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IBM PC 8088 replaced with a Motorola 68000

123 点作者 elvis70大约 2 年前

19 条评论

klodolph大约 2 年前
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.<p>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.<p>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.
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gallier2大约 2 年前
Take an Atari ST and you can see what a m68k PC could have been. Its operating system GEMDOS was a derivative of CP&#x2F;M with comparable features of MS_DOS. The syscall even use the same numbers (trap #1 calls to GEMDOS map 1:1 on int 21H MS-DOS calls).<p>This said, several hardware PC-emulators on the Atari did exactly the thing that article describes. PC-Speed added a NEC V30 that was soldered on the 68000 and could takeover the bus and the emulation only consisted on simulating the peripherals. It worked like a charm and thanks to the generous memory of the ST could even do some things better than real PC&#x27;s (for example the 640K limit was in reality a 736K limit). Later versions used 286 and even 386sx cpu&#x27;s.
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mikewarot大约 2 年前
Oh man, 15 registers, each 32 bits wide, with indirect addressing modes... it would have been glorious! No more weird need to cram things into just the right registers to do a string operation.<p>Not as nice as a PDP-11 processor, but damned close!
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agar大约 2 年前
I always thought that if the same amount of engineering and investment that went into overcoming the 8088 architecture instead was redirected into a more sane CPU architecture, development of the PC industry would have been accelerated by about a decade.<p>I&#x27;m talking products like QEMM, Sidekick (and the whole &quot;terminate and stay resident&quot; industry), expanded vs. extended memory, and other massive engineering efforts by major software (Lotus, Ventura Publisher, etc.). Time spent overcoming the limitations of the 640K barrier, segmented memory, and similar design challenges could have been spent in more productive ways, as could be seen in the development of other ecosystems on a comparative shoestring budget.<p>Granted I was an Amiga aficionado back in the late &#x27;80s&#x2F;early 90&#x27;s, so I&#x27;m comparing things like the ATI VGA Wonder (1988) to the Video Toaster (1990), or early efforts at GUIs (like GEM) to the multitasking OS of Amiga. But still, I think the point stands.
skissane大约 2 年前
&gt; It could also have been the case that Microsoft did not have an operating system or BASIC ported to the Motorola 68000 architecture.<p>The late 70s &#x2F; early 80s incarnation of Microsoft was happy to port their software to just about anything, so long as there was a customer willing to pay for it. If IBM had asked Microsoft for a 68K OS instead of an x86 one, Bill Gates would have found a way to provide. He bought PC&#x2F;MS-DOS from another company, he probably could have found someone selling a 68K OS instead. Or Tim Paterson surely could have ported it to 68K if asked.<p>I think choosing the 8088 over 68K was all about hardware costs, not software-both the cost of the CPU, and the cost of compatible peripheral chips.
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klelatti大约 2 年前
IBM, of course, did use (re-microcoded) 68000’s in a PC product - the XT&#x2F;370. With a modified 8087 on a couple of cards these were used to emulate an S&#x2F;370.<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;PC-based_IBM_mainframe-compatible_systems" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;PC-based_IBM_mainframe-compati...</a>
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exsf0859大约 2 年前
Cool hack! Also interesting that the performance is no better, presumably due to the lack of cache.<p>The first answer on this forum post has what is probably the correct explanation for why the 8088 was chosen:<p>It was available, had a second source, and was not owned by a competitor.<p><a href="https:&#x2F;&#x2F;retrocomputing.stackexchange.com&#x2F;questions&#x2F;16912&#x2F;did-ibm-originally-plan-to-use-the-68000-in-the-pc" rel="nofollow">https:&#x2F;&#x2F;retrocomputing.stackexchange.com&#x2F;questions&#x2F;16912&#x2F;did...</a><p>Although ease-of-translation from 8080-based CP&#x2F;M code was a benefit of choosing the 8086, this was just a nice-to-have, not a deciding factor.
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kazinator大约 2 年前
&gt; <i>It could also have been the case that Microsoft did not have an operating system or BASIC ported to the Motorola 68000 architecture.</i><p>That would be a big thing. 8088 assembly language is source-code compatible with 8080 assembly language. I believe IBM was eyeing the ability to run CP&#x2F;M and derivatives like CP&#x2F;M-86. IBM&#x2F;MS DOS is basically a CP&#x2F;M-like, derived from this:<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;86-DOS" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;86-DOS</a><p>&quot;[86-DOS&#x27;s] application programming interface was very similar to that of CP&#x2F;M. The system was licensed and then purchased by Microsoft and developed further as MS-DOS and PC DOS.&quot;
dmitrygr大约 2 年前
On an 8 bit bus the 68k is almost useless. I am currently working on a project that involves that and looking at the logic analyzer trace is just tear-inducing. 68k has a terrible IPC to start with, and sticking it on a narrow bus cuts it by more than half. You’d be lucky to squeeze 0.8MIPS out of a 16MHz 68k on a 8 wide bus. Mainly the cause is the fact that the smallest possible instruction is 2 bytes. And it will take at least 4 cycles to fetch it (68k will execute a compete nCS cycle PER BYTE - no bursts to be found here).
tyingq大约 2 年前
That&#x27;s really impressive, that the emulated M68K is socketed in the 8088 motherboard and talking to all the peripherals through it.
phkahler大约 2 年前
Not sure about the authors performance claims. He doesn&#x27;t indicate how fast his emulated 68000 is in terms of MIPS or equivalent MHz. It&#x27;s also constrained by the 8bit bus which might have been wider if IBM had chosen that chip. Certainly would have been wider by the 286 equivalent generation.
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ok123456大约 2 年前
During the initial meetings about the IBM PC, didn&#x27;t Microsoft pitch the idea of using the 68k?
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zwieback大约 2 年前
I vividly remember how sad I was when IBM chose the 8088, should have been 68K.
cmrdporcupine大约 2 年前
Author should port EmuTOS to it. Or at least just EmuCON, the console-only variant (basically GEMDOS)<p><a href="https:&#x2F;&#x2F;emutos.sourceforge.io&#x2F;" rel="nofollow">https:&#x2F;&#x2F;emutos.sourceforge.io&#x2F;</a>
sitkack将近 2 年前
This is an awesome post, but I don&#x27;t think it proves that it wouldn&#x27;t have mattered. The biggest win with 68k over 8088 is the flat address space and the innovations that would have been easier with a larger address space. The PC was super constrained from a software perspective because of segment registers and the memory model.
stefric大约 2 年前
Don’t you love geeks…<p>This was a simple and fun read while waiting for my coffee to be done. I also wonder how the world would look if IBM partnered with Apple rather than Microsoft.
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ch_123大约 2 年前
IBM also had experience of the 8085 and 8086 from their System&#x2F;23 and Displaywriter systems which meant there was previous experience with Intel microprocessors in IBM at that time. I also read somewhere (but do not have a source to hand) that IBM had a significant investment in Intel at that point in time.
Dwedit大约 2 年前
If you wanted to run 68000 code as fast as possible, nowadays you&#x27;d use a recompiler emulator.
randombits0大约 2 年前
I like this guy. He does strange things with hardware. Z80 on a Teensy 4? No problem!