Puzzling thing about bios boot sequence

  [DELETED] 11:39 25 Jan 2006

Got a (slightly) panicky call from a friend last night,saying that he'd turned his machine on and it just came up with invalid system disk. About 2 seconds later I told him to eject his floppy, and reboot. problem solved. However, because I was suffering at the time from an attack of the dreaded cleverideaitis, I talked him into going into bios and changing the boot up sequence to prevent it from happening again. it was set to cdrom,A,C and I got him to reverse it to C,A,cdrom. all well and good until I told him why. then he came out with something which frankly has me baffled.

If there was no cd in D drive, it would go looking in A drive. If there was something in in D drive, it would spin it up, look at it, decide it wasnt going to get any start up files from there and move on to A.

If there isnt a floppy in, then it will go to C and boot normally. yet with a non bootable floppy in A the boot stalls, and will not go to C (the next drive in the sequence).

Ive known that this is normal, but I havnt a clue why bios will ignore an irrelevant cd, but not a floppy disk.

This isnt a problem as such, more a curiosity bump that needs scratching. Anyone care to oblige?


  xania 12:46 25 Jan 2006

Don't know, but I suspect the logic may go something like this. When PCs first came along, the floopy boot process was written and its not been touched since - by the time the CD version came along, others realised that CDs can be left in the PC which would not be bootable and hence wrote more sophisticated code. In fact the latest code, when it identifies a bootable CD AND a bootable Hard Drive, gives you the option of which to use - wouldn't it be wonderful. But hey - many PCs now come without a floopy drive so there you go.

  Stuartli 15:16 25 Jan 2006

It sounds as though your friend either has either not set the correct sequence or didn't Save and Exit the changes after making them.

  [DELETED] 19:33 25 Jan 2006


You've missed the point here. What I'm saying is that a pc with cdrom as first boot will ignore a non bootable cd and go onto the next boot device. this cannot be said of a floppy drive. The above tale was merely to explain what got me wondering about it in the first place.


  [DELETED] 19:48 25 Jan 2006

Never thought about it either WhiteTruckMan. Perhaps its something to do with the way floppys were designed to work at the time? They have been about for a long time now and haven't changed whereas hard drive technology has moved on considerably. And CD ROMs are relatively new as well.

  [DELETED] 19:49 25 Jan 2006

I agree - I think it's a legacy thing.

  Stuartli 21:07 25 Jan 2006

No, I haven't missed the point as far as I am aware.

A bootable CD is (normally) an OS installation disk. I use my XP Pro disk as the Boot from CD on the odd occasion I've had to Repair XP.

A floppy drive with a non bootable disk in it on bootup used to (IIRC) prevent the bootup at all.

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