This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
(This section assumes you're using a PC.)
You generally want the hard drives and CD-ROM drives on different channels,
or CD-ROM accesses can interfere with hard drive accesses. Most older
devices can't share the ATA bus, so only one device can be active at a time.
For example, suppose you have a hard drive as master and a CD recorder as
slave on the same channel. If you issue a command to write some blocks
to the CD recorder, the system can't read anything from the hard drive
until the CD write request completes. As long as the system is fast
enough, and can read enough data between writes to keep the CD recorder's
buffer full, this doesn't create any problems.
If you put the hard drive and the CD recorder on different channels,
the commands are allowed to overlap. In practice, on Win9x systems this
doesn't make much of a difference, because Win9x won't usually access
more than one IDE device at a time. On systems like OS/2 and Linux,
the difference is more significant.
Proposals for command overlap (sending commands to multiple devices
simultaneously) and command queueing (sending several commands to the
same device all at once) were introduced as optional features during the
development of the ATA-3 specification. They're part of ATA/ATAPI 4.
For command overlap to be effective, both devices on the channel must
support the feature. If the hard drive does but the CD recorder doesn't,
you won't get much benefit.
If you're not sure that your CD recorder has an ATAPI-4 interface, you
probably ought to put it on a separate channel from the hard drive.
For information related to this topic, see "Does an old HD or CDROM
slow down a new drive?", in section 5.3 of the IDE/Fast-ATA FAQ at
The recommended configuration looks like this:
master: first hard drive
slave: (optional) second hard drive
master: CD-ROM drive
slave: CD-R/CD-RW drive
It doesn't seem to matter whether the CD-ROM or CD recorder is the master.
If you use the CD recorder as your only CD-ROM drive, make it the master.
Having the CD-ROM drive and the CD recorder on the same channel doesn't
necessarily prevent CD-to-CD copying, but you're still better off writing
from the hard drive. At high speeds, the CPU utilization for CD-ROM drives
without DMA enabled can be very high.
Keep the cables as short as you can. Sometimes the longer (60cm) cables
will work fine with one drive but start having integrity problems when two
devices are attached.
NOTE: early versions of the Intel PIIX Bus Mastering IDE driver may
interfere with the ability to use a CD recorder. The typical symptom
is a system hang when writing or test-writing to a disc. The latest
version of the Intel driver (which includes an uninstaller) can be
found at http://developer.intel.com/design/chipsets/drivers/busmastr/.
The Adaptec page http://www.adaptec.com/support/configuration/cdrecide.html
also describes the problem.
NOTE: early versions of the VIA Bus Mastering IDE drivers were similarly
afflicted. See http://www.via.com.tw/support/faq.htm.
Win95/Win98 users can resolve the bus-mastering IDE driver problems by
installing Win98 Second Edition (a/k/a Win98SE) after removing any
manufacturer-supplied bus-mastering drivers.
The ASPI (Advanced SCSI Programmer's Interface) layer is used during CD
recording, even for IDE recorders. See section (4-44) for information on
how to make sure you have what you need. The original Win95A/B WinASPI
may have problems with IDE recorders.