Unlike most new threads that end up in ancient history and then have to be killed, this one starts out with ancient history! What an opportunity for us Jurassic-types. Since I was non-email-capable for two weeks, I read all old posts before adding my 2 cents' worth, which embody responses to many previous posts. Don't know about MFT, but MVT was reclassified as Class C (meaning frozen, no more new releases, no more fixes) in November, 1977. I continued working with it and other OS/360 variants off and on until late 1983. PCP did indeed stand for Primary Control Program. I used BPS, TOS, and DOS from mid-1966 to late 1971. The worst thing that the tape-resident-SYSRES TOS had to do was to recover from an I/O error on the SYSRES tape itself - backspace or forwardspace to fetch the system module to do the recovery, whose logic said to retry the failing I/O, so move the tape back to where the error was, re-read ten times, then, if it still failed, move the tape way back to the beginning again to locate the system module to do the ABEND process. Truly heinous and egregious. BPS had a 2-pass 8K card assembler available for hard-core warriors. You put the standard BPS self-loading IPL deck (all of 6 cards) in the card reader followed by the 8K card assembler phase 1 object deck followed by your source deck and IPLed from the card reader. The first phase punched one output card, containing intermediate Assembly data, for each input source card. Then you put the 6-card BPS IPL deck in the card reader followed by the 8K card assembler phase 2 object deck followed by all the cards punched out in phase 1 and IPLed from the card reader again. This second phase punched the final object deck. In order to run the program thus assembled, you again put the 6-card self-loading IPL deck in the card reader followed by this object deck and reIPLed from the card reader. So you had an "operating system" with major limitations: (1) only one program could run at a time, (2) you had to re-IPL whenever you wanted to run a different program, and (3) the operator performed the operating system's functions of running one job after another. The first version of BPS did not support multiplexing on the multiplexor channel. Regardless of how cleverly you tried to overlap I/O, when you did the EXCP the supervisor would do a SIO to start the I/O and then a TIO loop until the I/O completed before returning control to the instruction just after the EXCP's SVC. More heinosity and egregiousness. MVT was first virtualized in early 1974 as OS/VS2 Release 1, better known as SVS (Single Virtual Storage). A fuller version, OS/VS2 Release 2, was available a year or so later, and it was quickly renamed MVS for Multiple Virtual Storages. MFT evolved into VS1. I heard about COS, for Compatibility Operating System, but I'm not sure what was made compatible with what (maybe it was a 360/20 emulator running on a 360/30?). Bill Fairchild Plainfield, IL
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