On 23 Feb 98 at 0:34, Steve Snyder wrote:

>    Another thought popped up after talking with a tech yesterday.
> He mentioned that 2 HDs of different transfer speeds? will
> only work at the speed of the slower drive.  He told me to
> check the "Mode" of the drives as the system booted up.
> My 3 year old Western Digital comes up as "Mode 3" while the
> system is booting.  And the recently returned Seagate came up
> as "Mode 4".  Would this possibly cause any problems, including
> what I recently experienced?

  Each IDE/EIDE mode ("PIO mode") has a maximum transfer rate, but
few drives currently made will meet that speed for more than
occasional bursts.  Sustained rates tend to be closer to half the
maximums.
  Traditionally, IDE/EIDE has been forced to run each channel (1 or
two devices) at the highest PIO mode supported by both devices -- in
your case above, that will be mode 3.[*]  Note that since the sustained
throughput of a mode 4 drive is likely to be in the mode 3 range,
you're not necessarily losing speed most of the time, just using up
more of your available EIDE bandwidth.
  The "traditional" case has to do with CD-ROM drives, which can be
about 10x slower than hard drives.  Many early IDE/ATAPI CD-ROM
drives only bothered to support PIO mode 1, so putting one on the
same channel with your mode 4 Seagate *would* slow it down noticably.

[*] I've run into a few references/mentions which seem to suggest
that recent EIDE controllers -- possibly any which support UDMA? --
may be able to run devices on a single channel in different modes.  I
haven't found clear details yet, though.

David G