PDP-15

The PDP-15 was an 18-bit minicomputer by Digital Equipment Corporation that first shipped in February 1970. It was the fifth and last of DEC's 18-bit machines, a series that had started in December 1959 with the PDP-1. More than 400 were ordered within the first eight months. A later model, the PDP-15/76, was bundled with a complete PDP-11, allowing the PDP-15 to use peripherals for the PDP-11's popular Unibus system. The last PDP-15 was produced in 1979, with total sales of about 790 units.

The PDP-15 was essentially a version of the earlier PDP-9 that was constructed using small-scale integration integrated circuits, which made it smaller and less expensive than the PDP-9's flip chips which used individual transistors. A basic 8 kW PDP-9 cost about $35,000 in 1968 (), whereas the PDP-15 with 4 kW was only $15,600 () and a fully-equipped system with 8 kW, punch tape, KSR-35 terminal, math coprocessor and dual DECtape was $36,000 (), making a complete system significantly less expensive than the earlier machine.

In addition to operating systems, the PDP-15 has compilers for Fortran and ALGOL.

History The 18-bit PDP systems preceding the PDP-15 were named PDP-1, PDP-4, PDP-7 and PDP-9. The last PDP-15 was produced in 1979.

Hardware

The PDP-15 was DEC's only 18-bit machine constructed from TTL integrated circuits rather than discrete transistors, and, like every DEC 18-bit system could be equipped with: an optional X-Y (point-plot or vector graphics) display. a hardware floating-point option, with a 10x speedup. up to 128K words of core main memory

Models The PDP-15 models offered by DEC were: PDP-15/10: a 4K-word paper-tape-based system PDP-15/20: 8K, added DECtape PDP-15/30: 16K word, added memory protection and a foreground/background monitor PDP-15/35: Added a 524K-word fixed-head disk drive PDP-15/40: 24K memory PDP-15/50:A PDP-15/50, described then as "expensive to maintain," was still running in 1982.

PDP-15/76 PDP-15/76: 15/40 plus PDP-11 frontend. The PDP-15/76 was a dual-processor system that shared memory with an attached PDP-11/05. The PDP-11 served as a peripheral processor and enabled use of Unibus peripherals.

Software DECsys, RSX-15, and XVM/RSX were the operating systems supplied by DEC for the PDP-15. A batch processing monitor (BOSS-15: Batch Operating Software System) was also available.

DECsys The first DEC-supplied mass-storage operating system available for the PDP-15 was DECsys, an interactive single-user system. This software was provided on a DECtape reel, of which copies were made for each user. This copied DECtape was then added to by the user, and thus was storage for personal programs and data. A second DECtape was used as a scratch tape by the assembler and the Fortran compiler.

RSX-15 RSX-15 was released by DEC in 1971. The main architect for RSX-15 (later renamed XVM/RSX) was Dennis "Dan" Brevik.

Once XVM/RSX was released, DEC facilitated that "a PDP-15 can be field-upgraded to XVM" but it required "the addition of the XM15 memory processor."

The RSX-11 operating system began as a port of RSX-15 to the PDP-11, although it later diverged significantly in terms of design and functionality.

Origin of the RSX-15 name Commenting on the RSX acronym, Brevik says:

XVM/RSX Later versions of the PDP-15 could run a real-time multi-user OS called XVM/RSX, an outgrowth of RSX-15. The XVM upgrade to RSX was multi-user, and enabled up to six concurrent teletype-based users. XVM Support for the PDP-15/76 included using an RK05 disk drive.

non-DEC The MUMPS operating system, which was originally developed in 1966, was developed on the PDP-7 outside DEC. It is also available for the PDP-15.

Application software DEC provided mathematical, scientific and commercial software application tools. "Commercial Subroutine Package (CSP) ... compatible with the IBM 1130 commercial subroutine package."

PDP-15

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