Question Regarding AHCI and Legacy BIOS

Discussion in 'Windows 7' started by alexz721, Jun 20, 2014.

  1. alexz721

    alexz721 MDL Novice

    May 15, 2011
    Hi all, really appreciate what you do here.

    My question is relating to installing Windows 7 on an SSD. I've read a lot about the differences between the UEFI and legacy BIOS but haven't found an answer to this question. I know that UEFI mode formats a drive in GPT and legacy BIOS mode does it in MBR. My question is, can I enable AHCI for an SSD in legacy BIOS mode using an MBR boot sector? I assume I can, but I would like to make sure. Using an Asrock mobo.

    My second question is if I install Windows 7 this way, if I for example have a 4TB external drive, can I utilize it's full capacity if it's formatted in GPT, or does the boot drive also have to be GPT?

    Thank you.
  2. Mr.X

    Mr.X MDL Guru

    Jul 14, 2013
    1. Yes, you can enable it.
    2. No, boot drive hasn't to be GPT although the external drive should be.
  3. tnx

    tnx MDL Expert

    Sep 2, 2008
    What mobo is it ?

    Has it got SATA 6mb p/s

    A solid drive would be 6mb p/s so would not perform at it's best on an older SATA port.would still be a little faster than a mechanical 3mb p/s drive.

    UEFI does not format a drive into MBR or GPT, you choose that via disk management.
    You would need that size of drive to be GPT.
    Whether a OS on MBR can utilise a large drive on GPT or the OS has to be on GPT also I dont know.
    But I'm sure somebody on here will do.

    Then dont forget Daz's loader does not work on GPT drives. Does this board hold SLIC2.1 ?

    1 post ever three years. Keep it up ;)
  4. alexz721

    alexz721 MDL Novice

    May 15, 2011
    Thanks guys! I'll post back if I encounter any problems.
  5. shx

    shx MDL Novice

    Jun 20, 2014
    Windows needs MBR for legacy BIOS and GPT for (U)EFI on it's boot disk. Any other combinations will fail.
    For non-boot disks, Windows takes all combinations - however, keep in mind, that MBR cannot use more than 2TB on a individual disk (so on a MBR formatted 4TB, only 2TB are usable) - GPT for your external 4TB disk is therefore strongly encouraged. GPT is the better and newer partition table anyways.
    AHCI is supported natively by all Windows OSes since Vista (XP needs additional drivers for SATA anyways), and all somewhat modern Linux kernels. Unless you believe in IRRT (Intel Rapid Restore Technology - claims to perform hibernation faster), AHCI is the single best option for SATA drives (no supported OS needs PATA/IDE compatibility these days - even DOS based rescue disks learned how SATA/AHCI works).