DOS Version 4
   New Features in DOS Version 4
   Interrupt 21H Functions in DOS Version 4
     Function 33H (decimal 51): Get/Set System Value
     Function 44H (decimal 68): IOCTL--I/O Control for Devices
     Function 65H (decimal 101): Get Extended Country Information
     Function 6CH (decimal 108): Extended Open/Create
   Interrupts 25H and 26H
   The DOS Version 4 Disk Boot Sector
     The Extended BIOS Parameter Block
     The Volume Serial Number
   A Sample Routine
   DOS Version 4 in Perspective