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From section §12.2.3.3 of the UEFI 2.0 spec: > Hard drives may contain multiple partitions as defined in Section 12.2.2 on partition discovery. Any partition o

From section §12.2.3.3 of the UEFI 2.0 spec: > Hard drives may contain multiple partitions as defined in Section 12.2.2 on partition discovery. Any partition on the hard drive may contain a file system that the EFI firmware recognizes. Images that are to be booted must be stored under the EFI subdirectory as defined in Sections 12.2.1 and 12.2.2. It definitely sounds like UEFI mandates support of it for internal drives (though I'm sure many implementations don't conform). Empirically I've had this work with two ESPs (one Windows 10, installed first and one Linux, installed after). I've also done this with two Linux distributions with even less fanfare. I don't know if I just got lucky that my firmware supported it and I didn't have an Windows update that tried to mess with the loader or not. I understand the difference between an ext2/3/4 /boot and FAT ESPs, thanks.

ComputerGuru 9y ago
> It definitely sounds like UEFI mandates support of it for internal drive I can see why you would interpret it that way, but the section you quoted doesn't say that. The spec for the ESP is based off of FAT32, which means that in practice, all firmwares can read any FAT32 partition. While the ESP must be FAT32 (with the different filesystem GUID), any random FAT32 partition is not an ESP. I really don't mean to overexplain this or belabor the point (forgive me if it comes across that way, but perhaps bear with me, too), but a FAT32 partition may be a boot partition without being the ESP (just as an ext4fs partition might be). The parts of the spec you quoted are not referring explicitly to an ESP, but just "any recognized partition" which also includes non-ESP FAT32 partitions. In particular, > Hard drives may contain multiple partitions as defined in Section 12.2.2 on partition discovery. I just double-checked and §12.2.2 refers to generic discovery of all partitions, not just the ESP ("This specification requires the firmware to be able to parse the legacy master boot record(MBR) (see Section 5.2.1), GUID Partition Table (GPT)(see Section 5.3.2), and El Torito (see Section 12.2.2.1) logical device volumes.") > Any partition on the hard drive may contain a file system that the EFI firmware recognizes Already addressed, but also includes support for other filesystems so that a, say, consumer electronic with a custom filesystem load its OS from said device, is not out of spec.

ComputerGuru 9y ago

> It definitely sounds like UEFI mandates support of it for internal drive I can see why you would interpret it that way, but the section you quoted doesn't say that. The spec for the ESP is based off of FAT32, which means that in practice, all firmwares can read any FAT32 partition. While the ESP must be FAT32 (with the different filesystem GUID), any random FAT32 partition is not an ESP. I really don't mean to overexplain this or belabor the point (forgive me if it comes across that way, but perhaps bear with me, too), but a FAT32 partition may be a boot partition without being the ESP (just as an ext4fs partition might be). The parts of the spec you quoted are not referring explicitly to an ESP, but just "any recognized partition" which also includes non-ESP FAT32 partitions. In particular, > Hard drives may contain multiple partitions as defined in Section 12.2.2 on partition discovery. I just double-checked and §12.2.2 refers to generic discovery of all partitions, not just the ESP ("This specification requires the firmware to be able to parse the legacy master boot record(MBR) (see Section 5.2.1), GUID Partition Table (GPT)(see Section 5.3.2), and El Torito (see Section 12.2.2.1) logical device volumes.") > Any partition on the hard drive may contain a file system that the EFI firmware recognizes Already addressed, but also includes support for other filesystems so that a, say, consumer electronic with a custom filesystem load its OS from said device, is not out of spec.