Basically AHCI is a newer way to interface with the SATA controller. This allows you to take advantage of SATA features such as Native Command Queuing (basically, you give your hard drive a bunch of commands, and let it figure out the best order to run them in to increase total throughput... without command queuing, the operating system can only send one command at a time, and the OS really has very little idea how to do this in the optimum order... this helps most when you are accessing data scattered over the drive rather than in order... if you run multiple programs that both use the disk it'll help, but it will have little effect when playing a movie off the hard drive), there are some other features that are enabled, but are more appropriate for desktops. The downside is you need updated drivers (which are apparently not on the BART cd).
In ATA mode, the SATA controller is basically pretending to be Intel's last generation parallel ATA controller. Weather or not you have real performance differences between the two modes probably depends on exactly how you use your disk drive, so you may want to try it out (if your Operating System doesn't get spooked by the change). Additionally, you should be happy you have the option, I have a Latitude D520, which doesn't have this option, and I'm stuck in ATA mode, when command queuing could really help me out.
I don't know what the Flash Cache module does.
[edited to form paragraphs]
Message Edited by toast0 on 09-03-2007 12:04 AM