OpenStandards

OpenUPT

Open Unmanaged Partition Table is a format that allows for partitioning and booting of unmanaged disks.

Sector Layout

Sectors in an OpenUPT-formatted drive should be laid out and used for the following purposes:

Sector 1: The boot sector. This contains up to 512 bytes of Lua code that will be executed upon booting this disk. If a disk is not meant to be booted, the code contained in this sector should just be a stub that prints an error, such as “Non bootable disk. Press any key to reboot.”

Sectors 2-24: These sectors are reserved for use by the bootloader. Usually, these sectors contain executable code for the boot sector to run. If there isn’t a bootloader installed, or these sectors aren’t needed, they should be left blank.

Sector 25: The partition table. This sector contains 8 64-byte entries describing partitions on this drive. The details of this are in the “Partition Table” section.

Sectors 26-32: Reserved for future use.

Sectors 33-end of disk: The actual data on the disk.

Partition Table

The partition table is 512 bytes (1 sector) in size, and holds 8 64-byte entries. This means there can be a maximum of 8 partitions on one drive. An entry in the table has this format: (Note: all data is little-endian!)

struct ptentry {
  // Bytes 1-4: Start sector, 32-bit unsigned integer
  unsigned int start_sector;

  // Bytes 5-8: End sector, 32-bit unsigned integer
  unsigned int end_sector;

  // Bytes 9-16: FS type, 8 character string
  char fstype[8];

  // Bytes 17-20: Partition flags, 4 bytes
  unsigned int flags;

  // Bytes 21-28: Partition GUID, 8 randomly-generated bytes
  char uuid[8];

  // Bytes 29-64: Partition label, 36 character string
  char label[36];
}