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Concept
DECtape
Résumé
DECtape, originally called Microtape, is a magnetic tape data storage medium used with many Digital Equipment Corporation computers, including the PDP-6, PDP-8, LINC-8, PDP-9, 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 are wide, and formatted into blocks of data that can each be read or written individually. Each tape stores 184K 12-bit PDP-8 words or 144K 18-bit words. Block size is 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, because the system is block-oriented and allows random seeking, DECtape behaves like a very slow disk drive.
DECtape has 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 are simple LINC instructions for reading and writing tape blocks using a single machine instruction. 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 uses a physically incompatible tape format (1⁄2-inch tape on 10-inch reels, where LINC tape and DECtape used 3⁄4-inch tape on 4-inch reels).
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.
Source officielle
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