More boot sector README updates
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Jeff Parsons
Jeff Parsons
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commit
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3 changed files with 203 additions and 109 deletions
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@ -78,6 +78,41 @@ CHKDSK reports:
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### PC-DOS 1.00 Boot Sector
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The boot sector of the PC-DOS 1.00 disk image contains the following bytes:
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00000000 eb 2f 14 00 00 00 60 00 20 37 2d 4d 61 79 2d 38 |./....`. 7-May-8|
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00000010 31 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |1...............|
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00000020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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00000030 00 fa 8c c8 8e d8 ba 00 00 8e d2 bc 00 7c fb a1 |.............|..|
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00000040 06 7c 8e d8 8e c0 ba 00 00 8b c2 cd 13 72 41 e8 |.|...........rA.|
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00000050 58 00 72 fb 2e 8b 0e 02 7c 51 bb 00 00 33 d2 b9 |X.r.....|Q...3..|
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00000060 08 00 be 01 00 56 b0 01 b4 02 cd 13 72 22 5e 58 |.....V......r"^X|
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00000070 e8 e7 00 2b c6 74 14 fe c5 b1 01 be 08 00 3b c6 |...+.t........;.|
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00000080 73 04 8b f0 eb 01 96 56 50 eb dd 2e ff 2e 04 7c |s......VP......||
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00000090 be 44 7d b8 42 7d 50 32 ff ac 24 7f 74 0b 56 b4 |.D}.B}P2..$.t.V.|
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000000a0 0e bb 07 00 cd 10 5e eb f0 c3 bb 00 00 b9 04 00 |......^.........|
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000000b0 b8 01 02 cd 13 1e 72 34 8c c8 8e d8 bf 00 00 b9 |......r4........|
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000000c0 0b 00 26 80 0d 20 26 80 8d 20 00 20 47 e2 f3 bf |..&.. &.. . G...|
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000000d0 00 00 be 76 7d b9 0b 00 fc f3 a6 75 0f bf 20 00 |...v}......u.. .|
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000000e0 be 82 7d b9 0b 00 f3 a6 75 02 1f c3 be f9 7c e8 |..}.....u.....|.|
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000000f0 a5 ff b4 00 cd 16 1f f9 c3 0d 0a 4e 6f 6e 2d 53 |...........Non-S|
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00000100 79 73 74 65 6d 20 64 69 73 6b 20 6f 72 20 64 69 |ystem disk or di|
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00000110 73 6b 20 65 72 72 6f f2 0d 0a 52 65 70 6c 61 63 |sk erro...Replac|
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00000120 65 20 61 6e 64 20 73 74 72 69 6b 65 20 61 6e 79 |e and strike any|
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00000130 20 6b 65 79 20 77 68 65 6e 20 72 65 61 64 f9 0d | key when read..|
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00000140 0a 00 cd 18 0d 0a 44 69 73 6b 20 42 6f 6f 74 20 |......Disk Boot |
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00000150 66 61 69 6c 75 72 e5 0d 0a 00 50 52 8b c6 bf 00 |failur....PR....|
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00000160 02 f7 e7 03 d8 5a 58 c3 52 6f 62 65 72 74 20 4f |.....ZX.Robert O|
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00000170 27 52 65 61 72 20 69 62 6d 62 69 6f 20 20 63 6f |'Rear ibmbio co|
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00000180 6d b0 69 62 6d 64 6f 73 20 20 63 6f 6d b0 c9 00 |m.ibmdos com...|
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00000190 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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A number of people have already delved into the guts of the PC-DOS 1.00 boot sector, including:
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* [Reverse-Engineering DOS 1.0 – Part 1: The Boot Sector (May 7, 2009 by Michael Steil)](http://www.pagetable.com/?p=165)
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@ -265,46 +300,43 @@ Using the PCjs Debugger, we can examine the boot sector in its native environmen
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&0000:7C00 EB2F JMP 7C31
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>> db 7c00 l200
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&7C00 EB 2F 14 00 00 00 60 00-20 37 2D 4D 61 79 2D 38 ./....`. 7-May-8
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&7C10 31 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 1...............
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&7C20 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&7C30 00 FA 8C C8 8E D8 BA 00-00 8E D2 BC 00 7C FB A1 .............|..
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&7C40 06 7C 8E D8 8E C0 BA 00-00 8B C2 CD 13 72 41 E8 .|...........rA.
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&7C50 58 00 72 FB 2E 8B 0E 02-7C 51 BB 00 00 33 D2 B9 X.r.....|Q...3..
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&7C60 08 00 BE 01 00 56 B0 01-B4 02 CD 13 72 22 5E 58 .....V......r"^X
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&7C70 E8 E7 00 2B C6 74 14 FE-C5 B1 01 BE 08 00 3B C6 ...+.t........;.
