See IDE disk settings (must be root)

hdparm /dev/hd? (hda, hdb, etc.)

Set DMA for IDE disks (must be root)

hdparm -d1 /dev/hd? (hda, hdb, etc.)
Usually big performance gains, especially for DVD drives.

Tune additional IDE disk settings (must be root)

hdparm -d1 -c3 -m16 /dev/hd? (hda, hdb, etc.)
The -c3 option turns on the 32-bit EIDE interface. The -m16 option sets the read ahead buffer to 16 sectors. Fairly non-agressive settings for modern EIDE disk.

More aggressive IDE disk settings (must be root)

hdparm -d1 -c1 -m16 /dev/hd? (hda, hdb, etc.)
The -c1 option has less overhead than -c3 but works with fewer chipsets. Newer drives should work fine with -c1.

Aggressive IDE disk settings with multiple disks (must be root)

hdparm -d1 -c1 -m16 -u1 /dev/hd? (hda, hdb, etc.)
The -u1 option permits the driver to unmask other interrupts during a disk interrupt. With multiple drives/controllers, this can dramatically increase performance. However, quoting the man page, some drive/controller combinations do not tolerate the increased I/O latencies possible when this feature is enabled, resulting in massive filesystem corruption. Use with extreme caution.

Test IDE disk performance (must be root)

hdparm -tT /dev/hd? (hda, hdb, etc.)