Difference between ATA and AHCI setting for SATA operation in BIOS

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Difference between ATA and AHCI setting for SATA operation in BIOS

  • I just got my new 1720 Inspiron, and I had a problem when trying to create an image of the C and D drive using the Ultimate Boot CD (BART), it would never see my hard disk partitions.  I changed the BIOS setting for the On Board Devices from AHCI (default) to ATA for SATA operation.  I also had to change the Flash Cache Module to be disabled, it was enabled in the Factory Default.  The result of these changes was good, I was able to see my C and D drive when booting from my Ultimate Boot CD.  I was wondering does anyone know what these changes do?  Should I leave my BIOS at the new setting, or will I lose performance from my hard disk?
  • 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
  • Thanks for the excellant explanation, very much appreciated.
  • gmjohnson99,
     
    The Flash Cache Modules will only be included with the system if the unit shipped with Microsoft Vista and the "Hybrid Hard Drive" option was selected at the time of purchase. The BIOS setting for this device is set to "Enabled" by default, this doesn't indicate that the unit has the module.
     
    Basically, the FCM is designed to be used in tandem with an AHCI enabled SATA HDD to retrieve frequently accessed data from the FCM instead of having to go back to the hard drive, which saves time and battery power.
     
    Mike