3 ms·

You missed 1983’s 68451 segment/limit MMU for the 68010, as well as 1985’s 68020 with 68851 PMMU. There also were MMU implenentations for 68K without instructio

You missed 1983’s 68451 segment/limit MMU for the 68010, as well as 1985’s 68020 with 68851 PMMU. There also were MMU implenentations for 68K without instruction resumption—Lisa had one, and Apollo initially used two 68000s to support resumption. Finally, there really isn’t much reason to call the Macintosh operating system “DOS-like” or “hidden;” it wasn’t exposed to the user or developer at all except via APIs, and wasn’t some sort of text-based system that had a graphical interface layered on top of it.

Animats 4y ago
That segmented MMU was pretty useless. And, yes, there was the 68020 machine with the separate MMU. You could run a variant of Unix, called A/UX, on it. It was really slow. I've coded for the original MacOS. Yes, it was DOS-like at the OS level. No threads. No processes. No CPU dispatcher. A collection of interrupt driven hacks to allow a little bit of asynchronous processing by registering callbacks. Like you'd do on an Arduino today.
- eschaton 4y ago
  Yes, Apple had the Mac II with support for the 68851, but they weren’t the only ones to use it. Though Sun and HP and Apollo all skipped it and continued using extensions of the paging MMUs they’d developed for the 68010. And plenty of those 68020 systems, whether with custom or Motorola MMUs, were quite fast for their time. Any performance issue with A/UX wss on it and the Mac II hardware design itself. In 1981-4, the era when the original Mac OS was developed, very few systems had threads. And if “has a filesystem and is single-tasking” is your criteria for being “DOS-like” I’m pretty sure every operating system between the inventions of the filesystem and timesharing is also “DOS-like” by your definition. I’d call an operating system “DOS-like” if it used a filesystem with drive letters and short file names with extensions, a command line where argument interpretation is handled by the executed program, text files to script startup and configure device drivers, and the operating system API existed primarily to mediate filesystem and maybe printer and modem access. The original Macintosh operating system had no scripting system, used long volume names and filenames, made file type information inaccessible to the user, didn’t include any sort of command line at all, and made providing ways to interact with documents the main point of its API set—to the point where it had no provisions for anything but graphical applications.
  - pinewurst 4y ago
    I seem to remember the Motorola MMUs requiring significant extra wait states for memory access which was one reason (beyond bugs, lateness, and price) they weren’t popular.
    - Taniwha 4y ago
      There were many MMUs for 68ks at the time - 68000s and 68010s could use the '451, it was very slow and did use wait states, some people put TLB caches around them, Sun and many others built their own MMUs out of SRAM, there was guy who went around the Valley designing Sun-like MMUs for people they were all different, some were broken, the Lisa had a base and bounds MMU (like a PDP-11).. The 68000 couldn't restart page faults - people got around that a lot of ways, some put 2 68ks there and paused one while the other took the fault, mostly though most unixes of the day were swapping ones, the only traps that needed to be restarted were those that extended the stack down, and compilers could be persuaded to generate stack probe code. 68010s fixed that problem and were available around the time we started building paged systems. The 68020s could have an external PMMU (there was another done by Signetics, I think, it was a bit DOA), I think Sun still made their own. The 68030 pulled the PMMU on chip. At the time I worked for Unisoft, the company that did Unix for the Lisa, and A/UX for Apple, it was just one of about 150 Unix ports for other companies we did the bulk of them for 68Ks and most of those for those early 68000/010 - in short they were extremely popular, at the time every man and their dog were trying to make the next great workstation in their garages
      - bitsavers 4y ago
        There's lots of fun Silicon Valley 80's workstation folklore around the MIT 68K PCC port, Unisoft, and Silicon Valley Software's Pascal, Basic and Fortran products. Fun fact that the Sun 1 ran Unisoft Unix before the 68010 'brain transplant' and the BSD port. Also, Unisoft did at least one other UniPlus port for Apple for the YACCintosh. Maybe BigMac as well.
        Taniwha 4y ago

Animats 4y ago

That segmented MMU was pretty useless. And, yes, there was the 68020 machine with the separate MMU. You could run a variant of Unix, called A/UX, on it. It was really slow. I've coded for the original MacOS. Yes, it was DOS-like at the OS level. No threads. No processes. No CPU dispatcher. A collection of interrupt driven hacks to allow a little bit of asynchronous processing by registering callbacks. Like you'd do on an Arduino today.

eschaton 4y ago
Yes, Apple had the Mac II with support for the 68851, but they weren’t the only ones to use it. Though Sun and HP and Apollo all skipped it and continued using extensions of the paging MMUs they’d developed for the 68010. And plenty of those 68020 systems, whether with custom or Motorola MMUs, were quite fast for their time. Any performance issue with A/UX wss on it and the Mac II hardware design itself. In 1981-4, the era when the original Mac OS was developed, very few systems had threads. And if “has a filesystem and is single-tasking” is your criteria for being “DOS-like” I’m pretty sure every operating system between the inventions of the filesystem and timesharing is also “DOS-like” by your definition. I’d call an operating system “DOS-like” if it used a filesystem with drive letters and short file names with extensions, a command line where argument interpretation is handled by the executed program, text files to script startup and configure device drivers, and the operating system API existed primarily to mediate filesystem and maybe printer and modem access. The original Macintosh operating system had no scripting system, used long volume names and filenames, made file type information inaccessible to the user, didn’t include any sort of command line at all, and made providing ways to interact with documents the main point of its API set—to the point where it had no provisions for anything but graphical applications.
- pinewurst 4y ago
  I seem to remember the Motorola MMUs requiring significant extra wait states for memory access which was one reason (beyond bugs, lateness, and price) they weren’t popular.
  - Taniwha 4y ago
    There were many MMUs for 68ks at the time - 68000s and 68010s could use the '451, it was very slow and did use wait states, some people put TLB caches around them, Sun and many others built their own MMUs out of SRAM, there was guy who went around the Valley designing Sun-like MMUs for people they were all different, some were broken, the Lisa had a base and bounds MMU (like a PDP-11).. The 68000 couldn't restart page faults - people got around that a lot of ways, some put 2 68ks there and paused one while the other took the fault, mostly though most unixes of the day were swapping ones, the only traps that needed to be restarted were those that extended the stack down, and compilers could be persuaded to generate stack probe code. 68010s fixed that problem and were available around the time we started building paged systems. The 68020s could have an external PMMU (there was another done by Signetics, I think, it was a bit DOA), I think Sun still made their own. The 68030 pulled the PMMU on chip. At the time I worked for Unisoft, the company that did Unix for the Lisa, and A/UX for Apple, it was just one of about 150 Unix ports for other companies we did the bulk of them for 68Ks and most of those for those early 68000/010 - in short they were extremely popular, at the time every man and their dog were trying to make the next great workstation in their garages
    - bitsavers 4y ago
      There's lots of fun Silicon Valley 80's workstation folklore around the MIT 68K PCC port, Unisoft, and Silicon Valley Software's Pascal, Basic and Fortran products. Fun fact that the Sun 1 ran Unisoft Unix before the 68010 'brain transplant' and the BSD port. Also, Unisoft did at least one other UniPlus port for Apple for the YACCintosh. Maybe BigMac as well.
      - Taniwha 4y ago