3 ms·

Can you help me out with your last paragraph? My understanding was that the PDP-8 was squarely a mini, not a micro.

timbit42 3y ago
The DEC PDP-8 is a mini computer but because it was so small and inexpensive, it was often used as a personal computer. Micro computers were also personal computers, especially in the beginning, so perhaps there is some conflation there.
- PaulHoule 3y ago
  It was a much smaller machine than the PDP-11 and the PDP-10. In 1981 Manchester Memorial High School had a PDP-8 which had two floppy drives, a large printing terminal, and two unusual video terminals that were a bit smarter than the common VT-100 connected via "current loop" that had two 8-inch floppy drives for storage. That machine could be brought up in single user or multitasking modes: it could support 1, 2 or 3 people programming BASIC or run larger applications like https://en.wikipedia.org/wiki/Colossal_Cave_Adventure https://en.wikipedia.org/wiki/Colossal_Cave_Adventure in single-user mode on the printing terminal. A bigger school, like one in Milford, NH, had a PDP-11 with about 20 terminals and an OS called RSTS/E that was mainly used to let people log in and use BASIC the way they would on a Commodore PET or TRS-80 except it was timesharing, it had tape storage and some kind of primitive hard drive. By the late 1980s Manchester Memorial got a VAX-11 which was similar to the 386 in architecture and ran an OS very much like Linux. They would teach you to program in PASCAL using the compiler on the command line, there were maybe 8 terminals in the classroom and then another 8 or so terminals in other parts of the school to run administrative applications. DEC never found its footing in a microprocessor world. It is not difficult to make a PDP-8 on FPGA https://hackaday.io/project/179357-pdp-8-fpga https://hackaday.io/project/179357-pdp-8-fpga and Digital had made single chip "microprocessor" versions of the PDP-11 and the VAX-11. DEC could have made a machine based on a single-chip PDP-11 that would have competed with the IBM Personal Computer in some ways but would have faced the problem that user space memory addresses were 16-bit. For a "personal" computer you want to run 1 big BASIC and not 10 little BASICs. The IBM PC had a terribly hackish way to access a 640k user space but developers thought it was worth the hassle. Similarly, other vendors like Motorola and Intel and National Semi were trying to develop a model for "32-bit" machines similar to the VAX, one can imagine that Digital might have aggressively transitioned the VAX line to "microcomputers". A VAX workstation would have trounced an IBM PC AT. Maybe Apple would have switched to VAX when Motorola came apart and Intel might be remembered as a RAM manufacturer.
  - jhallenworld 3y ago
    Bitsavers has a bunch of competitive analysis documents from 1980s DEC that are interesting to read: http://www.bitsavers.org/pdf/dec/competitiveAnalysis/ http://www.bitsavers.org/pdf/dec/competitiveAnalysis/ You can feel the desperation..
- jhallenworld 3y ago
  OS/8 was a single user OS (like RT11), so it often was used as a personal computer. It inspired CP/M. 6-bit chars were popular on this machine since you could fit two in one word, and uppercase only a thing. Strings in BASIC used 6-bit chars, but you could PRINT all ASCII (especially control characters) with a special PNT() function (only usable as a PRINT argument). If you look at the available OS/8 images, you'll find "business BASIC"- at least one change compared to regular OS/8 basic was support for 8-bit strings. Floppies used 8-bit bytes. You wasted 4-bits out of every two for image files.
  - rahen 3y ago
    To be very pedantic, CP/M was mostly inspired by TOPS-10, which also inspired OS/8, RT/11, and even PC-DOS.
    - timbit42 3y ago
      Hmm. My notes suggest TOPS-10 inspired Data General's RDOS, which inspired CP/M.
NikkiA 3y ago
Here's a small 'micro' PDP-8: https://en.wikipedia.org/wiki/DECmate#/media/File:VT78.jpg https://en.wikipedia.org/wiki/DECmate#/media/File:VT78.jpg Also, the VT78's precursor was the PDP8/f which was little bigger than an altair, definitely in the microcomputer camp.

