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153:) 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
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Cartridges were moved into and out of read stations by two motorized accessor arms, electrically connected via flat cable on a drum. Stage time for data from cartridge to disk was typically 15 seconds, including about two seconds to move the cartridge into a read station, and eight to ten seconds to
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Several models of the 3851 were available. The smallest A1 holding 706 cartridges storing 35.3GB, while the largest A4 held 4,720 cartridges storing 236GB in a 20-foot (6.1 m) long unit. All of the units were also available in the "B models" which added a second controller for on-line backups,
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The Mass
Storage System consisted of a library of cylindrical plastic cartridges, two inches wide and 4 inches (100 mm) long, each holding a spool of tape 770 inches (20 m) long storing 50 MB; each virtual disk required a pair of cartridges. These cartridges were held in a hexagonal
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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
232:, mounted on a rotating drum, then rotated once to read or record a diagonal track. The drive then wound the tape a small step forward and the head rotated to do the next track. Depending on technical definitions this might be even considered a first example of a digital
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while under development, IBM management found a number of niche uses for the concept, and announced it officially as the IBM 3850 on
October 9, 1974. After more than a decade (comparable to the
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as well as offline storage. A second series was released on March 6, 1980, doubling maximum capacity to 472GB. The entire series was discontinued on August 5, 1986.
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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
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The 3851 did not support 3350 staging drives formatted in native mode, only 3350 drives formatted as 3330.
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used to hold large amounts of infrequently accessed data. It was one of the earliest examples of
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308:(Third ed.). IBM. July 1975. GA32-0028-2 – via BitSavers.org.
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The recording method was unusual for its time. The drive pulled the
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disk drives, and physically cached on a combination of 3330 and
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Pugh, Emerson W.; Johnson, Lyle R.; Palmer, John H. (1991).
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from the cartridge and wound it once around a cylindrical
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302:Introduction to the IBM 3850 Mass Storage System
254:fixed and identified by markers along the edge.
165:, 1964–1975), it was withdrawn August 5, 1986.
418:Frankfurt museum's MSS (with video, in German)
205:. These were all connected together with the
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370:IBM Developerworks, Inside System Storage
106:Learn how and when to remove this message
145:Starting in the late-1960s IBM's lab in
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403:IBM details of tape recording method
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366:"Correct use of the term Nearline"
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408:IBM description and announcement
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343:. MIT Press. pp. 536–540.
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438:Computer storage tape media
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238:Exabyte's helical drive
236:recording, long before
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38:Please help
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169:Description
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375:2015-08-16
287:References
66:newspapers
55:"IBM 3850"
324:ignored (
314:cite book
203:destaging
155:hard disk
126:) was an
188:IBM 3330
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