E X E C U T A B L E  File Formats





EXE
                     .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)

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