Other Read/Write Memory Usage - IBM 5150 Technical Reference

Other Read/Write Memory Usage
The IBM BIOS routines use 256 bytes of memory from absolute
hex 400 to hex 4FF. Locations hex 400 to 407 contain the base
addresses of any RS-232C cards attached to the system.
Locations hex 408 to 40F contain the base addresses of the
Printer Adapter.
Memory locations hex 300 to 3FF are used as a stack area during
the power-on initialization, and bootstrap when control is passed
to it from power-on. If the user desires the stack in a different
area, the area must be set by the application.
5-8
System
BIOS