One method of tuning involves adjusting the settings in your BIOS. Because the BIOS is not Linux and every BIOS seems different, always read your motherboard manual for better possible settings and make certain that all the drives are detected correctly by the BIOS. Change only one setting at a time.
Linux does provide a limited means to interact with BIOS settings during the boot process (mostly overriding them). In this section, you will learn about those commands.
Other options are in the following list, and are more fully outlined in the BOOTPROMPT HOWTO and the kernel documentation. These commands can be used to force the IDE controllers and drives to be optimally configured. Of course, YMMV (Your Mileage May Vary) because these do not work for everyone.
idex=dma—This will force DMA support to be turned on for the primary IDE bus, where x=0, or the secondary bus, where x=1.
idex=autotune—This command will attempt to tune the interface for optimal performance.
hdx=ide-scsi—This command will enable SCSI emulation of an IDE drive. This is required for some CD-RW drives to work properly in write mode and it might provide some performance improvements for regular CD-R drives as well.
idebus=xx—This can be any number from 20 to 66; autodetection is attempted, but this can set it manually if dmesg says that it isn’t autodetected correctly or if you have it set in the BIOS to a different value (overclocked). Most PCI controllers will be happy with 33.
pci=biosirq—Some motherboards might cause Linux to generate an error message saying that you should use this. Look in dmesg for it; if you do not see it, you don’t need to use it.
These options can be entered into /etc/lilo.conf or /boot/grub/grub.conf in the same way as other options are appended.
Source of Information : Sams Ubuntu Unleashed 2008 Edition
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