6 ms·

According to history, there were three microprocessors in the running for the IBM PC. They were the Intel 8088, the Motorola 68000, and the Texas Instruments TM

According to history, there were three microprocessors in the running for the IBM PC. They were the Intel 8088, the Motorola 68000, and the Texas Instruments TMS99000. If I remember correctly, the Intel had lots of 8088s available immediately (so IBM could do things like lifecycle testing), and Motorola did not have enough 68000s available yet. IBM was concerned about how much memory you would be able to use with future iterations of the 99000. The 68000 series did see use in the Macintosh, Amiga, Sharp X68000, and it completely dominated the Unix workstation space in the late 1980s. There were a lot of companies who thought, “I’ll buy a Unix license, buy some M68000s, and sell workstations.” Most of these companies disappeared. Later Unix workstations used all sorts of architectures.

pbj1968 3y ago
Also saw use in soda machines… SEGA genesis…
- sprash 3y ago
  And Palm devices.
- guenthert 3y ago
  In the mid to late eighties, the MC68K was also often used in high end (small series) test&measurement equipment, e.g. HP3458A and Datron 1271/1281 DMM, HP166x{A,B,C} logic analyzers ...
cesaref 3y ago
Right, the 68k was the most logical step up from the early 8 bit processors in typical home computers (except for the TI99/4a which went in another direction). They were easy to design for, and easy to program (68k assembler is pretty elegant). The 68008 as mentioned was used in the Sinclair XL, with the 32 bit bus versions in the ST/Amiga/Mac. Initially limited to a 24 bit address bus, but when a machine was topping out at 1Mb, 16Mb seemed a long way away! I think the MMU was introduced with the 68020, which then appeared in early Sun 3s, and HP9000s, prior to the RISC invasion. Those machines seemed super fast at the time.
- cmrdporcupine 3y ago
  As an Atari ST user, I was a big fan of the 68k back in the 80s but even I'd have to admit that the 808x architecture made the most sense for IBM to take given that it offered continuity with the CP/M S100-bus 8080/z80 machines that were fairly dominant in the nascent "business computing" market at that point. Forking CP/M (cuz let's admit that's basically what PC-DOS was) and offering something similar-but-different to those systems was low-risk. And their original intent in fact was to in fact sell a full-on CP/M machine. FWIW the Atari ST is what you get when you take a CP/M/PC-DOS-style OS and bolt it onto the 68k. Syscalls were basically 1:1 with MS-DOS, and even used an MS-DOS compatible filesystem. But big-endian. If you want to see what an IBM PC built around the 68k would have looked like, that's not far off.
  - jdswain 3y ago
    So maybe being a bit pedantic here, but the Atari ST was originally going to use CP/M 68k, but part way through development they changed the base OS from that to what was more of a MS-DOS clone (which as others have said was also mainly a CP/M 80 clone). I think this was done to have better compatibility with the GEM layer, so the Atari ST OS, TOS, was more like MS-DOS than CP/M. It would be interesting to port TOS (or more likely EmuTOS) to this 68k IBM PC and kind of go full circle.
- tom_ 3y ago
  The 68000 has a 16 bit data bus. (I always assumed it's 16 bit internally as well? Longword unary register operations take slightly longer than their word equivalents, even though the instruction is the same size in both cases.)
  - mikepavone 3y ago
    > I always assumed it's 16 bit internally as well? Correct, it's mostly 16-bit internally. Registers are 32-bit, but are split into 16-bit halves. The ALU is mostly 16-bit, but has a 32-bit shift register which is used for both shift/rotate operations and multiply/divide. There's a 32-bit adder in the "address unit" that's used for effective address calculations (including the LEA instruction), but it's much more limited than the ALU
