 | |
 An incomplete PDP-15 | |
| Developer | Digital Equipment Corporation |
|---|---|
| Product family | Programmed Data Processor |
| Type | Minicomputer |
| Released | February 1970; 56 years ago (1970-02) |
| Lifespan | 9 years |
| Introductory price | 15,600 |
| Discontinued | 1979 |
| Units sold | 790[1] |
| Operating system | DECsys, RSX-15,XVM/RSX,MUMPS, DOS-15[2] |
| Platform | PDP 18-bit |
| Predecessor | PDP-9 |
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ThePDP-15 was an18-bitminicomputer byDigital Equipment Corporation that first shipped in February 1970.[3] It was the fifth and last of DEC's 18-bit machines, a series that had started in December 1959 with thePDP-1.[4]: P.4 More than 400 were ordered within the first eight months.[4]: p.16 A later model, the PDP-15/76, was bundled with a completePDP-11, allowing the PDP-15 to use peripherals for the PDP-11's popularUnibus 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 earlierPDP-9 that was constructed usingsmall-scale integrationintegrated circuits, which made it smaller and less expensive than the PDP-9'sflip chips which used individualtransistors. A basic 8 kW PDP-9 cost about $35,000 in 1968 (equivalent to $324,000 in 2025), whereas the PDP-15 with 4 kW was only $15,600 (equivalent to $129,000 in 2025) and a fully-equipped system with 8 kW,punch tape,KSR-35 terminal,math coprocessor and dualDECtape was $36,000 (equivalent to $298,000 in 2025), making a complete system significantly less expensive than the earlier machine.[5]
In addition tooperating systems, the PDP-15 has compilers forFortran[6] andALGOL.[7]
The 18-bit PDP systems preceding the PDP-15 were named PDP-1,PDP-4,PDP-7 andPDP-9. The last PDP-15 was produced in 1979.[8]
The PDP-15 was DEC's only 18-bit machine constructed fromTTLintegrated circuits rather than discrete transistors, and, like every DEC 18-bit system could be equipped with:
The PDP-15 models offered by DEC were:[11][12][10][9][13]
DECsys,RSX-15, andXVM/RSX were theoperating systems supplied by DEC for the PDP-15. Abatch processingmonitor (BOSS-15: Batch Operating Software System) was also available.[7]
The first DEC-supplied mass-storageoperating 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 storagefor personal programs and data. A second DECtape was used as a scratch tape by the assembler and theFortran compiler.[16]
RSX-15 was released by DEC in 1971.[17] The main architect for RSX-15 (later renamed XVM/RSX) was Dennis "Dan" Brevik.[18][19]
OnceXVM/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."[20]
TheRSX-11 operating system began as a port of RSX-15 to thePDP-11, although it later diverged significantly in terms of design and functionality.[21]
Commenting on theRSX acronym, Brevik says:[22]
"At first I called the new system DEX-15. It was an acronym for 'Digital's Executive - for the PDP-15.' The homonymic relation between DEC, DEX and deques (used as the primary linkage mechanism in the kernel) appealed to my sense of whimsy. People readily adopted the acronym without question.
But in a short time I was asked to submit the choice to the corporate legal department for a trademark search and registration. They sent me a memo that DEX was already trademarked by some paper company and I would have to rename the product. I pointed out to them that software and paper mills didn't seem to have a hell of a lot of connection, but they wouldn't budge.
So I sat down with pencil and paper, and in a few moments came up with better than a dozen candidate acronyms and names. My purpose was to come up with a good acronym and then find some appropriate words to justify it. For example, X always appealed to me as part of an acronym because it is pronounced so forcefully, inferring (at least to me) some power and drama. I used a lot of X's. These potential acronyms were submitted back to the legal department. At the time I had no favorite.
In a week or so they came back with a subset of my list that they could accept as trademarks. It was left to me to make the final choice.
Bob Decker and I met in my office one afternoon to discuss the choice. Bob was a marketeer who worked for me. I chalked all the candidates on the blackboard and we started going through them one by one, pronouncing each out loud, savoring the sound, trying to get the feel of each one. After ten minutes or so we had narrowed down the selection to three.
Bob sat back in silence as I kept looking at each acronym, seeing how it flowed off my tongue, what impression it gave me, and most importantly, the overall feeling about it. After three or four minutes a strong feeling came over me about one of them. It really felt right. I looked at Bob and announced, "It's RSX". I went to the board and erased all the rest until the only writing left was RSX. It even looked right.
I have absolutely no memory about the other candidate acronyms. They are lost forever, I suppose. Well, maybe there's just a chance that the legal department kept copies of the correspondence - after all they are lawyers and they seem to hold on to everything (especially my money).
Oh, by the way, the acronym stood for 'Real-Time System Executive.' Years later that was changed to 'Resource Sharing Executive,' which I think is even better.
...And that is how RSX got its name, on the 3rd floor of building 5 in the old mill."
Later versions of the PDP-15 could run a real-time multi-user OS calledXVM/RSX, an outgrowth of RSX-15.[10][7] TheXVM upgrade to RSX was multi-user, and enabled up to six concurrent teletype-based users.[23] XVM Support for the PDP-15/76 included using anRK05 disk drive.[20]
TheMUMPS operating system, which was originally developed in 1966,[8] was developed on the PDP-7 outside DEC. It is also available for the PDP-15.
DEC provided mathematical, scientific and commercial software application tools.[10]: pp.10/13-10/15 [24]
by 1977, 790 machines had been shipped - more than the total of all other DEC 18-bit machines.
to be taken out of operation at the end of 1982.
