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Pastimes : Dream Machine ( Build your own PC ) -- Ignore unavailable to you. Want to Upgrade?

To: pae who wrote (5483)	1/22/1999 10:08:00 AM
From: Spots	Respond to of 14778

I gotta tell ya ... Mobos vary as to whether they autodetect EIDE CDROMs (or at least whether they report the fact). There's no reliable test for access to a CD other than accessing the CD. Well, I suppose if you observe the cable has been clipped in two, that's a fairly reliable indication you aren't going to get too far <g>. It's a file-system thing, anyhow. The bios has to figure out the HD geometry (sort of, more below) in order to perform accesses -- so many sectors per track; so many heads (tracks per cylinder); so many cylinders on the drive -- so it can figure out how to get to sector 88392, for example. Not so CD roms. With exception of the bootable ones, which specs are laid out in some rainbow book or other, CD roms are a mystery to the bios (well, the bios can read out the manufacturer's ID, but I think that's an (E)IDE thing, not a CD thing). CD rom access depends on the OS which has to find a driver that knows the color book the CD was scribbled from, or no CD access. I don't know that the bios EVER has to detect a CD in order for an OS driver to get at it, but I admit that may not be true in all cases. I don't know if the folks having such problems here tried the actual CD when the bios didn't report it, but as you found out it's definitely not always true. On HD geometry: Modern hard drives lie to the bios about their geometry. More and more is getting squeezed into fewer and fewer platters, but older bioses have small boxes for sectors per track, tracks per cyl, etc. So the drive lies and says it has, say, 63 sectors per track (when it really has 6400), 16 tracks per cylinder (when it really has two), 63000 cylinders (when it really has 6300). The game is to fill the sector count and head count boxes so the drive capacity is reflected in the cylinder count. When the cylinder count box overflows, the bios can't get at the higher part of the drive. As an aside I should add that various Windows flavors do their own sector mapping rather than using the bios except at bootup.