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&7C80 73 04 8B F0 EB 01 96 56-50 EB DD 2E FF 2E 04 7C s......VP......|
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&7C90 BE 44 7D B8 42 7D 50 32-FF AC 24 7F 74 0B 56 B4 .D}.B}P2..$t.V.
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&7CA0 0E BB 07 00 CD 10 5E EB-F0 C3 BB 00 00 B9 04 00 ......^.........
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&7CB0 B8 01 02 CD 13 1E 72 34-8C C8 8E D8 BF 00 00 B9 ......r4........
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&7CC0 0B 00 26 80 0D 20 26 80-8D 20 00 20 47 E2 F3 BF ..&.. &.. . G...
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&7CD0 00 00 BE 76 7D B9 0B 00-FC F3 A6 75 0F BF 20 00 ...v}......u.. .
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&7CE0 BE 82 7D B9 0B 00 F3 A6-75 02 1F C3 BE F9 7C E8 ..}.....u.....|.
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&7CF0 A5 FF B4 00 CD 16 1F F9-C3 0D 0A 4E 6F 6E 2D 53 ...........Non-S
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&7D00 79 73 74 65 6D 20 64 69-73 6B 20 6F 72 20 64 69 ystem disk or di
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&7D10 73 6B 20 65 72 72 6F F2-0D 0A 52 65 70 6C 61 63 sk erro...Replac
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&7D20 65 20 61 6E 64 20 73 74-72 69 6B 65 20 61 6E 79 e and strike any
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&7D30 20 6B 65 79 20 77 68 65-6E 20 72 65 61 64 F9 0D key when read..
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&7D40 0A 00 CD 18 0D 0A 44 69-73 6B 20 42 6F 6F 74 20 ......Disk Boot
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&7D50 66 61 69 6C 75 72 E5 0D-0A 00 50 52 8B C6 BF 00 failur....PR....
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&7D60 02 F7 E7 03 D8 5A 58 C3-52 6F 62 65 72 74 20 4F .....ZX.Robert O
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&7D70 27 52 65 61 72 20 69 62-6D 62 69 6F 20 20 63 6F 'Rear ibmbio co
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&7D80 6D B0 69 62 6D 64 6F 73-20 20 63 6F 6D B0 C9 00 m.ibmdos com...
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&7D90 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&7DA0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&7DB0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&7DC0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&7DD0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&7DE0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&7DF0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&0000:7C00 EB 2F 14 00 00 00 60 00-20 37 2D 00 02 01 01 00 ./....`. 7-.....
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&0000:7C10 02 40 00 40 01 FE 01 00-08 00 01 00 00 00 00 00 .@.@............
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&0000:7C20 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&0000:7C30 00 FA 8C C8 8E D8 BA 00-00 8E D2 BC 00 7C FB A1 .............|..
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&0000:7C40 06 7C 8E D8 8E C0 BA 00-00 8B C2 CD 13 72 41 E8 .|...........rA.
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&0000:7C50 58 00 72 FB 2E 8B 0E 02-7C 51 BB 00 00 33 D2 B9 X.r.....|Q...3..
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&0000:7C60 08 00 BE 01 00 56 B0 01-B4 02 CD 13 72 22 5E 58 .....V......r"^X
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&0000:7C70 E8 E7 00 2B C6 74 14 FE-C5 B1 01 BE 08 00 3B C6 ...+.t........;.
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&0000:7C80 73 04 8B F0 EB 01 96 56-50 EB DD 2E FF 2E 04 7C s......VP......|
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&0000:7C90 BE 44 7D B8 42 7D 50 32-FF AC 24 7F 74 0B 56 B4 .D}.B}P2..$t.V.
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&0000:7CA0 0E BB 07 00 CD 10 5E EB-F0 C3 BB 00 00 B9 04 00 ......^.........
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&0000:7CB0 B8 01 02 CD 13 1E 72 34-8C C8 8E D8 BF 00 00 B9 ......r4........
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&0000:7CC0 0B 00 26 80 0D 20 26 80-8D 20 00 20 47 E2 F3 BF ..&.. &.. . G...
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&0000:7CD0 00 00 BE 76 7D B9 0B 00-FC F3 A6 75 0F BF 20 00 ...v}......u.. .
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&0000:7CE0 BE 82 7D B9 0B 00 F3 A6-75 02 1F C3 BE F9 7C E8 ..}.....u.....|.
