[Bug 811485] Re: EFI SYSTEM PARTITION should be atleast 100 MiB size and formatted as FAT32, not FAT16

[Roderick Smith]

Adam, you've misread my comment about Windows and MBR. Allow me to
rephrase: When booted in BIOS mode, Windows will only install to or boot
from an MBR partition table (normally without a GPT, although Windows
treats hybrid MBR disks as MBR disks); and when booted in EFI mode,
Windows will only install to or boot from a GPT disk (WITHOUT any MBR
entries except for the type-0xEE protective entry). Thus, if a disk has
an MBR with non-0xEE partitions defined, as Allen reported, and if it's
successfully booting Windows, then it follows logically that Windows is
booting in BIOS mode on that computer, not in EFI mode, since Windows
will not boot in EFI mode from an MBR disk (AFAIK).

You are correct that the GPT spec requires a protective MBR; however,
when I refer to an "MBR partition table," I mean a real MBR partition
table with actual defined partitions, NOT merely a protective MBR, which
is just a dummy data structure intended to keep GPT-unaware utilities
and OSes from messing with the disk.

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https://bugs.launchpad.net/bugs/811485

Title:
  EFI SYSTEM PARTITION should be atleast 100 MiB size and formatted as
  FAT32, not FAT16

Status in “partman-efi” package in Ubuntu:
  Confirmed

Bug description:
  Create a EFI SYSTEM PARTITION of minimum 100 MiB size (200 MiB
  recomended). Also partman-efi should use FAT32 instead of FAT16 for
  EFI SYSTEM PARTITION as mandated by the UEFI 2.3.1 Spec. FAT16 ESP
  partition is not recognised by Windows 7 UEFI bootloader because of
  this.

  The below quote is copied form the UEFI Specification 2.3.1 - Chapter
  12.3 File System Format.

  [QUOTE]
  EFI encompasses the use of FAT32 for a system partition, and FAT12 or FAT16 for removable media. The FAT32 system partition is identified by an OSType value other than that used to identify previous versions of FAT. This unique partition type distinguishes an EFI defined file system from a normal FAT file system. The file system supported by EFI includes support for long file names.

  FAT defines that all files in a directory must have a unique name, and
  unique is defined as a case insensitive match.

  UEFI does not impose a restriction on the number or location of System Partitions that can exist on a system. System Partitions are discovered when required by UEFI firmware by examining the partition GUID and verifying that the contents of the partition conform to the FAT file system as defined in Section 12.3.1.1. Further, UEFI implementations may allow the use of conforming FAT partitions which do not use the ESP GUID. Partition creators may prevent UEFI firmware from examining and using a specific partition by setting bit 1 of the Partition Attributes (see 5.3.3) which will exclude the partition as a potential ESP.
  [/QUOTE]

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