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Diffstat (limited to 'etc/etc.i386/INSTALL.mbr')
| -rw-r--r-- | etc/etc.i386/INSTALL.mbr | 271 |
1 files changed, 0 insertions, 271 deletions
diff --git a/etc/etc.i386/INSTALL.mbr b/etc/etc.i386/INSTALL.mbr deleted file mode 100644 index ebeaa0d04bf..00000000000 --- a/etc/etc.i386/INSTALL.mbr +++ /dev/null @@ -1,271 +0,0 @@ - How It Works -- Master Boot Record - - Version 1a - - by Hale Landis (landis@sugs.tware.com) - - -THE "HOW IT WORKS" SERIES - -This is one of several How It Works documents. The series -currently includes the following: - -* How It Works -- CHS Translation -* How It Works -- Master Boot Record -* How It Works -- DOS Floppy Boot Sector -* How It Works -- OS2 Boot Sector -* How It Works -- Partition Tables - - -MASTER BOOT RECORD - -This article is a disassembly of a Master Boot Record (MBR). The -MBR is the sector at cylinder 0, head 0, sector 1 of a hard disk. -An MBR is created by the FDISK program. The FDISK program of all -operating systems must create a functionally similar MBR. The MBR -is first of what could be many partition sectors, each one -containing a four entry partition table. - -At the completion of your system's Power On Self Test (POST), INT -19 is called. Usually INT 19 tries to read a boot sector from -the first floppy drive. If a boot sector is found on the floppy -disk, the that boot sector is read into memory at location -0000:7C00 and INT 19 jumps to memory location 0000:7C00. -However, if no boot sector is found on the first floppy drive, -INT 19 tries to read the MBR from the first hard drive. If an -MBR is found it is read into memory at location 0000:7c00 and INT -19 jumps to memory location 0000:7c00. The small program in the -MBR will attempt to locate an active (bootable) partition in its -partition table. If such a partition is found, the boot sector -of that partition is read into memory at location 0000:7C00 and -the MBR program jumps to memory location 0000:7C00. Each -operating system has its own boot sector format. The small -program in the boot sector must locate the first part of the -operating system's kernel loader program (or perhaps the kernel -itself or perhaps a "boot manager program") and read that into -memory. - -INT 19 is also called when the CTRL-ALT-DEL keys are used. On -most systems, CTRL-ALT-DEL causes an short version of the POST to -be executed before INT 19 is called. - -===== - -Where stuff is: - - The MBR program code starts at offset 0000. - The MBR messages start at offset 008b. - The partition table starts at offset 01be. - The signature is at offset 01fe. - -Here is a summary of what this thing does: - - If an active partition is found, that partition's boot record - is read into 0000:7c00 and the MBR code jumps to 0000:7c00 - with SI pointing to the partition table entry that describes - the partition being booted. The boot record program uses this - data to determine the drive being booted from and the location - of the partition on the disk. - - If no active partition table entry is found, ROM BASIC is - entered via INT 18. All other errors cause a system hang, see - label HANG. - -NOTES (VERY IMPORTANT): - - 1) The first byte of an active partition table entry is 80. - This byte is loaded into the DL register before INT 13 is - called to read the boot sector. When INT 13 is called, DL is - the BIOS device number. Because of this, the boot sector read - by this MBR program can only be read from BIOS device number - 80 (the first hard disk). This is one of the reasons why it - is usually not possible to boot from any other hard disk. - - 2) The MBR program uses the CHS based INT 13H AH=02H call to - read the boot sector of the active partition. The location of - the active partition's boot sector is in the partition table - entry in CHS format. If the drive is >528MB, this CHS must be - a translated CHS (or L-CHS, see my BIOS TYPES document). - No addresses in LBA form are used (another reason why LBA - doesn't solve the >528MB problem). - -===== - -Here is the entire MBR record (hex dump and ascii). - -OFFSET 0 1 2 3 4 5 6 7 8 9 A B C D E F *0123456789ABCDEF* -000000 fa33c08e d0bc007c 8bf45007 501ffbfc *.3.....