This function provides storage and retrieval of any of 8 words in extended BIOS RAM. The built-in applications use the first few of these locations. The others are available. Inputs include a direction flag by specifying Store or Retrieve, and an index specifying the word location in the mailbox. In addition, if the operation is a store, the word to be stored is an input. The service exits CS iff the value in AL is invalid.
Mailbox Allocation
Index Usage ================================================= 00h TSR keybez load segment. ------------------------------------------------- 01h System Manager loaded if value is 7072h. ------------------------------------------------- 02h /// Currently Unallocated /// ------------------------------------------------- 03h /// Currently Unallocated /// ------------------------------------------------- 04h /// Currently Unallocated /// ------------------------------------------------- 05h /// Currently Unallocated /// ------------------------------------------------- 006h /// Currently Unallocated /// ------------------------------------------------- 07h /// Currently Unallocated /// -------------------------------------------------