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My Windows 8.1 installation is horribly slow. I don't know the exact reason but I've tried EVERYTHING I could to solve its sluggishness problem, but nothing worked. Therefore I plan to reinstall a fresh copy of Windows 8.1 (I mean I want to wipe out all the present partitions and install Windows on a newly created partition). Will this cause any harm to the EFI setup? I'm asking this because there is a 128 MB partition of type "EFI Sytem Partition" on my drive. I realize that EFI is a pre-boot business. But I am not sure.

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The Extensible Firmware Interface (EFI), and its newer variant, the Unified EFI (UEFI), are firmware -- they reside on a chip on the motherboard. As such, wiping the hard disk will not damage the EFI.

That said, EFI-based computers boot by storing boot loaders on the EFI System Partition (ESP), which is a FAT32 partition on the hard disk. If you completely wipe the disk, you'll also wipe the ESP. This isn't really a problem in your scenario because, as you discovered, an EFI-based OS (including recent versions of Windows, Linux, and others) will create a fresh ESP if one doesn't already exist when you install the OS. Multiple OSes' boot loaders can reside on a single ESP, although of course that's not important if you're booting just one OS.

Another point deserves mention: EFI boot loaders can be named just about anything; they're ordinary files on the ESP. In order to know what boot loader to use, EFIs store that information in NVRAM. When you wipe a hard disk, you remove the boot loaders, but the NVRAM entries may remain behind. This shouldn't be a problem, since the EFI will either delete the entry for the (now-nonexistent) boot loader or will ignore it. When you re-install, a fresh NVRAM entry will be created. I mention this mainly because it could be relevant in some other scenarios -- for instance, if you remove the hard disk to boot some sort of emergency system, the EFI might erase your boot entry, so when you restore your hard disk, it might no longer boot. Also, some EFIs have problems managing their NVRAM entries; they sometimes disappear without cause or become corrupted, causing an inability to add new entries. The point of this is that the reliance on NVRAM is a weakness of EFI that can cause problems if you don't understand it -- or even if you do understand it but your EFI is buggy. It's just something to be aware of when you re-install an OS, set up a dual boot, or otherwise adjust the way your computer boots.

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  • Thanks a lot, Rod! I know you. I've been using rEFInd for a long time and I'm a big fan of it. In fact, if you like the idea, I'm willing to write a GUI-based rEFInd "installer", as soon as I find some spare time. That would be my token of appreciation for your great work. :)
    – Shravan
    Commented Jun 1, 2015 at 2:53
  • BTW, user453743 is me. I was just too lazy to log in using this account yesterday.
    – Shravan
    Commented Jun 1, 2015 at 2:56
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Okay, problem solved. Learnt that Windows creates a ~200 MB EFI partition automatically when installed. So, no problem.

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  • Technically as long as you have a ESP partition it will be all A OKAY ( ESP is a fallback mode for efi mostly known on MACs but is universal)
    – linuxdev2013
    Commented May 31, 2015 at 15:54

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