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On Monday, 14 December 2020 05:41:46 GMT Thomas Mueller wrote: |
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> Excerpt from Michael: |
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> > Right, on UEFI MoBos the ESP partition used by the UEFI firmware to locate |
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> > and run *.EFI executables must be FAT32. Such .EFI executables stored on |
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> > the ESP may be OS boot managers/loaders, or other UEFI compatible |
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> > applications. The boot manager loaded by UEFI is then left to its own |
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> > mechanisms (boot loader and fs drivers) to load whatever fs the kernel |
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> > image resides on. |
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> |
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> Is it necessary for the ESP to be FAT32, as opposed to FAT16 or FAT12? |
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Looking again at the UEFI firmware specification it states "... encompasses |
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FAT32 for a system partition, and FAT12 or FAT16 for removable media" and that |
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the "variant of EFI FAT to use is defined by the size of the media". |
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So, there is no *must use FAT32* as such in the specification, although it can |
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be inferred from the way it is written that a system partition, defined as "a |
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contiguous grouping of sectors on the disk", will use FAT32. On removable |
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devices (diskettes) the partition is defined to be the entire media and space |
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limitations apply. Other removable devices may have more space and a call |
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will be made accordingly. I suppose if you have an ESP no larger than 16 MiB |
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(4K clusters) and you can fit all your boot manager/OS loader files in there, |
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you would use FAT12. |
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> What happens if the ESP is formatted FAT12 or FAT16? |
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I expect it would/should be read by the UEFI firmware and is suitable for |
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space limited systems. Most PC installations have GBs of space on their |
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disks, so avoiding FAT32 wouldn't make much sense. |
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> In some cases, ESP might be small enough that FAT32 would not be |
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> appropriate, especially when there is only one OS installation on the disk. |
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> |
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> That would be the case on many MS-Windows or Mac computers, and also other |
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> OSes when installed on a USB stick. |
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> |
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> Tom |
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Right, but a USB stick is probably considered "removable media" and its space |
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could be deemed as limited. |
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I loosely recall AppleMac boot partitions being ~200MB and MSWindows ~300MB, |
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but don't have a machine to hand to check right now. For most use cases even |
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with multiple OSs installed, that's probably enough space to fit FAT32. |
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