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Thread: Magical hidden 40K of space on 1.44MB floppies or pure snake oil???

  1. #11
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    The ones that I've tried do. If you look around in SIMTEL20, you may actually find one or two of my DOS device drivers for HP150 and HP150 Series II systems. I didn't add the extra sector in the formatting routine and they appear to work just fine.

    I don't believe that the HP110's floppy drive, the HP9114B cares whether or not the extra is there either.

  2. #12
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    This reminds me of how 400/800k Macintosh formatted disks actually have 524 mutable bytes per sector (the extra 12 are "tag bytes") but the Macintosh OS almost universally didn't care about them. (They're a leftover from the Lisa file system and were intended to serve as a sort of backup file recovery mechanism in case the directory was corrupted, but the Mac had only rudimentary application-level support for setting them which was basically completely depreciated when Macs started getting hard disks.*) Technically the "Disk Copy 4.2" image format can preserve any contents of the tag bytes but most emulators and whatnot completely ignore them with no ill effect.

    (* The weird floppy-port-connected HD-20 hard drive being possibly the only exception; it actually had 532 byte physical sectors to accommodate 20 tag bytes, again a leftover from being descended from the "Widget" Lisa HD. Likewise I don't think anything actually *used* them, but I suppose technically you might be able to ferret away some secret information in the space?)
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  3. #13
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    Well, the old Zilog MCZ encoded 132-byte sectors on their 8" floppies. The extra 4 bytes were used as a forward- and back- link for files.

    Never caught on, for some strange reason.

    There's a bit of precedent for even that. CDC 60-bit mainframes recorded 644 characters per sector on the disk drives. (one word was 10 characters) The extra 4 characters was used to differentiate between end-of-record and end-of file (either could have a level number attached to it).

  4. #14

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    In the DOS days I often used a TSR called INT13X which allowed 1.7MB or so on a normal 1.44MB floppy. It worked pretty well.

    After I'd gotten myself Windows 95, I discovered that it natively supported the use of the expanded disk (read & write, not format). I guess not many people would have expected that.

  5. #15
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    Yes it works. Atari users did this often, but remember its the inner two tracks so the density is above what the disk is specified to. Given I find the higher numbered tracks less reliable, I would think these will be the first into the great bitbucket in the sky...
    Dave
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  6. #16

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    Quote Originally Posted by Shadow Lord View Post
    So I was perusing some old freeware/shareware collections and ran across a program that promises access to a hidden 40K of space on 1.44MB drives. From the readme:
    Code:
    Extraterrestrial Floppy Magic (ET.EXE) for DOS and WINDOWS ver 1.0
    I'd like to try this in emulator and see what it does. Can you upload this somewhere or post a link to the collection where you found it?

  7. #17

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    Quote Originally Posted by SomeGuy View Post
    Those tracks are "undocumented" in the sense that floppy drive vendors didn't include those in their specifications and the actual max track can be different between two seemingly identical drive models.

    I seem to recall that the 3.5" citizen drive in my Kaypro 2000 would not step beyond the 80th track, although that may have been BIOS stopping it. As far as I know, anything beyond the 80th track is just there as a mechanical margin for error.

    I've wondered about that. I've seen that in some HP 150 disk images, figured that was a holdover from something.
    Do you guys happen to know how data can be extracted from such images? They're seem to be out there in Teledisk format, but attempts to convert them to IMD or raw formats for extraction (e.g. using Samdisk) fail, since those formats do not handle mixed sector sizes in a single track.
    int10h.org :: :: :: blog

  8. #18
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    If a Teledisk image has mixed sector sizes, the image may be either non-IBM PC or copy protected and extracting data from it may be pointless.

    That said, try the HxC software tool. It can load .TD0 images.

    Quote Originally Posted by shattered View Post
    I'd like to try this in emulator and see what it does. Can you upload this somewhere or post a link to the collection where you found it?
    Be aware that many emulators do not support anything outside of standard 360k/720k/1.2mb/1.44mb disk images.

  9. #19

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    Quote Originally Posted by SomeGuy View Post
    If a Teledisk image has mixed sector sizes, the image may be either non-IBM PC or copy protected and extracting data from it may be pointless.

    That said, try the HxC software tool. It can load .TD0 images.
    Thanks. Those are HP 150 disks; code extracted from those may be useless, but data not necessarily so.

    Quote Originally Posted by SomeGuy View Post
    Be aware that many emulators do not support anything outside of standard 360k/720k/1.2mb/1.44mb disk images.
    Yep. I can't think of a publicly available emulator that consistently implements the full behavior of a floppy controller. Reportedly 86box gets close if you're using its specific image format, but I can't be sure.
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  10. #20
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    The PCE emulator can also handle odd formats when using its .PSI sector image format. It is very good emulation but has some limits, such as timing.

    Since it does not limit the track length, it is possible to get away with formatting murder. I just tried formatting a PSI floppy image using 63 sectors per track, two sides, and 255 tracks. It actually worked!

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