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Technical Reference Guide
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition - September 1997
8-1
Chapter 8
BIOS ROM
8.
Chapter 8 BIOS ROM
8.1
INTRODUCTION
The Basic Input/Output System (BIOS) of the computer is a collection of machine language
programs stored as firmware in read-only memory (ROM). The BIOS ROM includes such
functions as Power-On Self Test (POST), PCI device initialization, Plug ‘n Play support, power
management activities, and Setup. This chapter includes the following topics:
♦ Boot Functions (8.2) page 8-2
♦ Accessing configuration memory (8.3) page 8-3
♦ Client management support (8.4) page 8-5
♦ PnP support (8.5) page 8-17
♦ Power management support (8.6) page 8-18
The firmware contained in the BIOS ROM supports the following operating systems:
♦ DOS 6.2
♦ Windows 3.1
♦ Windows for Workgroups 3.11
♦ Windows 95
♦ Windows NT 3.5
♦ OS/2 ver 2.1
♦ OS/2 Warp
♦ SCO Unix
The microprocessor accesses the BIOS ROM as a 128-KB block from E0000h to FFFFFh. The
BIOS data is shadowed in a 64-KB block in the upper memory area. The BIOS segments are
dynamically paged in and out of the 64-KB block as they are needed.
NOTE:
This chapter describes BIOS in general and focuses on aspects of BIOS unique
to this particular system. For detailed information regarding the BIOS, refer to the
Compaq Basic Input/Output System Technical Reference Guide.