.EXE - DOS EXE File Structure
Offset Size Description 00 word "MZ" - Link file .EXE signature (Mark Zbikowski?) 02 word length of image mod 512 04 word size of file in 512 byte pages 06 word number of relocation items following header 08 word size of header in 16 byte paragraphs, used to locate the beginning of the load module 0A word min # of paragraphs needed to run program 0C word max # of paragraphs the program would like 0E word offset in load module of stack segment (in paras) 10 word initial SP value to be loaded 12 word negative checksum of pgm used while by EXEC loads pgm 14 word program entry point, (initial IP value) 16 word offset in load module of the code segment (in paras) 18 word offset in .EXE file of first relocation item 1A word overlay number (0 for root program) - relocation table and the program load module follow the header - relocation entries are 32 bit values representing the offset into the load module needing patched - once the relocatable item is found, the CS register is added to the value found at the calculated offset Registers at load time of the EXE file are as follows: AX: contains number of characters in command tail, or 0 BX:CX 32 bit value indicating the load module memory size DX zero SS:SP set to stack segment if defined else, SS = CS and SP=FFFFh or top of memory. DS set to segment address of EXE header ES set to segment address of EXE header CS:IP far address of program entry point, (label on "END" statement of program)