On 29 Jul 98 at 19:42, Louis A Pauff wrote:

>   Is there anything wrong with taking a regular IDE hard drive and
> making it the slave with an UDMA drive as the master. I have an
> extra hard drive that I was thinking about putting in my computer
> but the one that is in it now is an Ultra DMA.

  Possibly.  See below.

> Seems like I read a message on here before about this. I thought it
> said that it would cause the faster of the two drives to slow down
> to the speed of the slower drive. Or maybe that was slaving a hard
> drive with a cd rom drive, I'm not sure.

  It used to be that IDE/EIDE controllers would run each channel (two
devices) at the PIO mode of the slower device.  This had a couple of
ramifications:

1.  CD-ROM drives are much slower than hard drives, so many older
drives supported only PIO mode 1, choking almost any hard drive on
the same channel.  Newer drives support higher PIO modes to prevent
this.

2.  It appears that some newer EIDE/UDMA controllers are smart enough
to run different PIO modes to each device on a channel, also fixing
the problem.

3.  It's possible that the controllers referred to in #2 are the ones
which actually *support* UDMA[*] -- using DMA instead of PIO probably
ducks the whole issue.

[*] UDMA drives will work with an EIDE controller; the fact that it's
a UDMA drive isn't quite enough information to tell whether it's
*using* UDMA or not.

David G