Documented MBR partitions and GUIDs
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@ -375,13 +375,15 @@ Byte Range | Value | Meaning
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446 - 509 | ========== | Partition table
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446 - 461 | part_entry | Partition table entry 1 describing ISO image size
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| | starting at LBA 0. I.e. contrary to tradition.
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| | rounded up to the next full MiB. The partition starts
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| | at LBA 0. (I.e. contrary to tradition.)
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| | See above for partition table entry format.
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| |
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462 - 509 | 0 | Unused partition entries 2 to 4
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510 - 511 | 0xaa55 | MBR signature
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---------- | ---------- | ----------------------------------------------------
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The ISO image file gets padded up to the next full MiB.
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hpa about MBR templates and partition table filesystem types:
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@ -404,6 +406,7 @@ Sources:
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http://opensource.apple.com/source/IOStorageFamily/IOStorageFamily-116/IOApplePartitionScheme.h (typedef struct Block0)
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http://www.informit.com/articles/article.aspx?p=376123&seqNum=3
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http://en.wikipedia.org/wiki/GUID_Partition_Table
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http://en.wikipedia.org/wiki/GUID
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syslinux-4.05/utils/isohybrid.c
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>>> Motivation: What systems will use the additional data ? amd64 UEFI ?
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@ -450,6 +453,8 @@ The following 32 bytes from block 0 of an Apple Partiton Map (APM) are such
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harmless code. They stem from Fedora-LiveCD.iso by Matthew Garret:
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45 52 08 00 00 00 90 90 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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It is a constant that does not depend on any properties of the ISO image or
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the information that is described in the following text.
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The layout of a Block0 of an APM is:
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@ -470,6 +475,7 @@ Byte Range | Value | Meaning (all numbers are stored big endian)
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(The block_count of 0x9090 is pure fantasy. It shall only mark the disc as
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not empty.)
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For the purpose of booting, there may be two EFI boot image files in the
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ISO image. A VFAT image and a HFS+ image. The content of both is not in the
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scope of this document.
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@ -481,6 +487,30 @@ partition entries 2 and 3, which thus claim blocks inside of partition 1.
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This partition nesting is acceptable to some EFI implementations only if the
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type of partition 1 is 0x00.
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The MBR partition entry number 1 is
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80 00 01 00 00 3f a0 89 00 00 00 00 00 50 14 00
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It marks the partition as bootable, starting at block 0, with a size that
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is the smallest full MiB not smaller than the ISO image size + 18 KiB.
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(The 18 KiB are needed for the GPT backup.)
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The ISO image has a size of 332362 blocks of 2K = 1329448 * 512 = 649.14 MiB.
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The partition size is 0x145000 = 1331200 * 512 = 650 MiB.
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Start C/H/S = 0/0/1, type is 0x0 ("Empty"), end C/H/S is 649/63/32.
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Partition 2:
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00 fe ff ff ef fe ff ff a4 00 00 00 70 04 00 00
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Start block is 0xa4 = 164 * 512 = 41 * 2048. The VFAT image file.
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Partition size is 0x0470 = 1136 * 512. The size of that file.
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Start C/H/S = 1023/254/63, type 0xef (fdisk says: "EFI (FAT-12/16/"),
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end C/H/S = 1023/254/63.
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>>> ??? why are the C/H/S values so far out ?
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Partition 3:
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00 fe ff ff 00 fe ff ff 44 05 00 00 c0 08 00 00
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Start block is 0x0544 = 1348 * 512 = 337 * 2048. The HFS+ image file.
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Partition size is 0x08c0 = 2240 * 512. The size of that file.
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Start C/H/S = 1023/254/63, type 0x00 ("Empty"), end C/H/S = 1023/254/63.
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>>> ??? why are the C/H/S values so far out ?
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The second 512-block in the ISO image is a GPT header.
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@ -501,14 +531,13 @@ Byte Range | Value | Meaning (little endian numbers, LBA unit is 512 byte)
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20 - 23 | reserved | = 0
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24 - 31 | curr_lba | Location of this header block = 0x1
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32 - 39 | back_lba | Location of header backup block = 0x144ffe = 1331198
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>>> ??? That is 437.5 2K-blocks after the image end
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>>> ??? which is at 332362 (* 4 = 1329448)
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>>> ??? 1 MiB alignment ?
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| This is 1 KiB before the end of MBR partition 1.
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>>> ??? why 1 KiB and not 512 bytes ?
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40 - 47 | first_lba | First usable LBA for partitions = 0x30 = 48
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48 - 55 | last_lba | Last usable LBA for partitions = 0x144fde = 1331166
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56 - 71 | guid | Disk GUID / UUID = {
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| | 0x73, 0x23, 0xc8, 0x79, 0x19, 0xe6, 0x97, 0x4d,
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| | 0x95, 0x17, 0x69, 0x30, 0xc5, 0x38, 0xe2, 0x99 }
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56 - 71 | guid | Disk GUID
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| | Random, produced by uuid_generate(),
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| | 32,16,16 byte swapped
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72 - 79 | part_start | Partition entries start LBA = 0x10 = 16 = byte 0x2000
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| | (This is unusual. It leaves room for the Apple
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| | partition map entries.)
