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Thread: Why does the 5.25 drive/controller in the 5170 ve such an elaborate startup sequence?

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    Default Why does the 5.25 drive/controller in the 5170 ve such an elaborate startup sequence?

    I grew up mostly with a 5170 as a kid and always for some reason loved the unique startup/init sound the floppy makes when it powers up. To me it has always seemed much more elaborate than other systems. It takes close to 5 or 6 seconds! Always wondered if that was just IBM going the extra mile to self diagnose and check everything or just the nature of the drive, whoever made it.

    Anyone else find the 5170 to be particularly distinctive on this point?

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    Most of the stuff is verifying the drive presence and type. Also, note that the spin-up time in the BIOS is spec-ed (IIRC) at 2 seconds.

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    Curiously it does this even without the presence of a bios battery... I wonder how it would know what to check for, since you have to use the setup disk to tell it what is there.

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    It checks for several things among others:

    1. Is there a drive present?
    2. Does it have more than 40 tracks?

    The idea is that even if your "CMOS" is set up incorrectly, that you'll still be able to boot from floppy. As the 5170 doesn't have an interactive BIOS setup in ROM, it has to be able to boot a configuration program.

    Since the configuration is usually a "360K" floppy, the BIOS needs enough information to set the data rate (250K vs. 300K) and double-step or not.

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    I don't know about the later versions, but at least the earlier editions of Inside the IBM by Peter Norton went into what needs to be checked before anything interesting happens. You'd be surprised by the amount of checks needed.

  6. #6
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    At one point, I was curious as to what the IBM 5170 could be booted from when the ("CMOS") SETUP was in an uninitialised state.
    In such a condition, all three revisions of the BIOS allow booting from either 360K or 720K, with the third revision adding the ability to also boot from 1.44M

    I documented the 720K/1.44M information at the bottom of [here].

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