krylon 3y ago
IIRC, it was also frequently used for arcade games, and office printers, too.
- rvense 3y ago
  The 68000 is one of the most successful embedded CPUs of all time and you could buy the CMOS varients, 68HC000 and 68SEC000, brand new from NXP until maybe two years ago ago, and derivatives of it (the Coldfire series) are still available - though most or all of them are "not recommended for new designs" now. I think at least some 68ks are still being made by Rochester Electronics, a company that specializes in keeping old chips in production. I have seen 68000's and 68020's in everything from musical instruments to electronic measurement equipment to office equipment and networking hardware made into the late 90's at least. The Coldfire series has probably been all but killed off by small ARM chips for complete new product families now, but I'm almost certain you'd be able to find several of them if you went to your local appliance/electronics store today and started taking stuff apart.
SeenNotHeard 3y ago
As long as we're playing "what if," it's worth reflecting on all the hair-raising hacks and tricks Microsoft had to play to deal with the x86's quirks as they built Windows. XMS/EMS and DPMI were also incredibly painful engineering feats. While the M68K had its own growing pains (as seen with the evolution of the Macintosh), none of them seemed nearly as onerous as what was done to squeeze a few more years out of MS-DOS compatibility.
- StillBored 3y ago
  ? The early mac memory manager in macOS was idiosyncratic to put it lightly. By the time multifinder was integrated into macos, one might say that it was far worse than anything MS was dealing with. I mean at that point they were performing many of the functions we depend on MMU's for these days in software. I guess in a way the complexity of the PC has more to do with the wide range of platforms, software stacks, etc that were being supported more than the architecture itself.
StillBored 3y ago
Realistically in ~1980 or so the "weaknesses" of the x86 weren't so apparent. It was 1/2 way between the 8-biters (6502, 6800, etc) and the newer unproven designs. Back then even the expensive apple /// was limited to 128K of ram and bank switching was common so having the x86 segment+offset was a big improvement. And of course the 8086 was a more mature design, etc. And frankly despite people wanting to rewrite history there was never a time when the 68000 was clearly a better processor. Yes years like 1985 when the amiga was released machines it showed up in looked light years ahead, but software compatibility/optimization/etc meant that within a year or so the PC was either on top or close to it again. It wasn't really until the early RISC machines started showing up that the PC was solidly eclipsed for more than a couple years straight. And many of the technical things people complained about (segmentation, few registers) either were partially false by the time they were complaining about them (ex the 386 provided flat 32-bit addressing in 1985, and even windows/386 was only a year and a half later) or net really a consideration. Ex: pascal/c compilers hid register pressure and caches sped up stack spilling/etc.
- hulitu 3y ago
  > And frankly despite people wanting to rewrite history there was never a time when the 68000 was clearly a better processor. I was amazed to see Domain OS SR9 running on 20 MHz 68020 CPU with 4 MB of RAM a multiuser, multitasking, (GUI), network distributted OS with diskless clients and file versioning.
brian_cunnie 3y ago
Don't forget that Intel had an incumbent advantage: the IBM Displaywriter used the 8086 processor [0]. IBM was already familiar with integrating Intel microprocessors into their equipment. [0] https://en.wikipedia.org/wiki/IBM_Displaywriter_System https://en.wikipedia.org/wiki/IBM_Displaywriter_System