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&0000:7CF0 A5 FF B4 00 CD 16 1F F9-C3 0D 0A 4E 6F 6E 2D 53 ...........Non-S
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&0000:7D00 79 73 74 65 6D 20 64 69-73 6B 20 6F 72 20 64 69 ystem disk or di
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&0000:7D10 73 6B 20 65 72 72 6F F2-0D 0A 52 65 70 6C 61 63 sk erro...Replac
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&0000:7D20 65 20 61 6E 64 20 73 74-72 69 6B 65 20 61 6E 79 e and strike any
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&0000:7D30 20 6B 65 79 20 77 68 65-6E 20 72 65 61 64 F9 0D key when read..
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&0000:7D40 0A 00 CD 18 0D 0A 44 69-73 6B 20 42 6F 6F 74 20 ......Disk Boot
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&0000:7D50 66 61 69 6C 75 72 E5 0D-0A 00 50 52 8B C6 BF 00 failur....PR....
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&0000:7D60 02 F7 E7 03 D8 5A 58 C3-52 6F 62 65 72 74 20 4F .....ZX.Robert O
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&0000:7D70 27 52 65 61 72 20 69 62-6D 62 69 6F 20 20 63 6F 'Rear ibmbio co
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&0000:7D80 6D B0 69 62 6D 64 6F 73-20 20 63 6F 6D B0 C9 00 m.ibmdos com...
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&0000:7D90 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&0000:7DA0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&0000:7DB0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&0000:7DC0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&0000:7DD0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&0000:7DE0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&0000:7DF0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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NOTE: When PCjs adds a BPB to the boot sector, the first 32 bytes will actually look like:
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&7C00 EB 2F 14 00 00 00 60 00-20 37 2D 00 02 01 01 00 ./....`. 7-.....
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&7C10 02 40 00 40 01 FE 01 00-08 00 01 00 00 00 00 00 .@.@............
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The addition of a BPB makes the disk image mountable by modern operating systems and does not
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otherwise affect the operation of the boot sector or any of the code below.
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NOTE: PCjs adds a BPB to the boot sector, which is why the first 32 bytes of the boot sector
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appear slightly different from the original [dump](#pc-dos-100-boot-sector) above. The addition of
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a BPB makes the disk image mountable by modern operating systems and does not otherwise affect the
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operation of the boot sector or any of the code below.
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First, let's disassemble the code from `start` (0x7C31):
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@ -439,6 +471,11 @@ And finally, `IBMBIO_COM` (0x7D76) and `IBMDOS_COM` (0x7D82):
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&7D78 6D 62 69 6F 20 20 63 6F-6D B0 69 62 6D 64 6F 73 mbio com.ibmdos
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&7D88 20 20 63 6F 6D B0 C9 00-00 00 00 00 00 00 00 00 com...........
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Interestingly, the [COMPAQ MS-DOS 1.11 Boot Sector](/disks/pcx86/dos/compaq/1.11/#compaq-ms-dos-111-boot-sector)
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is completely different from all PC-DOS 1.x boot sectors. The COMPAQ boot sector supports both 160Kb and 320Kb
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formats with less code and without requiring "patches", although that flexibility did require reading the first
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FAT sector, which PC-DOS 1.x boot sectors did not do.
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### Additional Information From [PC DOS Retro](https://sites.google.com/site/pcdosretro/doshist)
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- distributed on 1 160KB floppy disk
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@ -74,7 +74,7 @@ size of IBMDOS.COM is 6656, so the total number of bytes consumed by those two f
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### PC-DOS 1.10 Boot Sector
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The boot sector of the PC-DOS 1.11 disk image contains the following bytes:
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The boot sector of the PC-DOS 1.10 disk image contains the following bytes:
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00000000 eb 27 90 08 00 14 00 00 00 00 00 00 00 00 00 00 |.'..............|
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00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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@ -124,6 +124,11 @@ a 320Kb diskette is allocated a larger root directory (7 sectors instead of 4),
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out to sector #3 and head #1. The total number of sectors to read (0x14) remains the same as PC-DOS 1.00, but that
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value is now stored at offset 0x0005 (0x7C05) instead of 0x0002 (0x7C02).
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Interestingly, the [COMPAQ MS-DOS 1.11 Boot Sector](/disks/pcx86/dos/compaq/1.11/#compaq-ms-dos-111-boot-sector)
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is completely different from all PC-DOS 1.x boot sectors. The COMPAQ boot sector supports both 160Kb and 320Kb
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formats with less code and without requiring "patches", although that flexibility did require reading the first
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FAT sector, which PC-DOS 1.x boot sectors did not do.
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Using the PCjs Debugger, we can examine the boot sector in its native environment:
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bp &0000:7C00 hit
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@ -131,6 +136,46 @@ Using the PCjs Debugger, we can examine the boot sector in its native environmen
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AX=0000 BX=7C00 CX=0004 DX=0000 SP=0100 BP=E4B7 SI=0000 DI=0044
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SS=0030 DS=0040 ES=0000 PS=F296 V0 D0 I1 T0 S1 Z0 A1 P1 C0
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&0000:7C00 EB27 JMP 7C29
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>> db 7c00 l200
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&0000:7C00 EB 27 90 08 00 14 00 00-00 00 00 00 02 01 01 00 .'..............
