If you set the SATA mode to IDE in the bios,linux will load IDE driver for the hard disk,and your SATA hard diskl will got a low speed,about 5M/S.You can solve the issue by change the SATA mode to AHCI before you install the linux OS,if you change the mode after you install the linux OS ,the linux OS which you installed will can't find the disk.You can modify /boot/grub/grub.conf (add 'all-generic-ide pci-nommconf' at the end of the 'kernel' line)for example:
title CentOS (2.6.18-194.el5)
root (hd0,0)
kernel /vmlinuz-2.6.18-194.el5 ro root=/dev/VolGroup00/LogVol00 all-generic-ide pci-nommconf
initrd /initrd-2.6.18-194.el5.img
Also you can add 'linux all-generic-ide pci-nommconf' or 'linux text all-generic-ide pci-nommconf' when you install the linux OS.
You can check your harddisk speed by command 'hdparm -t /dev/hda',you should change the 'hda' according to your OS!
