In my BIOS there is an option of using Native IDE or AHCI, which is prefered when installing an older OS like Windows 7 (x64)?
Only use IDE mode on legacy operating systems like windows 98. From windows 2000 and up, you should install windows in AHCI for better performance (windows 2000 and XP require additional drivers, vista and newer works out of the box)
Not only is their IDE and AHCI but the new kid on the block is called NVMe NVMe does not have the 6gbs limit like the AHCI Sata does.
The SSD memory controllers have there limits to. The latest 3D NAND based SSD´s have dual channel memory controllers to archive greater speeds.
Sata (AHCI) maxes out at up to 6gb, no matter if the ssd can go faster or not, Sata ssd's can exceed 6gbs. The AHCI standard was never intended to reach or exceed 6gbs with platter drives, and AHCI was designed for platter drives and SSD's did not exist when AHCI came out. It's the reason that they came out with NVMe drives NVMe has a speed of up to 32gb
From Vista up HDDs will profit from using AHCI due to NCQ (Native Command Queuing), this will massively improve parallel write and read processes.
only if the HDDs are SATA-2 (Sata 3G) based or greater will benefit with AHCI 1st gen SATA (aka SATA-1 or Sata 1.5g), no benefit with AHCI
I have a HDD (not SSD) and it's formatted in MBR to make Windows 7 easier to install, is AHCI still recommended with these things?