IBM 3850
Encyclopedia
The IBM 3850 Mass Storage System was an online
tape library
used to hold large amounts of infrequently accessed data.
began development of a low-cost mass storage system based on magnetic tape cartridges. The tapes would be accessed automatically by a robot (known as an accessor) and fed into a reader/writer unit that could work on several tapes at the same time. Originally the system was going to be used as a directly attached memory device, but as the speed of computers grew in relation to the storage, the product was re-purposed as an automated system that would offload little-used data from hard disk
systems. Known internally as Comanche while under development, IBM management found a number of niche uses for the concept, and announced it officially as the IBM 3850 on October 9th, 1974.
The recording method was unusual for its time. The tape
was wound around a cylindrical mandrel
in a helix
and stopped. The drive head
rotated once (on a rotating drum) to record a diagonal track. Then tape was wound a small step, so the head could iterate over next diagonal track. Depending on technical definitions this might be even considered a first example of a digital helical scan
recording, long before Exabyte's helical drive (although analog
video
helical recording systems
were developed earlier).
When free disk space was required a group of cylinders were selected to be destaged to tape, these were transferred with minimal or no change of format. Each tape could store 202 cylinder images of 19 tracks each, half of the 404 cylinders in a 3330 disk pack. Cylinder locations on the tape were fixed and identified by markers along the edge.
ONLINE
ONLINE is a magazine for information systems first published in 1977. The publisher Online, Inc. was founded the year before. In May 2002, Information Today, Inc. acquired the assets of Online Inc....
tape library
Tape library
In computer storage, a tape library, sometimes called a tape silo, tape robot or tape jukebox, is a storage device which contains one or more tape drives, a number of slots to hold tape cartridges, a barcode reader to identify tape cartridges and an automated method for loading tapes...
used to hold large amounts of infrequently accessed data.
History
Starting in the late-1960s IBM's lab in Boulder, ColoradoBoulder, Colorado
Boulder is the county seat and most populous city of Boulder County and the 11th most populous city in the U.S. state of Colorado. Boulder is located at the base of the foothills of the Rocky Mountains at an elevation of...
began development of a low-cost mass storage system based on magnetic tape cartridges. The tapes would be accessed automatically by a robot (known as an accessor) and fed into a reader/writer unit that could work on several tapes at the same time. Originally the system was going to be used as a directly attached memory device, but as the speed of computers grew in relation to the storage, the product was re-purposed as an automated system that would offload little-used data from hard disk
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...
systems. Known internally as Comanche while under development, IBM management found a number of niche uses for the concept, and announced it officially as the IBM 3850 on October 9th, 1974.
Description
The MSS (as it was known) consisted of a library of cylindrical plastic cartridges, two inches wide and 4 inches (101.6 mm) long, each holding a spool of tape 770 inches (19.6 m) long storing 50MB. These cartridges were held in a hexagonal array of bins in the IBM 3851 Mass Storage Facility. New cartridges were rolled into the facility and were automatically stored in a vacant bin. The data was accessed via one or two IBM 3330 disk drives, the data being transferred automatically between cartridge and disk drive in processes called staging and destaging. These were all connected together with the IBM 3830 Storage Control (also used for disk storage alone), the entire system making up a 3850 unit.The recording method was unusual for its time. The tape
Magnetic tape data storage
Magnetic tape data storage uses digital recording on to magnetic tape to store digital information. Modern magnetic tape is most commonly packaged in cartridges and cassettes. The device that performs actual writing or reading of data is a tape drive...
was wound around a cylindrical mandrel
Mandrel
A mandrel is one of the following:* an object used to shape machined work.* a tool component that grips or clamps materials to be machined.* a tool component that can be used to grip other moving tool components.- Variants :...
in a helix
Helix
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...
and stopped. The drive head
Tape head
A tape head is a type of transducer used in tape recorders to convert electrical signals to magnetic fluctuations and vice versa.-Principles of operation:...
rotated once (on a rotating drum) to record a diagonal track. Then tape was wound a small step, so the head could iterate over next diagonal track. Depending on technical definitions this might be even considered a first example of a digital helical scan
Helical scan
Helical scan is a method of recording high bandwidth signals onto magnetic tape. It is used in reel-to-reel video tape recorders, video cassette recorders, digital audio tape recorders, and some computer tape drives....
recording, long before Exabyte's helical drive (although analog
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
helical recording systems
U-matic
U-matic is an analog recording videocassette format first shown by Sony in prototype in October 1969, and introduced to the market in September 1971. It was among the first video formats to contain the videotape inside a cassette, as opposed to the various Reel-to-Reel or open-reel formats of the...
were developed earlier).
When free disk space was required a group of cylinders were selected to be destaged to tape, these were transferred with minimal or no change of format. Each tape could store 202 cylinder images of 19 tracks each, half of the 404 cylinders in a 3330 disk pack. Cylinder locations on the tape were fixed and identified by markers along the edge.