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5458Re: Designing Vintage Hardware (was Altair 680 Basic - loading without paperta

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  • Herb Johnson
    May 8, 2007
      David Comley <david_comley@...> wrote:
      > I'm hoping to be able to emulate a Micropolis 1325 at
      > a low enough level that it could support any
      > host/controller platform (that can use that particular
      > drive type/geometry etc). The drive emulation should
      > be transparent to the point where any low level format
      > can be overlaid on it by the controller or host.
      > Doing an emulation of an MFM drive would be useful for
      > a variety of reasons for hobbyists, not the least of
      > which is the cost of replacement drives. The MTTF of
      > the platters in these drives is 4 years so they are a
      > dying breed; plus, emulation would make it possible to
      > expose the low-level formatting used by the hardware
      > vendor, something that there's not a great deal of
      > documentation on so far as I can tell.
      > Of course talking about it is easier than actually
      > doing it...
      > -Dave

      There was a recent discussion of MFM "emulation" in comp.os.cpm, where
      I participate. The discussion of "vintage" vs. "modern" design is also
      of interest to me. Here's my comments.

      In comp.os.cpm, it was noted that there WAS a MFM to IDE product, but
      it waa a few thousand dollars. Seems to me that one reason it is that
      high, is that it takes some bit of effort to support the variety of
      potential uses for such a product. Those who really need an MFM
      replacement, to keep production equipment going, will pay accordingly.

      The drive issue as cast in comp.os.cpm was about replacing an MFM
      drive in a S-100 system. It was suggested the owner use an IDE card of
      some sort, and write a driver. In some number of cases, it's more
      reasonable to replace the controller and adjust the software.

      The point of S-100 systems with a standard bus, was that you COULD
      replace and upgrade as needed. At least the hardware did not stop you
      from doing so. That concept spawned a computer industry from 1976
      through the 1980's. The IBM PC, to compete, HAD to offer 1) a bus and
      2) clear means to add to that bus - because S-100 and other systems
      set that standard. (In the minicomputer world, DEC set a similar
      standard as did other manufacturers.)

      In that light, there's been discussion here about building "new" S-100
      cards with either "vintage" hardware or with "new" hardware. Clearly
      an MFM to IDE device would be "new". It would require somewhat fast
      logic: either a programmable logic device, or a "computer on a

      But an IDE interface for S-100 or any Z80? - dirt simple, the IDE
      drive does all the work, just a few simple chips will do it (Google
      "GIDE"). But most people get stuck at the point where they have to
      write software to support that new device. (I should know, I first
      offered the GIDE interface in the USA, and I've watched its use.)

      Note to "purists" that say a vintage system has to have "original",
      vintage cards. Few REAL S-100 systems were "original", or stayed
      original. People upgraded as hardware improved, as software changed.

      The point? As I see it, if you are "into" old computers to show them
      off in original condiiton, then all this talk about "emulators" is
      moot. Pay $$$ for the last unused (or rebuilt) MFM hard drive and run
      it only on exhibit day. If you are in it because you can "dig into"
      it, then adapt some new hardware to old and start writing some CODE.
      If you are in it for "use" only, then you depend on others to keep
      providing working hardware: that, and your budget.

      Herb Johnson

      Herbert R. Johnson, New Jersey USA
      <a href="http://www.retrotechnology.com/herbs_stuff/"> web site</a>
      <a href="http://www.retrotechnology.net/herbs_stuff/"> domain mirror</a>
      my email address: hjohnson AAT retrotechnology DOTT com
      if no reply, try in a few days: herbjohnson ATT comcast DOTT net
      "Herb's Stuff": old Mac, SGI, 8-inch floppy drives
      S-100 IMSAI Altair computers, docs, by "Dr. S-100"
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