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Re: [midatlanticretro] Re: New 8" system works (was Lobo floppy drives)

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  • Richard Cini
    ... This is one fact that I didn t know and was the cause of my issues (apparently). I didn t realize there was a difference so I was chasing down several
    Message 1 of 40 , Dec 14, 2012
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      >>The index hole aperture in an single-sided 8" disk is in a different location 
      >>than on a double-sided disk. 

      This is one fact that I didn't know and was the cause of my issues (apparently). I didn't realize there was a difference so I was chasing down several different paths.

      Rich

      --
      Rich Cini
      Collector of Classic Computers
      Build Master and lead engineer, Altair32 Emulator


      From: Mike Loewen <mloewen@...>
      Reply-To: "midatlanticretro@yahoogroups.com" <midatlanticretro@yahoogroups.com>
      Date: Friday, December 14, 2012 6:53 PM
      To: "midatlanticretro@yahoogroups.com" <midatlanticretro@yahoogroups.com>
      Subject: Re: [midatlanticretro] Re: New 8" system works (was Lobo floppy drives)

       

      On Fri, 14 Dec 2012, joshbensadon wrote:

      > --- In midatlanticretro@yahoogroups.com, Richard Cini <rich.cini@...> wrote:
      >>
      >> All --
      >>
      >> Today I was able to get my 8" Lobo drives working with my IMSAI. Whoo Hoo!
      >> What was giving me fits was that the drives weren't going "ready". Where I
      >> went wrong was that I was using DSDD disks for testing and not SSSD disks. I
      >> figured that the sides wouldn't matter but I was mistaken in thinking that
      >> the DD disks were backward-usable on the SD drives. Once I dug out SSSD Type
      >> 1 disks, everything worked. Yea!
      >
      >
      > Why is that? I'm wondering why does a "SD" head care if it's a DD or SD disk?

      It's not the density that matters, but single or double sided. The
      index hole aperture in an single-sided 8" disk is in a different location
      than on a double-sided disk. Double-sided drives will typically have two
      index hole sensors: one for single-sided and the other for double-sided.

      Mike Loewen mloewen@...
      Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/

    • Mike Loewen
      ... Here s the service manual for the Tandom TM-848, with the schematics in the back: http://bitsavers.trailing-edge.com/pdf/tandon/TM848_service_1982.pdf
      Message 40 of 40 , Dec 15, 2012
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        On Sat, 15 Dec 2012, joshbensadon wrote:

        > --- In midatlanticretro@yahoogroups.com, Mike Loewen <mloewen@...> wrote:
        >>
        >> The double-sided drives have a 2S signal on pin 10 of the interface
        >> connector to indicate single or double-sided media. The outputs of the
        >> respective pulse-shaping ciruitry for each sensor is essentially ORed to
        >> form a single Index pulse output.
        >
        >
        > Cool, so I can imagine the two sensor signals going to an RS flip flop
        > to provide the 2S signal and as you said to an OR gate for the index.

        Here's the service manual for the Tandom TM-848, with the schematics in
        the back:

        http://bitsavers.trailing-edge.com/pdf/tandon/TM848_service_1982.pdf

        Knock yourself out. :-)

        > Hmm, thinking about why, I guess the design was to create a hardware
        > error if a user placed a DS disk into a SS drive. As Rich found, the
        > lack of index pulses caused a drive not ready. Correct me if I'm wrong,
        > but in later 5.25" drives, they did not change the index sensor
        > location. Then I suppose the errors created would be software
        > generated?

        The 5.25" drives only had a single index hole aperture.

        > I vaguely remember hearing a discussion about how computers switched
        > from hardware solutions to software solutions, then back to hardware.
        > I just don't know the dates, could this 8" to 5.25" be part of that
        > switch?

        I couldn't say. Certainly Woz did a lot in software for his Apple II
        disk controller design. Another odd thing about the 8" drivers vs the
        5-1/4" drives was that the 8" drives had a write-enable notch, while the
        5-1/4: drives had a write-protect notch. Very confusing.


        Mike Loewen mloewen@...
        Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/
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