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

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  • joshbensadon
    ... Why is that? I m wondering why does a SD head care if it s a DD or SD disk? I m not doubting this, just wondering why. I remember the days of DOS and
    Message 1 of 40 , Dec 14, 2012
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      --- 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?

      I'm not doubting this, just wondering why.

      I remember the days of DOS and how 360K disks (formatted on a 360K Drive) didn't work (for the most part) on 1.2M drives. The 1.2M drives were suppose to be able to be backward compatible with those DSDD 5.25 disks. Right?
    • 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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