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&0000:7C10 02 40 00 40 01 FE 01 00-08 00 01 00 00 00 00 00 .@.@............
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&0000:7C20 00 00 00 00 00 00 00 CD-19 FA 8C C8 8E D8 33 D2 ..............3.
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&0000:7C30 8E D2 BC 00 7C FB B8 60-00 8E D8 8E C0 33 D2 8B ....|..`.....3..
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&0000:7C40 C2 CD 13 72 69 E8 85 00-72 DD 2E 83 3E 03 7C 08 ...ri...r...>.|.
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&0000:7C50 74 06 2E C6 06 64 7D 02-BB 00 00 2E 8B 0E 03 7C t....d}........|
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&0000:7C60 51 B0 09 2A C1 B4 00 8B-F0 56 33 D2 33 C0 8A C5 Q..*.....V3.3...
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&0000:7C70 2E F6 36 64 7D 8A E8 8A-F4 8B C6 B4 02 CD 13 72 ..6d}..........r
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&0000:7C80 2D 5E 59 2E 29 36 05 7C-74 1F 8B C6 2E F7 26 65 -^Y.)6.|t.....&e
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&0000:7C90 7D 03 D8 FE C5 B1 01 51-BE 08 00 2E 3B 36 05 7C }......Q....;6.|
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&0000:7CA0 7C 05 2E 8B 36 05 7C EB-C0 EA 00 00 60 00 BE 67 |...6.|.....`..g
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&0000:7CB0 7D E8 02 00 EB FE 32 FF-2E AC 24 7F 74 0B 56 B4 }.....2...$t.V.
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&0000:7CC0 0E BB 07 00 CD 10 5E EB-EF C3 E9 33 FF BB 00 00 ......^....3....
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&0000:7CD0 B9 04 00 B8 01 02 CD 13-1E 72 33 8C C8 8E D8 BF .........r3.....
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&0000:7CE0 00 00 B9 0B 00 26 80 0D-20 26 80 4D 20 20 47 E2 .....&.. &.M G.
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&0000:7CF0 F4 BF 00 00 BE 8B 7D B9-0B 00 FC F3 A6 75 0F BF ......}......u..
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&0000:7D00 20 00 BE 97 7D B9 0B 00-F3 A6 75 02 1F C3 BE 1B ...}.....u.....
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&0000:7D10 7D E8 A2 FF B4 00 CD 16-1F F9 C3 0D 0A 4E 6F 6E }............Non
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&0000:7D20 2D 53 79 73 74 65 6D 20-64 69 73 6B 20 6F 72 20 -System disk or
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&0000:7D30 64 69 73 6B 20 65 72 72-6F 72 0D 0A 52 65 70 6C disk error..Repl
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&0000:7D40 61 63 65 20 61 6E 64 20-73 74 72 69 6B 65 20 61 ace and strike a
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&0000:7D50 6E 79 20 6B 65 79 20 77-68 65 6E 20 72 65 61 64 ny key when read
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&0000:7D60 79 0D 0A 00 01 00 02 0D-0A 44 69 73 6B 20 42 6F y........Disk Bo
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&0000:7D70 6F 74 20 66 61 69 6C 75-72 65 0D 0A 00 4D 69 63 ot failure...Mic
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&0000:7D80 72 6F 73 6F 66 74 2C 49-6E 63 20 69 62 6D 62 69 rosoft,Inc ibmbi
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&0000:7D90 6F 20 20 63 6F 6D 30 69-62 6D 64 6F 73 20 20 63 o com0ibmdos c
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&0000:7DA0 6F 6D 30 05 C6 06 77 2F-FF 83 7E FC 00 75 0B 80 om0...w/..~..u..
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&0000:7DB0 7E F7 3B 75 05 C6 06 76-2F FF 89 EC 5D CA 04 00 ~.;u...v/...]...
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&0000:7DC0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&0000:7DD0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&0000:7DE0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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&0000:7DF0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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NOTE: PCjs adds a BPB to the boot sector, which is why the first 32 bytes of the boot sector
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appear slightly different from the original [dump](#pc-dos-110-boot-sector) above. The addition of
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a BPB makes the disk image mountable by modern operating systems and does not otherwise affect the
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operation of the boot sector or any of the code below.
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>> tr
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AX=0000 BX=7C00 CX=0004 DX=0000 SP=0100 BP=E4B7 SI=0000 DI=0044
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SS=0030 DS=0040 ES=0000 PS=F296 V0 D0 I1 T0 S1 Z0 A1 P1 C0
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