Browse Prior Art Database

Extending Available System Memory by User-Selectable Rom-to-Ram Configuration Remap

IP.com Disclosure Number: IPCOM000101619D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 83K

Publishing Venue

IBM

Related People

Bealkowski, R: AUTHOR [+2]

Abstract

This article describes a technique for use in a computer system which allows read-only memory (ROM)-to-random-access memory (RAM) remap to be user-selectable via software based on configuration information set by the user.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Extending Available System Memory by User-Selectable Rom-to-Ram Configuration Remap

       This article describes a technique for use in a computer
system which allows read-only memory (ROM)-to-random-access memory
(RAM) remap to be user-selectable via software based on configuration
information set by the user.

      During the power-on self-test (POST) process in certain
personal computers (PCs) the 128Kb of POST, basic input output
services (BIOS), and advanced BIOS (ABIOS) contained in the ROM in
the E000h and F000h segments (memory addresses E0000h through FFFFFh)
is copied to a 128Kb section of the system RAM.  The ROM at segments
E000h and F000h is removed from the address space.  The 128Kb of RAM
which received the copy of the ROM image is placed into the same
address space that the ROM used to occupy.  This remapping of the
E000h and F000h segments provides a performance improvement since it
takes less time to obtain instructions from system RAM than from
system ROM.  However, since 128Kb of RAM is now occupied by the ROM
contents, the available system memory size is decreased by 128Kb.

      The current POST process for copying ROM to RAM is shown in
Fig.  1.  Briefly, when the system is powered on, the POST process
performs some initial system checkout. When this is complete, POST
copies the E000h and F000h ROM segments to RAM, and then continues
the process to complete system initialization and to load the
operating system.

      The data used to configure some PC systems is established
during system set up and is stored in nonvolatile system memory
(NVRAM).  Each time the system unit is powered on, the data is
retrieved from NVRAM during the POST proce...