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Thread: How to get a system to boot from a compact flash card?

  1. #11

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    I've found that many older systems require CHS addressing to work, which is a problem with flash media because it uses LBA.
    Oh my, no, just no. Don't worry about that! Flash media don't really care of the drive geometry or media type (fixed/removable; that's purely an OS thing).
    Just think of the many "Raspberry Pi" images (Raspbian, Risc-OS etc) and other disk images which are assumed to be restored on unknown flash cards.

    Compact Flash (CF) in particular was made with embedded and handheld devices in mind from the very beginning.
    Even modern CF cards not only supports IDE (ATA), but also the ancient XT-IDE (8-Bit I/O).
    And three modes (speaking under correction here); normal I/O, memory-mapped I/O and IDE.

    The total memory capacity of a flash medium is the real issue.
    If it's to small, an overrun or other strange things could happen.

    By the way, back in the day you could use a 286 with a type of hardcoded parameters along with a new HDD.
    As long as you used the lowest common denominator, everythjing was fine (as in: not exceeding capacity of the HDD).

    Neither the HDD nor the PC really cared about CHS, E-CHS (aka LARGE) or LBA.
    Beginning with the ~120 MB ATA drives (roughly), everything was virtual, anyway.
    In fact, a few early ATA drives spit out fake CHS values (even fake on label), since the on-board computer was doing translations.

    Hardware wise, old PC's (from the 1980s) might be confused by new CF cards, though.
    Old AT types PC's (286) have outdated BIOSes which don't like the changes made in ATA-2 spec (different behaviuor of certain registers).
    These old BIOSes (pre-1990s) were not even IDE-ware and only supported WD1003 command set used by MFM/RLL drives.
    Also, they are not meant to ever see more than ~500 MB. Same is with MSDOS before version 4 or 5 (such as 3.x) - it behaves strange on big disks.
    In these cases, a BIOS update, XTIDE Uiversal BIOS or a DDO (Dynamic Disc Overlay) software could help, though.

    If you like have a look at these links, maybe they're helpful to you.
    S0KILL erases all data, including that on track 0 (normally inaccessible). It uses BIOS int 13h only (no low-level stuff).
    IDE-DIAG can help to find out the "real" fake geometry of your CF/SD cards.

    https://www.vogons.org/viewtopic.php?p=618884#p618884
    https://www.vogons.org/viewtopic.php?p=607811#p607811

    Drive limits and notes about the FDISK /MBR ancient myths.
    https://www.vogons.org/viewtopic.php?p=762350#p762350
    Last edited by Jo22; September 13th, 2019 at 06:14 AM.
    "Time, it seems, doesn't flow. For some it's fast, for some it's slow.
    In what to one race is no time at all, another race can rise and fall..." -The Minstrel

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