The DEC PDP-8 is a mini computer but because it was so small and inexpensive, it was often used as a personal computer. Micro computers were also personal computers, especially in the beginning, so perhaps there is some conflation there.

PaulHoule 3y ago
It was a much smaller machine than the PDP-11 and the PDP-10. In 1981 Manchester Memorial High School had a PDP-8 which had two floppy drives, a large printing terminal, and two unusual video terminals that were a bit smarter than the common VT-100 connected via "current loop" that had two 8-inch floppy drives for storage. That machine could be brought up in single user or multitasking modes: it could support 1, 2 or 3 people programming BASIC or run larger applications like https://en.wikipedia.org/wiki/Colossal_Cave_Adventure https://en.wikipedia.org/wiki/Colossal_Cave_Adventure in single-user mode on the printing terminal. A bigger school, like one in Milford, NH, had a PDP-11 with about 20 terminals and an OS called RSTS/E that was mainly used to let people log in and use BASIC the way they would on a Commodore PET or TRS-80 except it was timesharing, it had tape storage and some kind of primitive hard drive. By the late 1980s Manchester Memorial got a VAX-11 which was similar to the 386 in architecture and ran an OS very much like Linux. They would teach you to program in PASCAL using the compiler on the command line, there were maybe 8 terminals in the classroom and then another 8 or so terminals in other parts of the school to run administrative applications. DEC never found its footing in a microprocessor world. It is not difficult to make a PDP-8 on FPGA https://hackaday.io/project/179357-pdp-8-fpga https://hackaday.io/project/179357-pdp-8-fpga and Digital had made single chip "microprocessor" versions of the PDP-11 and the VAX-11. DEC could have made a machine based on a single-chip PDP-11 that would have competed with the IBM Personal Computer in some ways but would have faced the problem that user space memory addresses were 16-bit. For a "personal" computer you want to run 1 big BASIC and not 10 little BASICs. The IBM PC had a terribly hackish way to access a 640k user space but developers thought it was worth the hassle. Similarly, other vendors like Motorola and Intel and National Semi were trying to develop a model for "32-bit" machines similar to the VAX, one can imagine that Digital might have aggressively transitioned the VAX line to "microcomputers". A VAX workstation would have trounced an IBM PC AT. Maybe Apple would have switched to VAX when Motorola came apart and Intel might be remembered as a RAM manufacturer.
- jhallenworld 3y ago
  Bitsavers has a bunch of competitive analysis documents from 1980s DEC that are interesting to read: http://www.bitsavers.org/pdf/dec/competitiveAnalysis/ http://www.bitsavers.org/pdf/dec/competitiveAnalysis/ You can feel the desperation..
jhallenworld 3y ago
OS/8 was a single user OS (like RT11), so it often was used as a personal computer. It inspired CP/M. 6-bit chars were popular on this machine since you could fit two in one word, and uppercase only a thing. Strings in BASIC used 6-bit chars, but you could PRINT all ASCII (especially control characters) with a special PNT() function (only usable as a PRINT argument). If you look at the available OS/8 images, you'll find "business BASIC"- at least one change compared to regular OS/8 basic was support for 8-bit strings. Floppies used 8-bit bytes. You wasted 4-bits out of every two for image files.
- rahen 3y ago
  To be very pedantic, CP/M was mostly inspired by TOPS-10, which also inspired OS/8, RT/11, and even PC-DOS.
  - timbit42 3y ago
    Hmm. My notes suggest TOPS-10 inspired Data General's RDOS, which inspired CP/M.

NikkiA 3y ago

Here's a small 'micro' PDP-8: https://en.wikipedia.org/wiki/DECmate#/media/File:VT78.jpg https://en.wikipedia.org/wiki/DECmate#/media/File:VT78.jpg Also, the VT78's precursor was the PDP8/f which was little bigger than an altair, definitely in the microcomputer camp.