EXE header structure
Source - The Programmer's PC Sourcebook, 2nd Edition, table 2.27

   Offset  Length  Usual  Description
      00h    word  4d5ah  EXE file signature
      02h    word         Length of file (modulo 512)
      04h    word         Size of file, including header
      06h    word   Number of relocation table items
      08h    word   Size of header
      0ah    word   Minimum paragraphs (16 bytes) needed above program
      0ch    word   Maximum paragraphs (16 bytes) desired above program
      0eh    word   Displacement of stack segment in module (relative to
                    start of program, in paragraphs)
      10h    word   Contents of SP register at entry
      12h    word   Checksum (two's complement)
      14h    word   Contents of IP register at entry
      16h    word   Displacement of entry code module (relative to start
                    of program, in paragraphs)
      18h    word   Offset to first relocation item in file (relative to
                    start of file, in bytes)
      1ah    word   Overlay number (0 for resident part of program)
*     1ch  varies   Variable reserved space
*  varies  varies   Relocation table
*  varies  varies   Variable reserved space
*  varies  varies   Program and data segments
*  varies  varies   Stack segment

* - Not in DOS 5.0 EXEHEADER structure