Jonathan Sachs wrote in message
...
Rod Speed wrote

I will have at least three IDE devices: two hard disks
and a CD/RW or DVD drive. I'm assuming that each
device should go on a dedicated channel.

No need.

That seems to require some explanation.

The short story is that its only simultaneous ops on a pair of drives
that benefits from having that pair on a separate channel. Thats
pretty uncommon in practice. The most common real world situation
where thats seen is when ghosting one drive to an image file on
another drive and even then, the speed of that operation is
dominated by the compression time if compression is used.

Even when say burning a CD from a hard drive, the speed
of the entire operation is mostly determined by the speed of
the burner which is much less than the speed of a hard drive.

I said "I'm assuming" because I know that an IDE
channel can perform only one operation at a time.

Yes, but the modern reality is that you dont often use two drives
literally simultaneously. And you never use 4 drives simultaneously,
so there isnt any need for them all to have their own channel.

Even SCSI doesnt allow the use of all 4 drives simultaneously anyway.

Thus if two devices share a channel, any
operation on one device will lock out the other.

Only if both are being used at once.

Thus if a DVD drive is seeking, for example, a
read or write request on the hard disk will jolly well
have to wait until it's done. Is this no longer true?

Its still true. But you dont normally want to use them
simultaneously and when you do, say with an install
from the drive to a hard drive, the fact that the hard
drive has to pause occassionally while the DVD
drive head seeks isnt normally a real problem.