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From: lane@cs.dal.ca (John Wright/Dr. Pat Lane)
Newsgroups: comp.sys.ibm.pc
Subject: Question: 286 Chipsets and their handling of EMS support
Message-ID: <1990Feb24.145530.17100@cs.dal.ca>
Date: 24 Feb 90 14:55:30 GMT
Organization: Math, Stats & CS, Dalhousie University, Halifax, NS, Canada
Lines: 42

Hi there:

Here's another issue I'd like some authorative, definative information
on (or pointers to published articles).

Most 286's advertised these days offer "LIM 4.0 EMS support" and use
one of several brands of "chip sets" on the motherboards.  I've
encountered three brands: Chips&Technologies (C&T), Neat, and VLSI.
I gather that the EMS support is entirely (?) a function of the chip
set.

Further, I am coming to realize (partly by seeing articles here) that
not all chip sets are created equal (somewhat like the situation with
the various brands of BIOS's).

There seems to be some discussion ongoing about different systems
handling of ROM shadowing (ie. whether you can turn it off and whether
you get the 384K back as extended memory).

I'm wondering more about EMS support and full LIM 4.0 compliance.  In
particular some chip-sets (such as VLSI) seem to do a "software-like"
emulation of EMS, setting up a page buffer in your conventional memory
and flipping in & out of protected mode to copy pages to&from pages in
extended memory.  Others (Neat's, I'm told) do a more "386-like" full
implementation of LIM 4.0, switching the required EMS page into an
address space between 640K to 1Meg so that no real RAM is required
for the page buffer.

It seems to me that many of the systems advertising "full LIM 4.0" do
not in fact achieve that and perhaps are, to some extent, guilty of
false advertising.

I wonder if someone could confirm/correct the above rambings, provide
more detail, and specifics on what chipset brands have what capabilities.

Thanks as always.

-- 
John Wright      //////////////////     Phone:  902-424-3805  or  902-424-6527
Post: c/o Dr Pat Lane, Biology Dept, Dalhousie U, Halifax N.S., CANADA B3H-4H8 
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