Gigabyte m/bs has BIOS Rescue embedded in bios and Xpress Recovery embedded in driver CD features. Bios Rescue feature will occupy size around 2MB in your HDD. This space occupied by this feature cannot be recovered. Xpress Recovery feature will occupy around 6MB in your HDD when using Gigabyte driver CD to boot, This space occupied by this feature cannot be recovered. This feature will occupy more space further once you choose to backup the existing data of your HDD. The space depends on the size of your data store in your HDD, ratio around 1 to 1. The space occupied by this feature can be used as a separate partition after deleting the backup data.
AHCI is a programming interface for SATA host controller. It provides new features, such as NCQ and hot plug, to increase performance. If you want to enable AHCI, please kindly set "SATAAHCI Mode" as AHCI in the BIOS. Then, install GIGABYTE SATA2 RAID driver in Windows XP/2000 O.S.