SATA ports can have 3 settings (modes): IDE, AHCI, & RAID.
Optical drives (CD, DVD, Blu-ray, etc.) normally use IDE mode.
Older HDDs normally use IDE mode. Current generation HDDs have slightly better performance in AHCI mode.
SSDs need to be in AHCI mode. They will work in IDE mode, but at reduced performance.
If you are combining multiple HDDs or multiple SSDs into a RAID array then the drives being used in the array have to be in RAID mode.
What's a RAID array? Thank's all for the answers so far
I am thinking of changing to SSD for main drive, and HDD for storage, would they need to be in RAID...or ACHI?