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August 14, 2024 01:05
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Save andydude/3c599caa975f62bc886feb1b77133931 to your computer and use it in GitHub Desktop.
First attempt at a master boot record.
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| [bits 16] | |
| [org 0x7C00] | |
| start: | |
| cli | |
| xor si,si | |
| mov ss,si | |
| mov sp,0x7DBE | |
| popa | |
| mov es,si | |
| mov ax,0x201 | |
| int 0x13 | |
| jmp 0x0:0x7E00 | |
| times 0x1BC - ($-$$) db 0 | |
| mbr: | |
| dw 0x7E00 | |
| dw 0x0180 | |
| dw 0x0001 | |
| dw 0x7F0B | |
| dw 0xFDBF | |
| dw 0x003F | |
| dw 0x0000 | |
| dw 0x40C1 | |
| dw 0x005E | |
| times 0x1FE - ($-$$) db 0 | |
| sig: | |
| dw 0xAA55 |
I believe the original purpose was to load a VBR and jump do it.
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Not sure about the purpose, but if you ever plan to use this for anything serious, some BIOSes require the first instruction (first 2 bytes) to be "33 C0" ("xor ax, ax", but alternatively encoded) to identify the MBR as "modern" and disable workarounds for old DOS variants. Learned this the hard way with builder-hex0.