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@ -525,11 +554,17 @@ chosen so that the CRC of 0 bytes of input is 0x00000000.
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The least significant bits of input bytes get processed first. I.e. bit0 of
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the last input byte gets mapped to x exp (7 + 32), bit7 of this byte gets
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mapped to x exp (0 + 32).
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The resulting division residue gets bit mirrored. E.g. bit0 becomes bit31,
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The resulting division residue gets bitwise mirrored. E.g. bit0 becomes bit31,
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bit1 becomes bit30, and so on. Further it gets exored with 0xffffffff.
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The ISO image has a size of 332362 blocks of 2K = 1329448 blocks of 512.
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A GUID consists of a 32-bit integer, two 16-bit integers, and an array of
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8 bytes. The integers are to be stored big-endian.
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A globally registered class GUID are the partition type GUIDs.
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This example uses two of them
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Basic data partition: a2 a0 d0 eb , e5 b9 , 33 44 , 87 c0 68 b6 b7 26 99 c7
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HFS+ partition : 00 53 46 48 , 00 00 , aa 11 , aa 11 00 30 65 43 ec ac
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Note that the wikipedia list shows the first 32-bit word and the next two
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16-bit words in little-endia interpretation.
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Because the block size was announced as 2048, the first Apple partition map
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@ -631,8 +666,12 @@ A GPT partion entry looks like:
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Byte Range | Value | Meaning (numbers are stored little endian)
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---------- | ---------- | ----------------------------------------------------
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0 - 15 | type_guid | Partition type guid = random
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16 - 31 | part_guid | Unique partition GUID = random
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0 - 15 | type_guid | Partition type guid = Basic data partition
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| | Wikipedia: "EBD0A0A2-B9E5-4433-87C0-68B6B72699C7"
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| | (Note: The first three words are shown byte swapped)
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16 - 31 | part_guid | Unique partition GUID
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| | Random, produced by uuid_generate()
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| | 32,16,16 byte swapped
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32 - 39 | start_lba | First LBA = 0
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40 - 47 | end_lba | Last LBA (inclusive) = 0x144828 = 1329448
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| | This is the ISO image size in blocks of 512.
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@ -659,6 +698,7 @@ Next entry is at 0x2800 = 10240:
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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Partition type GUID : "EBD0A0A2-B9E5-4433-87C0-68B6B72699C7" = Basic data
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Start at block 0xa4 = 164 * 512 = 41 * 2048. The VFAT image file.
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Last block is 0x0513 = 1299 = 164 + 1135. This end is correct.
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>>> The name is an unintentional patchwork in an 8 bit character set.
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@ -676,6 +716,7 @@ Next entry at byte 0x02100 = 8448:
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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Partition type GUID : "48465300-0000-11AA-AA11-00306543ECAC" = HFS+
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Start block is 0x0544 = 1348 * 512 = 337 * 2048. The HFS+ image file.
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Last block is 0x0e03 = 3587 = 1348 + 2239. Correct.
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>>> Frankenstein's name, again.
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@ -683,6 +724,35 @@ Last block is 0x0e03 = 3587 = 1348 + 2239. Correct.
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The rest of the System Area is 0 up to the Primary Volume Descriptor
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at block 16.
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The ISO image file gets padded up to full MiB with sufficient room for the GPT
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backup which is stored near the very end of the image file. There is need for
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at least 16.5 KiB, which effectively occupy 18 KiB.
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The backup partition array is stored 17 KiB before the end of MBR partition 1
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resp. the image file.
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>>> why not 16.5 KiB before end ? Wikipedia suggests "LBA -33" counted from end.
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The content of the partition arry is the same as the one of the primary array
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at byte 0x4000.
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The GPT header is stored 1 KiB before the end of MBR partition 1.
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>>> why not 512 byte before end ? Wikipedia suggests "LBA -1" counted from end.
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45 46 49 20 50 41 52 54 00 00 01 00 5c 00 00 00
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E F I P A R T
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f6 61 10 1c 00 00 00 00 fe 4f 14 00 00 00 00 00
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01 00 00 00 00 00 00 00 30 00 00 00 00 00 00 00
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de 4f 14 00 00 00 00 00 73 23 c8 79 19 e6 97 4d
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95 17 69 30 c5 38 e2 99 de 4f 14 00 00 00 00 00
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80 00 00 00 80 00 00 00 5b 6b 8a 65
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It differs by its own CRC and by some of its parameters:
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Own address is 0x144ffe. The backup lba is 0x01 = Primary GPT header.
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Partition entries start is 0x144fde
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>>> This overlaps with the last usable LBA. The backup GPT must move up by
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>>> 512 bytes.
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------------------------------------------------------------------------------
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