installation - Install Windows 7 Ultimate x64 as UEFI with GPT

28
2014-03
  • Vishnu Y

    I bought a Samsung laptop (Model: NP350V5C-S0BIN) which came preinstalled with Windows 8. I dont like Windows 8 and want to install Windows 7. I have disabled FAST BOOT and SECURE BOOT.

    My questions are.

    1) On disabling Secure Boot, I found three OS Selection Modes namely, "UEFI", "CSM OS" and "UEFI or Legacy OS". Which one should I choose to install Windows 7 x64 and Why? (Really confused as in some forum they are telling to use UEFI while few other forus telling "UEFI or Legacy OS")

    2) I converted the GPT to MBR once I tried to install windows 7 unknowingly but the installation failed. So if I select UEFI DVD Drive to install, will it automatically convert MBR back to GPT upon creating partitions?

    Please provide the sufficient help.

    • Answers
  • Rod Smith

    "CSM" and "legacy" are synonymous in this context, so -10 points for clarity to whoever wrote your firmware's user interface. Since you want to install in EFI mode, the "UEFI" option makes the most sense; if the names are truly descriptive of their effects, this will force the computer to boot in EFI mode, which is what you want. The "UEFI or Legacy OS" option might also work, but is more hit-or-miss -- there's really no way to know in which mode the Windows installer will boot. If it boots in EFI/UEFI mode, then the effect will be identical to using the "UEFI" option; but if it boots in BIOS/CSM/legacy mode, you'll be wasting your time. You should definitely avoid the "Legacy" option. A caveat: Many firmware interface options are very poorly named, so you may find that these options don't have the effects that they seem to describe.

    I don't know offhand what the Windows installer does when confronted with an MBR disk during an EFI-mode installation. It might work fine, particularly if the disk has no partitions; but if you want to be 100% certain that you're installing in EFI mode, you might want to pre-partition the disk using GPT. Personally, I'd use a Linux live CD for this, like Parted Magic or System Rescue CD; but if you're not comfortable with Linux, you may prefer to use a Windows emergency disc and Windows tools. Either way, ensure that the disk uses GPT and the Windows installer can take care of the rest.


    • Related Question

    How to install Windows 7 x64 on GPT?
  • Dani

    How can I install Windows 7 x64 on GUID partition table? My motherboard has UEFI. I tried using Ubuntu to create the GPT and NTFS partition on it, but Windows 7 just says

    Windows cannot be installed to this disk. The selected disk is of the GPT partition style

    I found this: Use the Diskpart.efi Utility to Create a GUID Partition Table Partition on a Raw Disk in Windows – but all diskpart commands in it don't work, it seems its a different version of diskpart.

    How can I make this work?


    • Related Answers
  • JdeBP

    Microsoft erroneously conflates has an EFI partitioned hard disc with has EFI firmware. This is, of course, clearly wrong. It's quite possible — and indeed is becoming ever more desirable these days — to have an EFI partitioned disc on a machine that has old non-EFI firmware.

    Moreover, as of revision 2.3.1 of the UEFI Specification, the EFI partition table has a "startable" attribute defined for partitions and it is possible to even bootstrap from EFI partitioned discs on a machine that has old non-EFI firmware. Old-style PC98 MBR bootstrap programs can look for partitions marked with the "startable" attribute in the EFI partition table and bootstrap the flagged partition's Volume Boot Record bootstrap program in the old PC98 way.

    There are only two sources of such EFI-partitioning-aware MBR bootstrap programs right now:

    • I've written and published one.
    • The so-called "GPT" MBR boostrap in SYSLINUX, written by H. Peter Anvin, is another.

    One of the several consequences of Microsoft's error is that if the Windows NT 6.1 install disc is bootstrapped in the old PC98 way, as you've done, the Windows NT 6.1 installer will think that there's old PC98 firmware, and so declare that it cannot be installed to EFI partitioned hard discs. The Windows NT 6.1 installer has to be invoked from an install medium that has in turn been bootstrapped from new EFI firmware, in order for it to accept the idea of installing Windows NT 6.1 to a disc partitioned with the new EFI partitioning scheme.

    As the Microsoft documentation explains, the installation CD-ROM is in fact dual-boot. A machine with old PC98 firmware will bootstrap one operating system image and installation program; and a machine with new EFI firmware will bootstrap another. A machine with a compatibility support module can bootstrap an installation medium either way. One has to instruct one's firmware to bootstrap the installation CD-ROM in the right way, the new EFI way.

    As Rod Smith explains, one can also, alternatively, manually construct a non-dual-boot Windows NT 6.1 install disc that only bootstraps in the new EFI way.

    Further reading