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Thread: why old dos PC's needed a bootable floppy

  1. #1

    Default why old dos PC's needed a bootable floppy

    Hi,

    I remember old school days where we used DOS computers and had to insert a 5' inch floppy to boot the PC, today I wonder why always a floppy was needed to boot and why cant it boot from the hard disk.

    Thanks,
    Zulfi

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    Because there was no hard drive fitted to the machine in question.
    Thomas Byers (DRI)- "You'll have a million people using the A> [MS-DOS prompt] forever. You'll have five million using [nongraphic] menu systems such as Topview, Concurrent PC-DOS, Desq, and those types. But there'll be 50 to 100 million using the iconic-based interfaces."

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    Indeed, I know of a few older (pre-PC) systems where booting could not be performed from the hard disk, but had to be done by floppy or (older) tape or cards.

  4. #4

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    That is what keeps me wondering why boot could not be performed from hard disk

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    Well, with the Wang system I used back in 1982, the boot floppy contained login information instead of having the minicomputer display a prompt. Was supposed to make unauthorized entry slightly more challenging.

    A lot of PC based educational software was designed to be launched from bootable diskettes to prevent the student from doing anything else which became a bit silly as the systems being purchased had hard disks that never saw use.

    For some older systems, the design happened before the hard disk was available. The boot can only happen with the devices the system knew about. Not having worked with the 1960s era mainframes I don't know if it really was as Rube Goldbergish as sometimes described where switches are flipped which activates the (paper) tape or card which then transfers control to fast storage that contains the software and operating system users would recognize.
    Last edited by krebizfan; September 6th, 2013 at 09:18 PM.

  6. #6

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    Quote Originally Posted by Chuck(G) View Post
    Indeed, I know of a few older (pre-PC) systems where booting could not be performed from the hard disk, but had to be done by floppy or (older) tape or cards.
    The first two ROM BIOS revisions of the IBM PC don't support booting from a hard drive, either. There were some aftermarket hard drives released for the PC during that time, but they required a boot disk.

    As quoted from a Usenet post dated 1986, "If you have an older PC, with 64K on the motherboard and a serial number under 300,000, you need to get the hard disk BIOS from IBM, 'BIOS Kit ROM Module', P/N 1501005, to boot from the hard disk."

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    ROMs were small and not very general in the old CP/M days. You were lucky in the old mainframe days if you even had any sort of ROM. Here's the "ROM" of a system I used for years:



    On my S100 system, at first I had a 32-byte bipolar ROM. Not nearly enough for a hard disk boot.

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    DEC sold diode matrix boards that could hold enough code to bootstrap the system.
    = Excellent space heater

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    Quote Originally Posted by zulfi123786 View Post
    That is what keeps me wondering why boot could not be performed from hard disk
    I thought "Because there was no hard drive fitted to the machine in question" and/or "The first two ROM BIOS revisions of the IBM PC don't support booting from a hard drive" explained it rather well...

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    Quote Originally Posted by NeXT View Post
    DEC sold diode matrix boards that could hold enough code to bootstrap the system.
    Sorta like this? :
    Dmatrix.JPG
    That's a 10x13 inch PROM

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