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

IBM 5150 Specifications

General

Processor	Intel 8088
Clock Speed	4.77 MHz
RAM	16 KB - 256 KB
Manufacturer	IBM
Model	5150
Release Year	1981
Storage	5.25-inch floppy drives
Graphics	MDA or CGA
Operating System	IBM PC DOS
Ports	Cassette, keyboard
Expansion Slots	5