pbj1968 3y ago

Also saw use in soda machines… SEGA genesis…

sprash 3y ago
And Palm devices.
guenthert 3y ago
In the mid to late eighties, the MC68K was also often used in high end (small series) test&measurement equipment, e.g. HP3458A and Datron 1271/1281 DMM, HP166x{A,B,C} logic analyzers ...

cesaref 3y ago

Right, the 68k was the most logical step up from the early 8 bit processors in typical home computers (except for the TI99/4a which went in another direction). They were easy to design for, and easy to program (68k assembler is pretty elegant). The 68008 as mentioned was used in the Sinclair XL, with the 32 bit bus versions in the ST/Amiga/Mac. Initially limited to a 24 bit address bus, but when a machine was topping out at 1Mb, 16Mb seemed a long way away! I think the MMU was introduced with the 68020, which then appeared in early Sun 3s, and HP9000s, prior to the RISC invasion. Those machines seemed super fast at the time.

cmrdporcupine 3y ago
As an Atari ST user, I was a big fan of the 68k back in the 80s but even I'd have to admit that the 808x architecture made the most sense for IBM to take given that it offered continuity with the CP/M S100-bus 8080/z80 machines that were fairly dominant in the nascent "business computing" market at that point. Forking CP/M (cuz let's admit that's basically what PC-DOS was) and offering something similar-but-different to those systems was low-risk. And their original intent in fact was to in fact sell a full-on CP/M machine. FWIW the Atari ST is what you get when you take a CP/M/PC-DOS-style OS and bolt it onto the 68k. Syscalls were basically 1:1 with MS-DOS, and even used an MS-DOS compatible filesystem. But big-endian. If you want to see what an IBM PC built around the 68k would have looked like, that's not far off.
- jdswain 3y ago
  So maybe being a bit pedantic here, but the Atari ST was originally going to use CP/M 68k, but part way through development they changed the base OS from that to what was more of a MS-DOS clone (which as others have said was also mainly a CP/M 80 clone). I think this was done to have better compatibility with the GEM layer, so the Atari ST OS, TOS, was more like MS-DOS than CP/M. It would be interesting to port TOS (or more likely EmuTOS) to this 68k IBM PC and kind of go full circle.
tom_ 3y ago
The 68000 has a 16 bit data bus. (I always assumed it's 16 bit internally as well? Longword unary register operations take slightly longer than their word equivalents, even though the instruction is the same size in both cases.)
- mikepavone 3y ago
  > I always assumed it's 16 bit internally as well? Correct, it's mostly 16-bit internally. Registers are 32-bit, but are split into 16-bit halves. The ALU is mostly 16-bit, but has a 32-bit shift register which is used for both shift/rotate operations and multiply/divide. There's a 32-bit adder in the "address unit" that's used for effective address calculations (including the LEA instruction), but it's much more limited than the ALU

krylon 3y ago

IIRC, it was also frequently used for arcade games, and office printers, too.

rvense 3y ago
The 68000 is one of the most successful embedded CPUs of all time and you could buy the CMOS varients, 68HC000 and 68SEC000, brand new from NXP until maybe two years ago ago, and derivatives of it (the Coldfire series) are still available - though most or all of them are "not recommended for new designs" now. I think at least some 68ks are still being made by Rochester Electronics, a company that specializes in keeping old chips in production. I have seen 68000's and 68020's in everything from musical instruments to electronic measurement equipment to office equipment and networking hardware made into the late 90's at least. The Coldfire series has probably been all but killed off by small ARM chips for complete new product families now, but I'm almost certain you'd be able to find several of them if you went to your local appliance/electronics store today and started taking stuff apart.

SeenNotHeard 3y ago

As long as we're playing "what if," it's worth reflecting on all the hair-raising hacks and tricks Microsoft had to play to deal with the x86's quirks as they built Windows. XMS/EMS and DPMI were also incredibly painful engineering feats. While the M68K had its own growing pains (as seen with the evolution of the Macintosh), none of them seemed nearly as onerous as what was done to squeeze a few more years out of MS-DOS compatibility.

StillBored 3y ago
? The early mac memory manager in macOS was idiosyncratic to put it lightly. By the time multifinder was integrated into macos, one might say that it was far worse than anything MS was dealing with. I mean at that point they were performing many of the functions we depend on MMU's for these days in software. I guess in a way the complexity of the PC has more to do with the wide range of platforms, software stacks, etc that were being supported more than the architecture itself.

StillBored 3y ago

Realistically in ~1980 or so the "weaknesses" of the x86 weren't so apparent. It was 1/2 way between the 8-biters (6502, 6800, etc) and the newer unproven designs. Back then even the expensive apple /// was limited to 128K of ram and bank switching was common so having the x86 segment+offset was a big improvement. And of course the 8086 was a more mature design, etc. And frankly despite people wanting to rewrite history there was never a time when the 68000 was clearly a better processor. Yes years like 1985 when the amiga was released machines it showed up in looked light years ahead, but software compatibility/optimization/etc meant that within a year or so the PC was either on top or close to it again. It wasn't really until the early RISC machines started showing up that the PC was solidly eclipsed for more than a couple years straight. And many of the technical things people complained about (segmentation, few registers) either were partially false by the time they were complaining about them (ex the 386 provided flat 32-bit addressing in 1985, and even windows/386 was only a year and a half later) or net really a consideration. Ex: pascal/c compilers hid register pressure and caches sped up stack spilling/etc.

hulitu 3y ago
> And frankly despite people wanting to rewrite history there was never a time when the 68000 was clearly a better processor. I was amazed to see Domain OS SR9 running on 20 MHz 68020 CPU with 4 MB of RAM a multiuser, multitasking, (GUI), network distributted OS with diskless clients and file versioning.

brian_cunnie 3y ago

Don't forget that Intel had an incumbent advantage: the IBM Displaywriter used the 8086 processor [0]. IBM was already familiar with integrating Intel microprocessors into their equipment. [0] https://en.wikipedia.org/wiki/IBM_Displaywriter_System https://en.wikipedia.org/wiki/IBM_Displaywriter_System