|..P.P...* -000010 bf0006b9 0001f2a5 ea1d0600 00bebe07 *................* -000020 b304803c 80740e80 3c00751c 83c610fe *...<.t..<.u.....* -000030 cb75efcd 188b148b 4c028bee 83c610fe *.u......L.......* -000040 cb741a80 3c0074f4 be8b06ac 3c00740b *.t..<.t.....<.t.* -000050 56bb0700 b40ecd10 5eebf0eb febf0500 *V.......^.......* -000060 bb007cb8 010257cd 135f730c 33c0cd13 *..|...W.._s.3...* -000070 4f75edbe a306ebd3 bec206bf fe7d813d *Ou...........}.=* -000080 55aa75c7 8bf5ea00 7c000049 6e76616c *U.u.....|..Inval* -000090 69642070 61727469 74696f6e 20746162 *id partition tab* -0000a0 6c650045 72726f72 206c6f61 64696e67 *le.Error loading* -0000b0 206f7065 72617469 6e672073 79737465 * operating syste* -0000c0 6d004d69 7373696e 67206f70 65726174 *m.Missing operat* -0000d0 696e6720 73797374 656d0000 00000000 *ing system......* -0000e0 00000000 00000000 00000000 00000000 *................* -0000f0 TO 0001af SAME AS ABOVE -0001b0 00000000 00000000 00000000 00008001 *................* -0001c0 0100060d fef83e00 00000678 0d000000 *......>....x....* -0001d0 00000000 00000000 00000000 00000000 *................* -0001e0 00000000 00000000 00000000 00000000 *................* -0001f0 00000000 00000000 00000000 000055aa *..............U.* - -===== - -Here is the disassembly of the MBR... - -This sector is initially loaded into memory at 0000:7c00 but -it immediately relocates itself to 0000:0600. - - BEGIN: NOW AT 0000:7C00, RELOCATE - -0000:7C00 FA CLI disable int's -0000:7C01 33C0 XOR AX,AX set stack seg to 0000 -0000:7C03 8ED0 MOV SS,AX -0000:7C05 BC007C MOV SP,7C00 set stack ptr to 7c00 -0000:7C08 8BF4 MOV SI,SP SI now 7c00 -0000:7C0A 50 PUSH AX -0000:7C0B 07 POP ES ES now 0000:7c00 -0000:7C0C 50 PUSH AX -0000:7C0D 1F POP DS DS now 0000:7c00 -0000:7C0E FB STI allow int's -0000:7C0F FC CLD clear direction -0000:7C10 BF0006 MOV DI,0600 DI now 0600 -0000:7C13 B90001 MOV CX,0100 move 256 words (512 bytes) -0000:7C16 F2 REPNZ move MBR from 0000:7c00 -0000:7C17 A5 MOVSW to 0000:0600 -0000:7C18 EA1D060000 JMP 0000:061D jmp to NEW_LOCATION - - NEW_LOCATION: NOW AT 0000:0600 - -0000:061D BEBE07 MOV SI,07BE point to first table entry -0000:0620 B304 MOV BL,04 there are 4 table entries - - SEARCH_LOOP1: SEARCH FOR AN ACTIVE ENTRY - -0000:0622 803C80 CMP BYTE PTR [SI],80 is this the active entry? -0000:0625 740E JZ FOUND_ACTIVE yes -0000:0627 803C00 CMP BYTE PTR [SI],00 is this an inactive entry? -0000:062A 751C JNZ NOT_ACTIVE no -0000:062C 83C610 ADD SI,+10 incr table ptr by 16 -0000:062F FECB DEC BL decr count -0000:0631 75EF JNZ SEARCH_LOOP1 jmp if not end of table -0000:0633 CD18 INT 18 GO TO ROM BASIC - - FOUND_ACTIVE: FOUND THE ACTIVE ENTRY - -0000:0635 8B14 MOV DX,[SI] set DH/DL for INT 13 call -0000:0637 8B4C02 MOV CX,[SI+02] set CH/CL for INT 13 call -0000:063A 8BEE MOV BP,SI save table ptr - - SEARCH_LOOP2: MAKE SURE ONLY ONE ACTIVE ENTRY - -0000:063C 83C610 ADD SI,+10 incr table ptr by 16 -0000:063F FECB DEC BL decr count -0000:0641 741A JZ READ_BOOT jmp if end of table -0000:0643 803C00 CMP BYTE PTR [SI],00 is this an inactive entry? -0000:0646 74F4 JZ SEARCH_LOOP2 yes - - NOT_ACTIVE: MORE THAN ONE ACTIVE ENTRY FOUND - -0000:0648 