lane@cs.dal.ca (John Wright/Dr. Pat Lane) (02/24/90)
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
Cdn/Eannet:lane@cs.dal.cdn Uucp:lane@dalcs.uucp or {uunet watmath}!dalcs!lane
Arpa:lane%dalcs.uucp@uunet.uu.net Internet:lane@cs.dal.caphil@pepsi.amd.com (Phil Ngai) (02/27/90)
In article <1990Feb24.145530.17100@cs.dal.ca> lane@cs.dal.ca (John Wright/Dr. Pat Lane) writes: |Here's another issue I'd like some authorative, definative information |on (or pointers to published articles). This is a subject near and dear to my heart. I don't know of a lot of articles on this. PC Magazine had one on add-in cards but it didn't talk about chipsets and it didn't get as explicit as I will. |Most 286's advertised these days offer "LIM 4.0 EMS support" and use Unfortuately this is almost meaningless. |one of several brands of "chip sets" on the motherboards. I've |encountered three brands: Chips&Technologies (C&T), Neat, and VLSI. C&T makes NEAT. |I gather that the EMS support is entirely (?) a function of the chip |set. EMS is part hardware and part software. If the hardware isn't there, there's nothing the software can do under a 286. |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). With the C&T NEAT, if you have more than 1 meg, the 384K is only available as shadow. It can not be used as extended. |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 The early VLSI chip-sets have no hardware support for EMS and have to depend on SW only implementations. Their "TOPCAT" line is better but not ideal. |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. This is true but this is not full 4.0. The full EMS 4.0 allows paging into any part of the 1 meg conventional, including the 640k. NEAT can not do this. |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. Nope, the problem is the 4.0 spec was forced to be watered down by the committee members. There are newer chip sets coming out, with better features. Finding them is a difficult task. -- Phil Ngai, phil@amd.com {uunet,decwrl,ucbvax}!amdcad!phil When guns are outlawed, only governments will have guns.