M - 1982, Storage Module Interfaces with Extensions for Enhanced Storage Module Interfaces.
The SMD interface was based upon a definition of two flat interface cables ("A" control and "B" data) which ran from the disk drive to a controller and then to a computer. This interface allowed data to be transferred at 9.6 Mbit
/s. The SMD interface was supported by most 8 inch and 14 inch removable and non-removable disk drives. It was mainly implemented on disk drives used with mainframes
and minicomputer
s 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, including, Ampex
, Century Data Systems, CDC
, Fujitsu
, Hitachi
, Micropolis, Pertec, Priam and Toshiba
.
The CDC 9766 300 MB variant has 12 x 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.
Common to both the 80 MB and 300 MB disks, they have 823 cylinders and the servo surface is on one of the center platters. The sector size and sectors per track depend on how the disk is initialized. 34 sectors of 512 data byte
s each per track is the configuration used on the GEC 4000 series
minicomputers.
Drives with exchangeable packs and servo surfaces required the data heads to be aligned with the servo head to allow packs formatted on one drive to be read and written on another compatible drive. Alignment required a special alignment pack, an oscilloscope, an alignment tool that moved the read/write heads, and patience. The alignment pack was sometimes called a CE pack (Customer Engineering), because the pattern generated on the scope looks like a row of alternating C and E characters on their backs. Head alignment needed to be performed after head replacement (usually due to a head crash), and in any case on a periodic basis as part of the routine maintenance required by the drives.
Later drives with exchangeable packs (such as the CDC 8" Lark drives) embedded the servo with the data, and hence didn't use separate servo surfaces and didn't require regular head alignment.
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
drives) first shipped by Control Data Corporation
Control Data Corporation
Control Data Corporation was a supercomputer firm. For most of the 1960s, it built the fastest computers in the world by far, only losing that crown in the 1970s after Seymour Cray left the company to found Cray Research, Inc....
in December 1973 as the CDC 9760 40 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
(unformatted) storage module disk drive. 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
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
RP0x interface, was documented as ANSI
Ansi
Ansi is a village in Kaarma Parish, Saare County, on the island of Saaremaa, Estonia....
Standard X3.91M - 1982, Storage Module Interfaces with Extensions for Enhanced Storage Module Interfaces.
The SMD interface was based upon a definition of two flat interface cables ("A" control and "B" data) which ran from the disk drive to a controller and then to a computer. This interface allowed data to be transferred at 9.6 Mbit
Megabit
The megabit is a multiple of the unit bit for digital information or computer storage. The prefix mega is defined in the International System of Units as a multiplier of 106 , and therefore...
/s. The SMD interface was supported by most 8 inch and 14 inch removable and non-removable disk drives. It was mainly implemented on disk drives used with mainframes
Mainframe computer
Mainframes are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.The term originally referred to the...
and minicomputer
Minicomputer
A minicomputer is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems...
s and was later itself replaced by SCSI
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
.
Control Data shipped its 100,000th SMD drive in July 1981. By 1983 at least 25 manufacturers had supplied SMD drives, including, Ampex
Ampex
Ampex is an American electronics company founded in 1944 by Alexander M. Poniatoff. The name AMPEX is an acronym, created by its founder, which stands for Alexander M. Poniatoff Excellence...
, Century Data Systems, CDC
Control Data Corporation
Control Data Corporation was a supercomputer firm. For most of the 1960s, it built the fastest computers in the world by far, only losing that crown in the 1970s after Seymour Cray left the company to found Cray Research, Inc....
, Fujitsu
Fujitsu
is a Japanese multinational information technology equipment and services company headquartered in Tokyo, Japan. It is the world's third-largest IT services provider measured by revenues....
, Hitachi
Hitachi, Ltd.
is a Japanese multinational conglomerate headquartered in Marunouchi 1-chome, Chiyoda, Tokyo, Japan. The company is the parent of the Hitachi Group as part of the larger DKB Group companies...
, Micropolis, Pertec, Priam and Toshiba
Toshiba
is a multinational electronics and electrical equipment corporation headquartered in Tokyo, Japan. It is a diversified manufacturer and marketer of electrical products, spanning information & communications equipment and systems, Internet-based solutions and services, electronic components and...
.
Disk Geometry
The CDC 9762 80 MB variant has 5 x 14" platters. The top and bottom platters are guard platters and not used for storage. The top guard platter is exactly the same size as the data platters, and is usually made from a data platter which had too many errors to be usable. The bottom guard platter is very slightly larger than the data platters. The remaining 3 platters give 5 data surfaces and one servo surface for head positioning.The CDC 9766 300 MB variant has 12 x 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.
Common to both the 80 MB and 300 MB disks, they have 823 cylinders and the servo surface is on one of the center platters. The sector size and sectors per track depend on how the disk is initialized. 34 sectors of 512 data byte
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
s each per track is the configuration used on the GEC 4000 series
GEC 4000 series
The GEC 4000 was a series of 16/32-bit minicomputers produced by GEC Computers Ltd. of the UK during the 1970s, 1980s and early 1990s.- History :...
minicomputers.
Drives with exchangeable packs and servo surfaces required the data heads to be aligned with the servo head to allow packs formatted on one drive to be read and written on another compatible drive. Alignment required a special alignment pack, an oscilloscope, an alignment tool that moved the read/write heads, and patience. The alignment pack was sometimes called a CE pack (Customer Engineering), because the pattern generated on the scope looks like a row of alternating C and E characters on their backs. Head alignment needed to be performed after head replacement (usually due to a head crash), and in any case on a periodic basis as part of the routine maintenance required by the drives.
Later drives with exchangeable packs (such as the CDC 8" Lark drives) embedded the servo with the data, and hence didn't use separate servo surfaces and didn't require regular head alignment.