PDP-10
was a computer manufactured by Digital_Equipment_Corporation (DEC) from the late 1960s on; the name stands for "Programmed Data Processor model 10". It was the machine that made time-sharing common; it looms large in hacker folklore because of its adoption in the mid-1970s by many university computing facilities and research labs, including MIT's AI Lab and Project_MAC, Stanford's SAIL, and CMU. The PDP-10 architecture was an improved version of the earlier PDP-6 architecture, sharing the same 36-bit word length and slightly extending the instruction set. Some aspects of the instruction_set are still considered unsurpassed, most notably the "byte" instructions which operated on arbitrary sized bit-fields (at that time a byte was not necessarily eight bits). The original PDP-10 processor was the KA10, introduced in 1968. It used discrete transistors packaged in DEC's Flip_Chip® technology. In 1973, the KA10 was replaced by the KI10, which used TTL ICs. This in turn was replaced in 1975 by the KL10, which was built from ECL, microprogrammed, and had cache memory. A smaller, less expensive model, the KS10, was introduced in 1978, using TTL and Am2901 bit-slice components. The KA10 had a maximum main memory capacity of 256 Kwords (equivalent to 1152 Kbytes). Memory management consisted of two sets of protection and relocation registers. This allowed each half of a user process address_space to be limited to a specified section of main_memory designated by the base physical address and size. The high segment was normally read-only, and used for shareable code, while the low segment was used for writeable data. The KI10 and later processors offered paged memory management, supporting a physical address space of 4 Mwords. The "Model B" KL10 removed the 256 Kword limitation on the process address space, as well, by allowing the use of up to 32 "sections" of up to 256 Kwords each. The original PDP-10 operating system was simply called "Monitor", but was later renamed to TOPS-10, at which time the system became known as the DECsystem-10. Early versions of Monitor and TOPS-10 formed the basis of Stanford's WAITS operating system and the Compuserve time-sharing system, while MIT developed their own ITS (named in parody of the CTSS for the IBM 7094). BBN developed add-on paging hardware for the KA10 which was used by their Tenex operating system. DEC later ported Tenex to the KL10, enhanced it considerably, and named it TOPS-20, forming the basis of the DECSYSTEM-20 line. The PDP-10 was eventually eclipsed by the VAX supermini machines (descendants of the PDP-11) when DEC recognized that the PDP-10 and VAX product lines were competing with each other and decided to concentrate its software development effort on the more profitable VAX. The PDP-10 product line cancellation was announced in 1983, following the failure of the Jupiter Project at DEC to build a new high-end processor. This event spelled the doom of ITS and the technical cultures that had spawned the original jargon_file, but by the 1990s it had become something of a badge of honorable old-timerhood among hackers to have cut one's teeth on a PDP-10. Third-party attempts to sell PDP-10 clones were relatively unsuccessful; see Foonly and Mars. Researchers at Xerox_PARC, frustrated by management's refusal to let them purchase a PDP-10, designed and constructed two clone systems named "MAXC" (pronounced "max") for their own use. The PDP-10 assembly_language instructions LDB and DPB (load/deposit byte) live on as functions in the programming_language Common_Lisp. Will_Crowther created Adventure, the prototypical computer role-playing game, for a PDP-10. Walter_Bright originally created Empire for the PDP-10. Some of the CGI for the Disney science fiction movie ''TRON'' was rendered on the Foonly F-1 PDP-10 clone; it is also noteworthy that the PDP-10 has a TRON instruction (Test Right-halfword Ones and skip if Not masked) with the Opcode 666... ---- This article is based in part on one in the jargon_file; the jargon_file is in the public domain. ''See also'': TOPS-10, ITS, WAITS.Further Reading
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