Path: utzoo!attcan!uunet!littlei!omepd!iwarpj!pcm
From: pcm@iwarpj.intel.com (Phil C. Miller)
Newsgroups: comp.os.minix
Subject: Re: EXTENDED/EXPANDED Memory on PC's
Message-ID: <4054@omepd.UUCP>
Date: 11 Jan 89 14:48:52 GMT
References: <6470@louie.udel.EDU>
Sender: news@omepd.UUCP
Reply-To: pcm@iwarpj.UUCP (Phil C. Miller)
Organization: Intel Corp., Hillsboro
Lines: 41

In article <6470@louie.udel.EDU> RM5I%DFVLROP1.BITNET@cunyvm.cuny.edu writes:
>Date: 10 January 1989, 12:32:46 MEZ
>From: RM5I     at DFVLROP1
>To:   info-min at udel.edu
>Subj: Extended/Expanded Memory on PC's

>I read a lot of things about using EXTENDED MEMORY with MINIX.
>What is about EXPANDED MEMORY on PC's with MINIX ? Maybe it is
>a little bit confusing (EXTENDED/EXPANDED MEMORY).

>What i mean is the extra memory above the 640k on a PC which is
>not a 286 or 386.
>Could please someone drop a line on this......

A brief correction and note of explanation...

First of all, expanded memory can be used on a 286 just fine; I assume
this is also true of a 386.

Extended memory is memory which is mapped to the address space above
1 Meg (0x100000).  For that reason, an operating system which runs in
REAL mode cannot access extended memory; operating systems like Microport
Unix run in PROTECTED mode, a mode unavailable on 8088's.  This is one
of the more important differences between an XT and an AT.

Expanded memory uses hardware tricks to make more memory available, but
always with a fixed amount available at a given time, 640k.  When more
memory is needed, a 64k-chunk of memory is "mapped out" and another is
"mapped in".  The new "chunk" is accessed using the same addresses as the
old "chunk" and the old chunk is unavailable.

In both cases, the user has the 16Mb of memory available for use; with
expanded memory, operating systems which run in REAL mode (most notably
DOS and MINIX) can have access to more than 640k.

>Regards Roland (rm5i@dfvlrop1) Bitnet/Earn

Phil Miller
Intel iWarp program
Intel Development Operations
Hillsboro, Oregon, USA