4 ms·

> Standardization on 8-bit multiples only really occurred with the IBM 360 in the late 1960s. It's not "standardization" when only one model from one company i

> Standardization on 8-bit multiples only really occurred with the IBM 360 in the late 1960s. It's not "standardization" when only one model from one company is doing it. The 8-bit byte was common in microcomputers and as they grew to dominate people's programming, you could claim it became some kind of de facto standard in the 70s or 80s. The de facto standard was documented by a standards body in the 90s. FWIW, in a CS program in the 90s, I was taught that 8-bit was most common, but not "standard." https://en.wikipedia.org/wiki/Byte#cite_note-ISO_IEC_2382-1_1993-9 https://en.wikipedia.org/wiki/Byte#cite_note-ISO_IEC_2382-1_... Word length was even less common across architectures, but again, we ended up setting current definitions based on microcomputer use.

TheOtherHobbes 3y ago
Micros were 8 bits because that's the sweet spot in the trade off between usefulness, complexity, and expense. With 8 bits you have a reasonable instruction space, simple access to a 16-bit address space, and a good platform for ASCII. It's a minimal viable CPU - powerful enough to get non-trivial general purpose work done, easy to package into VLSI, and cheap enough to sell in quantity. But the design went in the opposite direction. The original micro - in terms of market positioning - was the PDP-8, and that was 12-bits. The 16-bit PDP-11s were a step up from the 8, and the 8080 etc were a step back down.
- couchand 3y ago
  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..
  - 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.
timbit42 3y ago
> It's not "standardization" when only one model from one company is doing it. It is when that company is IBM and the model is their new platform that all of their future systems will be based on. They were a juggernaut back in those days, more than Microsoft is today.

TheOtherHobbes 3y ago

Micros were 8 bits because that's the sweet spot in the trade off between usefulness, complexity, and expense. With 8 bits you have a reasonable instruction space, simple access to a 16-bit address space, and a good platform for ASCII. It's a minimal viable CPU - powerful enough to get non-trivial general purpose work done, easy to package into VLSI, and cheap enough to sell in quantity. But the design went in the opposite direction. The original micro - in terms of market positioning - was the PDP-8, and that was 12-bits. The 16-bit PDP-11s were a step up from the 8, and the 8080 etc were a step back down.

couchand 3y ago
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..
- 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.

timbit42 3y ago

> It's not "standardization" when only one model from one company is doing it. It is when that company is IBM and the model is their new platform that all of their future systems will be based on. They were a juggernaut back in those days, more than Microsoft is today.