IDE/ATA Configuration and Cabling

Based on the IDE/ATA configuration performance factors outlined in this section, I have identified what I think are sensible configuration options for setting up IDE channels for different hard disk and ATAPI device combinations. These recommendations are oriented towards maximizing overall system performance, and are based primarily on my experience and understanding of the IDE/ATA interface and the way most people use their systems.

The following is a list of assumptions and notes regarding these recommended configurations:

Systems vary more today in terms of how many IDE/ATA channels they have, and of what type, than ever before. I cannot list every possible configuration, and I certainly am not going to bother with the ones that obviously make no sense.
The best setup depends to a great extent on the needs of the individual, so use the recommendations on this page as guidelines only. Do what works for you.
If at all possible, the best configuration is always to have each device on a separate channel. Of course, not all channels are created equal. Hard disks and faster ATAPI devices should always be on a channel connected to the PCI bus (or VLB for 486-class systems). Older or slower ATAPI devices like slower CD-ROMs or tape drives can be connected to an ISA-bus tertiary channel such as the one on a sound card, though this is still usually not optimal.
I am assuming that the channels on the motherboard, and any channels on an add-in controller, have the same support for transfer modes and hard disk size. If an add-in card is installed in an older system to provide support for faster transfer modes not supported by the integrated controllers, or to get around a hard disk size barrier, then newer, larger drives should be connected to those channels, and the built in controllers used for older devices. Note that booting from a drive connected to an add-in card may require a change to the BIOS boot sequence setting. See here for more.
Some people are most concerned with absolute performance, and are willing to use extra controllers to get it, even if it costs them extra IRQs. Other people don't have IRQs to burn and may not even want to use the secondary IDE controller. I assume that most people will not disable the secondary IDE/ATA channel just to save an IRQ, though this is an option if you have only two devices.
Finally, remember that choosing an ideal drive configuration is really an optimization; in most cases the differences between various alternatives are not enormous.

These are my recommendations for the more common mixtures of up to five hard disks and/or ATAPI (optical, tape, removable storage) drives:

Hard Disks	ATAPI Devices	Notes
1	0	This is fairly uncommon today, since almost all systems have at least one optical drive. The best configuration is to use the primary master for the hard disk and disable the secondary controller (to save one IRQ).
1	1	The most common default configuration. Unless system resources are very tight, put the hard disk as a single drive on the master channel, and the ATAPI drive on the secondary channel.
2	1	The best configuration is to put each device on a separate channel through the use of a third IDE/ATA channel. If only two channels are available, it is generally best to put the fastest drive as a single device on the primary channel, the second hard disk as the master on the secondary channel, and the ATAPI as the slave on the secondary.
1	2	This is a common configuration when a second ATAPI device is added to a new system; the best configuration depends on what that device is. In general, put the hard disk by itself and share the secondary channel between the two ATAPI drives. However, if your two drives are a CD-ROM and a CD-RW drive, and you are doing a lot of copying from the CD-ROM drive to the CD-RW, you may have better luck separating those devices onto separate channels.
2	2	For optimal performance, buy an add-in controller card and use all four channels for the four devices. If you have three channels, then put the boot drive by itself on the primary channel, and then split the remaining three devices on the secondary and tertiary channels as described in the row just above. If you have only two channels, there are several options. I would put the fastest drive as the boot device on the primary master, and whatever drive is the least used as the slave on that channel. Then put the other two devices on the secondary channel. Avoid putting drives that can't be run in Ultra DMA with the boot device.
3	1	Fairly similar configuration to the two rows above. Use four channels if possible. If there are three put the two slowest devices together. If there are only two channels, configure as for the 2+2 option above.
1	3	Same as for 3+1 just above.
3	2	If you have more than four devices, you will need to add a controller to get a third IDE/ATA channel--or get rid of one of your devices. ;^) The best option is to add a PCI-based IDE/ATA controller card, which will give you four channels. If this is the case, put the three fastest or more used devices on their own channels, and the two slowest devices together. If you have three channels, put the boot drive by itself and split the other four drives up over the remaining two channels as described in the discussion for the 2+2 case.
2	3	Same as for 3+2 just above.

Next: Small Computer Systems Interface (SCSI)

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