BE8B06 MOV SI,068B display "Invld prttn tbl" - - DISPLAY_MSG: DISPLAY MESSAGE LOOP - -0000:064B AC LODSB get char of message -0000:064C 3C00 CMP AL,00 end of message -0000:064E 740B JZ HANG yes -0000:0650 56 PUSH SI save SI -0000:0651 BB0700 MOV BX,0007 screen attributes -0000:0654 B40E MOV AH,0E output 1 char of message -0000:0656 CD10 INT 10 to the display -0000:0658 5E POP SI restore SI -0000:0659 EBF0 JMP DISPLAY_MSG do it again - - HANG: HANG THE SYSTEM LOOP - -0000:065B EBFE JMP HANG sit and stay! - - READ_BOOT: READ ACTIVE PARTITION BOOT RECORD - -0000:065D BF0500 MOV DI,0005 INT 13 retry count - - INT13RTRY: INT 13 RETRY LOOP - -0000:0660 BB007C MOV BX,7C00 -0000:0663 B80102 MOV AX,0201 read 1 sector -0000:0666 57 PUSH DI save DI -0000:0667 CD13 INT 13 read sector into 0000:7c00 -0000:0669 5F POP DI restore DI -0000:066A 730C JNB INT13OK jmp if no INT 13 -0000:066C 33C0 XOR AX,AX call INT 13 and -0000:066E CD13 INT 13 do disk reset -0000:0670 4F DEC DI decr DI -0000:0671 75ED JNZ INT13RTRY if not zero, try again -0000:0673 BEA306 MOV SI,06A3 display "Errr ldng systm" -0000:0676 EBD3 JMP DISPLAY_MSG jmp to display loop - - INT13OK: INT 13 ERROR - -0000:0678 BEC206 MOV SI,06C2 "missing op sys" -0000:067B BFFE7D MOV DI,7DFE point to signature -0000:067E 813D55AA CMP WORD PTR [DI],AA55 is signature correct? -0000:0682 75C7 JNZ DISPLAY_MSG no -0000:0684 8BF5 MOV SI,BP set SI -0000:0686 EA007C0000 JMP 0000:7C00 JUMP TO THE BOOT SECTOR - WITH SI POINTING TO - PART TABLE ENTRY - -Messages here. - -0000:0680 ........ ........ ......49 6e76616c * Inval* -0000:0690 69642070 61727469 74696f6e 20746162 *id partition tab* -0000:06a0 6c650045 72726f72 206c6f61 64696e67 *le.Error loading* -0000:06b0 206f7065 72617469 6e672073 79737465 * operating syste* -0000:06c0 6d004d69 7373696e 67206f70 65726174 *m.Missing operat* -0000:06d0 696e6720 73797374 656d00.. ........ *ing system. * - -Data not used. - -0000:06d0 ........ ........ ......00 00000000 * .....* -0000:06e0 00000000 00000000 00000000 00000000 *................* -0000:06f0 00000000 00000000 00000000 00000000 *................* -0000:0700 00000000 00000000 00000000 00000000 *................* -0000:0710 00000000 00000000 00000000 00000000 *................* -0000:0720 00000000 00000000 00000000 00000000 *................* -0000:0730 00000000 00000000 00000000 00000000 *................* -0000:0740 00000000 00000000 00000000 00000000 *................* -0000:0750 00000000 00000000 00000000 00000000 *................* -0000:0760 00000000 00000000 00000000 00000000 *................* -0000:0770 00000000 00000000 00000000 00000000 *................* -0000:0780 00000000 00000000 00000000 00000000 *................* -0000:0790 00000000 00000000 00000000 00000000 *................* -0000:07a0 00000000 00000000 00000000 00000000 *................* -0000:07b0 00000000 00000000 00000000 0000.... *............ * - -The partition table starts at 0000:07be. Each partition table -entry is 16 bytes. This table defines a single primary partition -which is also an active (bootable) partition. - -0000:07b0 ........ ........ ........ ....8001 * ....* -0000:07c0 0100060d fef83e00 00000678 0d000000 *......>....x....* -0000:07d0 00000000 00000000 00000000 00000000 *................* -0000:07e0 00000000 00000000 00000000 00000000 *................* -0000:07f0 00000000 00000000 00000000 0000.... *............ * - -The last two bytes contain a 55AAH signature. - -0000:07f0 ........ ........ ........ ....55aa *..............U.* - -/end/ --- -\\===============\\=======================\\ - \\ Hale Landis \\ 303-548-0567 \\ - // Niwot, CO USA // landis@sugs.tware.com // -//===============//=======================// |