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DECtape (originally called ''Microtape'') was a magnetic tape data storage medium used with many Digital Equipment Corporation computers, including the PDP-6, PDP-8, LINC-8, PDP-10, PDP-11, PDP-12, and the PDP-15. On DEC's 32-bit systems, VAX/VMS support for it was implemented but did not become an official part of the product lineup. DECtapes were 3/4 inch wide, and formatted into blocks of data that could each be read or written individually. Each tape stored 184K 12-bit PDP-8 words or 144K 18-bit words. Block size was 128 12-bit words (for the 12-bit machines), or 256 18-bit words for the other machines (16, 18, 32, or 36 bit systems). From a programming point of view, DECtape behaved like a very slow disk drive. ==Origins== DECtape had its origin in the LINCtape tape system, which was originally designed by Wesley Clark at the MIT Lincoln Laboratory as an integral part of the LINC computer. There were simple LINC instructions for reading and writing tape blocks using a single machine instruction.〔Mary Allen Wilkes and Wesley A. Clark, 18: Magnetic Tape Instructions, (Programming the LINC ), LINC Volume 16, Section 2, June, 1965; pages 80-104.〕 The design of the LINC, including LINCtape, was placed in the public domain because its development had been funded by the government. LINCtape drives were manufactured by several companies, including Digital. In turn, LINCtape's origin can be found in the magnetic tape system for the historic Lincoln Laboratory TX-2 computer, designed by Richard L. Best and T. C. Stockebrand. The TX-2 Tape System is the direct ancestor of LINCtape, including the use of two redundant sets of five tracks and a direct drive tape transport, but it used a physically incompatible tape format (½-inch Tape on 10-inch reels, where LINC tape and DECtape used ¾-inch tape on 4-inch reels).〔R. L. Best and T. C. Stockerbrand, A Computer-Integrated Rapid Access Magnetic Tape System with Fixed Address, (Proceedings of the Western Joint Computer Conference: Contrasts in Computers ), May 6–8, 1958; pages 42-46.〕〔Herb Johnson, (Tape reels and hubs - "fit" ) section of (LINC, LINCtape, DECtape ), Nov. 26, 2013.〕 Digital initially introduced the Type 550 Microtape Control and Type 555 Dual Microtape Transport as peripherals for the PDP-1 and PDP-4 computers, both 18-bit machines. DEC advertised the availability of these peripherals in March and May, 1963, and by November, planning was already underway to offer the product for the 12-bit PDP-5 and 36-bit PDP-6, even though this involved a change in recording format.〔Levin H. Campbell, (Court ruling ), Digital Equipment Corporation, Plaintiff, Appellant, v. Sidney A. Diamond, Etc., et al., 653 F.2d 701 (1st Cir. 1981), June 12, 1981; see paragraph 5 for the chronology of introduction.〕〔Leonard M. Hantman, Microtape: Its Features and Applications, (Second Annual Meeting of the Digital Equipment Corporation User's Society (DECUS) ), Lawrence Radiation Laboratories, Livermore, Nov. 18-19, 1963; see the ''Future Trends'' section, page 15.〕 The initial specifications for the Type 550 controller discussed a significant advance beyond the LINCtape, the ability to read and write in either direction.〔(555/550 Micro-Tape Dual Transport & Tape Control ), Digital Equipment Corporation, May, 1963.〕 By late 1964, the Type 555 transport was being marketed as a DECtape transport.〔(555 DECtape Dual Transport ), Digital Equipment Corporation, H-555, Dec. 1964; The start of Chapter 1 contains the term 'DECtape'.〕 The tape transport used on the LINC was essentially the same as the Type 555 transport, with the same interface signals and the same physical tape medium. The LINC and DEC controllers, however, were incompatible, and the positions of the supply and take-up reels were reversed between the LINC and DEC tape formats. While LINCtape supported high-speed bidirectional block search, it only supported actual data read and write operations in the forward direction. DECtape used a significantly different mark track format to provide for the possibility of read and write operations in either direction, although not all DECtape controllers supported reverse read. DEC applied for a patent on the enhanced features incorporated into DECtape in late 1964.〔Thomas C. Stockebrand, Bidirectional Retrieval of Magnetically Recorded Data, , issued June 4, 1968.〕 It is notable that the inventor listed on this patent, Thomas Stockebrand, was also an author of the paper on the TX-2 tape system from which the LINC tape was derived.〔 Eventually, the TC12-F tape controller on the PDP-12 supported both LINCtape and DECtape on the same transport. As with the earlier LINC-8, the PDP-12 was a PDP-8 augmented with hardware support for the LINC instruction set and associated laboratory peripherals. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「DECtape」の詳細全文を読む スポンサード リンク
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