I'm no fan of the IBM PC or of MS-DOS, really I'm not.
http://dosmandrivel.blogspot.co.za/2011/04/all-those-floppy-disk-formats.html However, copy protection fascinates me, and of course the IBM PC wasn't immune to this.
Copy protection has a major Achilles heel. The BIOS needs to be able to read the first sector of the first track. From here on in you can obfuscate as much as you want to, but a determined hacker will always be able to trace the boot, whether it's a PC or an Apple.
MS-DOS 1.0 supported 8 sectors per track, 40 tracks, single-sided disks. MS-DOS 1.1 added double-sided disk support, and MS-DOS 2.0 changed to 9 sectors per track to give the traditional 360 kilobyte floppy (720 sectors of 512 bytes, 360 (40 x 9) sectors per side). If you're morbidly curios, MS-DOS also supports 77 track 8" floppies, using the DEC standard, not the IBM standard... I wouldn't mind getting hold of a NEC APC -- MS-DOS 2.11 on 8" floppies, with a uPD7220 graphics controller.
C>debug -l 100 1 0 1 (Load at address 0x100, from drive 1 (my floppy is B), sector 0, 1 sector) -n dos32.bin (Name of file to save) rcx (BX:CX holds the length to save) :200 w 100 (Write starting at address 0x100)
If you want to know what a typical DOS bootsector looks like, look here. The Planetfall bootsector is not even close.
00007C00 FA cli 00007C01 EB19 jmp 000007C1Ch 00007C03 8ED8 mov ds,ax I have no idea what this cruft is 00007C05 BB7800 mov bx,0078h 00007C08 B97900 mov cx,0079h 00007C0B BAC007 mov dx,07C0h 00007C0E 8B37 mov si,[bx] 00007C10 8B7F02 mov di,[bx+02h] 00007C13 890F mov [bx],cx 00007C15 895702 mov [bx+02h],dx 00007C18 8CC8 mov ax,cs 00007C1A 8ED8 mov ds,ax 00007C1C BA0000 mov dx,0000h DX = 0x0000 00007C1F 8ED2 mov ss,dx SS = 0x0000 00007C21 BB007C mov bx,7C00h BX = 0x7C00 00007C24 8BE3 mov sp,bx SP = 0x7C00 So the stack grows down from 0x07C00 00007C26 FB sti Enable interrupts 00007C27 B86000 mov ax,0060h 00007C2A 8ED8 mov ds,ax DS = 0x0060 00007C2C 8EC0 mov es,ax ES = 0x0060, this is used in the next block of code 00007C2E 2BC0 sub ax,ax AX = 0, AH = 0, Reset disk drive 00007C30 2BD2 sub dx,dx DL = 0, first floppy 00007C32 CD13 int 13h Reset disk drive 00007C34 BA0300 mov dx,0003h 00007C37 2BDB sub bx,bx BX = 0x0000, ES:BX = 0x00600, Buffer address (IBM PC reserved memory spans 0x00000 to 0x0005FF) 00007C39 B501 mov ch,01h CH = 0x01, Cylinder 1 LOOP1: 00007C3B 52 push dx 00007C3C B101 mov cl,01h CL = 0x01, Sector 1 00007C3E 51 push cx 00007C3F 2BD2 sub dx,dx DH = 0x00, Head 0. DL = 0x00, first floppy 00007C41 B80802 mov ax,0208h AH = 0x02, Read Sectors from Drive. AL = 0x08, eight sectors (of 512 bytes each), 0x60000 to 0x60FFF 00007C44 CD13 int 13h Read Sectors 00007C46 721C jb 000007C64h On error (CF=1) 00007C48 59 pop cx 00007C49 FEC5 inc ch Next cylinder 00007C4B 81C30010 add bx,word 1000h BX = 0x1000, 0x2000 00007C4F 5A pop dx 00007C50 4A dec dx 00007C51 75E8 jnz 000007C3Bh If DX not zero, goto LOOP1: So here we have sectors 1-8 of cylinder 1 at 0x00600 to 0x015FF sectors 1-8 of cylinder 2 at 0x01600 to 0x025FF sectors 1-8 of cylinder 3 at 0x02600 to 0x035FF 00007C53 EB0A jmp 000007C5Fh GO: 00007C55 8ED8 mov ds,ax I have no idea what this cruft is 00007C57 BB7800 mov bx,0078h 00007C5A 8937 mov [bx],si 00007C5C 897F02 mov [bx+02h],di GO: 00007C5F 06 push es ES is still 0x0060 00007C60 2BC0 sub ax,ax AX = 0x0000 00007C62 50 push ax 00007C63 CB retf Return Far, pop CS and the Instruction Pointer (IP) = 0x00600 ERROR: 00007C64 2BDB sub bx,bx 00007C66 B049 mov al,49h Character "I" 00007C68 B40E mov ah,0Eh Teletype output 00007C6A CD10 int 10h 00007C6C B04C mov al,4Ch Character "L" 00007C6E B40E mov ah,0Eh 00007C70 CD10 int 10h 00007C72 B04C mov al,4Ch Character "L" 00007C74 B40E mov ah,0Eh 00007C76 CD10 int 10h 00007C78 F4 hlt And die. 00007C79 CF iret I have no idea what this cruft is 00007C7A 0225 add ah,[di] 00007C7C 0304 add ax,[si] 00007C7E 2AFF sub bh,bh 00007C80 50 push ax 00007C81 F619 neg byte [bx+di] 00007C83 04
Fairly uninspired. They had all that space to store interesting messages. And there's a lot of redundant code. Offensive, to an old Apple ][ hacker.
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