BerandaComputers and TechnologyMIOS: IBM 5150 BIOS Replacement Project

MIOS: IBM 5150 BIOS Replacement Project

This
webpage describes the MIOS Project. MIOS is a
chip-for-chip replacement of the BIOS (Basic Input Output System) on
the IBM 5150 Personal Computer. On the IBM PC the BIOS is contained in
a ROM IC Chip located on the motherboard at socket location U33. The IC
is socketed and can be replaced with a custom ROM containing
custom code. 

The purpose of this project is to explore controlling the IBM PC
hardware in non-standard ways. The purpose is not to replace the BIOS
with another BIOS that does exactly the same thing! We are going to
describe how MIOS works by describing the path we took for development.

We started this project by considering other BIOS replacement software.
Notably for the IBM PC there is a diagnostic ROM replacement known as
the Landmark/Supersoft package, as described here: Minus
Zero Degrees

The Landmark/Supersoft code is unique. By burning the code
to ROM and placing in BIOS location U33 it is possible to boot the IBM
PC and perform a series of diagnostic tests, with the results
reported on the screen in real time. A photo of a typical display
screen is shown in Figure 1.  The
key point about the
diagnostic
ROM is the fact the code is completely controlling the PC
hardware: There is no DOS operating system. There is no BIOS
.

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