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Thread: Wipe hard disk on Tandy 1000 SX

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    Default Wipe hard disk on Tandy 1000 SX

    How do I wipe the hard drive on a Tandy 1000 SX so I can sell it? The computer only has 5.25" drives, so I am not even sure how to transfer wiping software onto the tandy from a modern computer.

    Or should I just physically destroy the hard drive? The computer is fully functional including monitor, keyboard, joystick and two printers.

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    Quote Originally Posted by bacon4life View Post
    How do I wipe the hard drive on a Tandy 1000 SX so I can sell it? The computer only has 5.25" drives, so I am not even sure how to transfer wiping software onto the tandy from a modern computer.

    Or should I just physically destroy the hard drive? The computer is fully functional including monitor, keyboard, joystick and two printers.


    Please don't destroy the hard drive if it works well. Are you certain it HAS an actual "hard drive?" Does it boot up to a C:\ prompt?

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    Assuming your Tandy 1000 SX even has a hard disk at all (it would have to have been an add-on since the 1000SX didn't come with one originally as far as I recall), it will be enough to just delete all your personal files from the C: drive, then to ensure they aren't recoverable fill up the drive by making multiple copies of the DOS directory until there's no space left.

    In practice, "wiping" data actually means overwriting the data with something uninteresting, and that's something you can do without any special software beyond what DOS itself provides. If you're a bank, a government agency, the military, or anything like that you might need to overwrite the data multiple times but that's to protect data from a determined enemy with government-level resources at their disposal. A single overwrite is enough to protect your data from any regular person. You don't need a military-grade secure wipe for something as basic as personal financial or health information.

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    If you have the ability to boot to DOS on a floppy disk, you can wipe the drive using DOS debug.

    debug
    a
    mov ax, 309
    mov cx, 1
    mov dx, 80
    int 13
    int 20

    g

    then reboot.

    This doesn't perform a full disk wipe, but would be enough to make the next user of the hard drive have to re-partition, format, and install their own operating system, which will in turn cause enough re-writes to the drive to effectively destroy any of the old data on it.

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    I have a feeling the OP is gone forever, but since debug was mentioned I suppose if we knew the make and model of the controller we could add to the list that many XT hard drive controllers have a low-level format routine built into their BIOSes. You can usually access it by jumping to an entry point with Debug.

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    Quote Originally Posted by hargle View Post
    If you have the ability to boot to DOS on a floppy disk, you can wipe the drive using DOS debug.

    debug
    a
    mov ax, 309
    mov cx, 1
    mov dx, 80
    int 13
    int 20

    g

    then reboot.

    This doesn't perform a full disk wipe, but would be enough to make the next user of the hard drive have to re-partition, format, and install their own operating system, which will in turn cause enough re-writes to the drive to effectively destroy any of the old data on it.
    I don't do assembly but out of curiosity I tried to figure out what this code does.

    You move 309, 1, and 80 to AX, CX, DX registers, then invoke int 13.

    Int 13 uses the DX value (80) to specify to operate on first hard disk in system?

    Not sure what AX and CX do, are they writing 309 instances of the number 1 to overwrite boot sector/partition table/file allocation table?

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    Quote Originally Posted by keenerb View Post
    I don't do assembly but out of curiosity I tried to figure out what this code does.

    You move 309, 1, and 80 to AX, CX, DX registers, then invoke int 13.

    Int 13 uses the DX value (80) to specify to operate on first hard disk in system?

    Not sure what AX and CX do, are they writing 309 instances of the number 1 to overwrite boot sector/partition table/file allocation table?
    INT 13 relies on values in the registers to perform its functions. You load the registers with values, then invoke the function with the INT instruction. AX is divided into AH and AL. AH is 3, which specifies the function Write Sectors to Drive. AL is 09, which means write 9 sectors. CX is divided into CH and CL, and they specify the cylinder number (00) and the sector number (01). DX is divided into DH and DL, and they specify the head number (00) and the drive number (80=1st Hard Drive). This will appear to write garbage (more specifically whatever data ES:BX is pointing to) to the first data area of the disk (cylinder 0, head 0, sectors 1-9) and wipe the Master Boot Record, including the bootstrap and the partition table and the Boot Sector of the primary file system. INT 20 terminates the program, presumably because such vandalism may cause a freeze otherwise.
    Last edited by Great Hierophant; September 12th, 2019 at 11:08 AM.
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    Int 26h can be used to wipe the data on a partition also. Somewhat easier to use as it uses relative block addresses rather than CHS. Just keep writing until you get an error. It doesn't wipe the partition table information, but that's unlikely to contain sensitive data.

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