Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!vrdxhq!tom
From: tom@vrdxhq.UUCP (Tom Welsh)
Newsgroups: comp.sys.ibm.pc
Subject: Re: MS-DOS Versions
Message-ID: <2623@vrdxhq.UUCP>
Date: Mon, 15-Dec-86 09:32:52 EST
Article-I.D.: vrdxhq.2623
Posted: Mon Dec 15 09:32:52 1986
Date-Received: Tue, 16-Dec-86 23:36:03 EST
References: <2418@ihlpa.UUCP> <174200005@uiucuxc> <1793@ncoast.UUCP> <243@wolf.UUCP>
Organization: Verdix Corporation, Chantilly, VA
Lines: 38
Summary: Yes, it's the IBM PC

> 
> I have a short program which I got on a Bulletin Board which lets me use
> DOS and up to 704K of memory as long as you don't have an EGA. The 640K
> limitation seems to be an IBM PC limitation not a MSDOS limitation.
> -- 

The Intel 8088, 8086, 80186, 80286 (in real address mode), and 80386 (in
8086 mode) all support up to 1 megabyte of addressing.

The 640k limitation in the PC is caused by the fact that the PC manufacturers
chose to use certain areas for display adapters, ROM cartridges, etc.

Here's the memory map for 1 MB PC family, per Peter Norton's book ...

Starting address      contents

0xF0000               Permanent ROM area (BIOS, BASIC, diagnostics)
0xE0000               Cartridge ROM
0xD0000               Cartridge ROM
0xC0000               BIOS Extensions (XT disk)
0xB0000               Conventional display memory (PC, XT, AT)
0xA0000               Display memory expansion
0x90000               Working RAM (addresses are 576k through 640k-1)
0x80000               Working RAM (addresses are 512k through 576k-1)
0x70000               Working RAM (addresses are 448k through 512k-1)
0x60000               Working RAM (addresses are 384k through 448k-1)
0x50000               Working RAM (addresses are 329k through 384k-1)
0x40000               Working RAM (addresses are 256k through 320k-1)
0x30000               Working RAM (addresses are 192k through 256k-1)
0x20000               Working RAM (addresses are 128k through 192k-1)
0x10000               Working RAM (addresses are 64k through 128k-1)
0x00000               Working RAM (addresses are 0 through 64k-1) (used
                      by system software (BIOS,DOS) for work area

> ---------------------------------
> Mark C. DiVecchio 10435 Mountain Glen Terrace, San Diego, CA 92131
> K3FWT			Home of PC-VT and LPTx		619-566-6810
> sdcsvax!man!wolf!markd