What's the difference between the 2 hard drive modes of T61?

[Caladrad]

After I partition the hard drive, when I set the mode to AHCI, I can't install any OS because they can't find the hard drive. But I can install under Compatibility mode. What kind of features do they have?

Thanks

[Harryc]

AHCI Description on Wikipedia

Compatibility Mode Description on Wikipedia

[RonS]

I'd also like to add that I've benchmarked (many times) SATA drives in both SATA and Compatibility mode and I've never found any performance difference between the two modes.

[eyestrain]

Using compatibility mode may affect use of the PATA ultrabay hard drive adapter. (Item 41U3148, which doesn't seem officially supported for T6x, but does work, at least if you aren't using compatibility mode for your main drive.)

I haven't tested with a magnetic 2.5" hard drive, but with CF (compact flash) card(s) as hard drive(s) in the PATA adapter, compatibility mode can cause problems accessing the CF card(s). I don't recall if this happens even when using only one CF in the adapter, instead of both master and slave.

Maybe compatibility mode uses up an IDE drive that AHCI mode doesn't. If so, might also affect use of the extra ultrabay in the advanced dock.

[kernelpanic]

When using compatibility mode, you lose two things - hotplugging capability, and Native Command Queuing (NCQ). First, hotplugging is not an issue for the built-in boot disk in a workstation - you lose nothing by using compatibility mode. However, hotplugging is an issue for the ultrabay devices, including CD/DVD drives, and often people have problems with this. Second, NCQ affects heavily-multitasked environments only. It is meant to increase throughput on heavily used servers. You will not notice any difference in a single-user benchmark, but it has nothing to do with single-user performance. Server throughput performance can be significantly increased by NCQ, and that is also the environment where RAID/ hotplugging is critical to zero-downtime management. We dont really need these advanced mode features on our Thinkpads, as long as the ultrabay devices work in compatibility mode.