Path: utzoo!attcan!uunet!husc6!think!ames!ncar!noao!asuvax!nud!mcdchg!clyde!rjs@moss.ATT.COM
From: rjs@moss.ATT.COM
Newsgroups: comp.sys.ibm.pc
Subject: Expanded vs. Extended mnemonic.
Message-ID: <36835@clyde.ATT.COM>
Date: 23 Nov 88 22:57:36 GMT
Sender: nuucp@clyde.ATT.COM
Lines: 27


A simple mnemonic was provided by someone on the net a few months ago
to help remember the difference between expanded and extended memory.

Extended conjures the image of long and thin: the address range of extended
memory in an 80[23]86 based machine is longer than the 0-1M range of an
8086 based machine, while each address represents one byte.

Expanded conjures the image of short and fat: the address range of expanded
memory still falls withing the 8086 0-1M range, but a small (64K I think)
section above the 0-640K range assigned to general purpose RAM can be mapped
to many different arrays of 64K bytes.  Thus each address represents a
collection of bytes.  A bios/driver/DOS/? function call is used to pick the
64K array which will be accessed by subsequent use of the 64K expanded memory
range.

While my description above may not be entirely technically accurate, the
mnemonic sure helps me quickly remember which memory addressing scheme is
which when I run across the terms in an article or ad.  Hope it helps you too.

	Robert Snyder
	{att|ihnp4|clyde}!moss!rjs
	rjs@moss.ATT.COM
	(201) 386-4467

The above statements are my own thoughts and observations and are not
intended to represent my employer's position on the subject(s).