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hard drive analysis - XT controllers

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  • Jim Scheef
    Bill, True XT-style controllers had the drive geometry in ROM and thus each controller would only support a very limited number of drives (as many as three -
    Message 1 of 3 , Jul 3, 2006

      True XT-style controllers had the drive geometry in ROM and thus each controller would only support a very limited number of drives (as many as three - sometimes selected by jumper!). The initial AT controller was a little better in that the drive geometry tables moved to the computer's ROM BIOS. This allowed support for more drives but the tables were obsolete before the first machine was sold. The present situation came about when the BIOS manufacturers realized that a complete table was impossible and allowed for two "user defined" drive types. These are still with us but the BIOS and the drives have become smart enough to fill in the blanks for us.

      So back to your XT era drives... a drive that come up 'bad' simply may not be supported by your controller. I would move to an AT-style motherboard and controller where you can enter the drive geometry into the BIOS settings.

      Herb is correct that most (perhaps all) MFM and RLL controllers had a low level format built into the adapter ROM. I believe this was usually found at C800:xxxx (hey I remembered all this so far). Your favorite search engine, an old book, or some documentation can fill in the exact address, however, once you have the controller talking to the drive with the correct numbers of heads and cylinders, SpinRite will recognize the drive and you're on your way.

      As to moving a drive from one system to another... A fresh low level format (remember when it was the rage to reformat your drive to change the interleave from 3 or 4 to 1?) would erase any remnants of an incomptible partition table.


      ----- Original Message ----
      From: Herb Johnson <hjohnson@...>
      To: midatlanticretro@yahoogroups.com
      Sent: Monday, July 3, 2006 11:51:29 AM
      Subject: [midatlanticretro] Re: correction - hard drive analysis

      --- In midatlanticretro@ yahoogroups. com, "B. Degnan" <billdeg@... > wrote:
      > For the IBM XT you need to use the reference disk to format the hard
      > if it's from an alien system. I should have thought of that being
      an ex
      > IBMer...but it's been a while. In the process of formatting a drive
      > Bill
      Bill, as I remember XT's and MFM controllers, many of those
      controllers had a "low level format" routine in their BIOS ROM. That
      routine was accessed by using DEBUG and starting at a ROM address,
      something like C300:0005. A Web search on those terms should find this
      info. POWER THE DRIVE FOR SEVERAL MINUTES before doing this, so it's

      A low level format will rewrite all tracks and sectors. I recommend it
      so that any marginal tracks can be recovered. However this may also
      wipe out any info about "bad" tracks found by previous use.
      Consequently a reasonable next step is to use a program to test and
      mark bad tracks, perhaps the program you mentioned.

      The problem is that relative to drives today, the old MFM drives had
      limited self-diagnostics. Also becuase of their advanced age, they
      will be marginal and have physical errors, probably. For any serious
      use of such drives, they should be reformatted and tested THROUGHLY.

      Can you format under MS-DOS and use on DEC or other OS's? Low level
      formats are not OS dependent; they CAN be controller-dependen t. High
      level format which determines drive partitioning IS OS dependent.
      Features like "bad blocks" may or may not be OS dependent. Best
      practice is to low level format and partition on the destination OS
      and controller - but testing on a more demanding controller and OS is
      a good idea!

      Other MARCH associates know more about MFM drives than me and can
      probably advise you, or more likely remind you of tricks you learned
      and forgot.

      Herb Johnson

      Herbert R. Johnson, New Jersey USA
      <a href="http://retrotechnol ogy.com/herbs_ stuff/"> web site</a>
      <a href="http://retrotechnol ogy.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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