Path: utzoo!attcan!darkover!telly!lethe!torsqnt!news-server.csri.toronto.edu!helios.physics.utoronto.ca!ists!yunexus!xrtll!silver
From: silver@xrtll.uucp (Hi Ho Silver)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 8088 RAM limit absolute?
Message-ID: <1990Jun5.022628.24656@xrtll.uucp>
Date: 5 Jun 90 02:26:28 GMT
References: <480@ra.MsState.Edu>
Organization: Not around here, pal!
Lines: 50

In article <480@ra.MsState.Edu> pam1@ra.MsState.Edu (Phillip A. McReynolds) writes:
$I understand that the 8088 and 8086 have an absolute memory limit of 640k. I

   No.  The IBM PC architecture has a limit of 640K of contiguous general-
purpose RAM.  The 8088 and 8086 have an absolute memory limit of 1M.  Some
PCs, depending on where in the memory range their display cards are, may
allow more than 640K of memory to be used.

$also understand that this problem can be circumvented to some extent with
$extended memory (XMS?) which can take it up to a full meg.  I have also heard
$that an XT cannot use any more than 1 meg of memory nor can it use Expanded
$Memory (EMS?).  Is this last part true?  Are there programs which would allow
$one to treat XMS as EMS?  I'm currently using the 384k as a RAM drive, but 
$would like to have some more actual RAM. 

   An XT cannot have extended memory because that's memory above the 1M
limit.  You only get extended memory on machines with a 286 or better CPU
in them.  An XT can, however, used expanded memory (LIM EMS 3.2, LIM EMS
4.0 and the like), which is basically a technique for bank-switching 16K
chunks of memory in and out of unused portions of the 1M address space
(typically, this is done above video memory and below the BIOS ROMs).  But
only programs which are written to use EMS can do so; you can't, for example,
take an XT with 640K RAM and 1M EMS and use any more than 640K unless the
programs you're using can use EMS (Symphony, for example, will use EMS if
it's available).

$What if I want something like 4 megs of RAM?  "Buy another computer," right?
$My system board is a Juko ST if that matters.  Also, I have a Paradise Basic
$VGA card whose manufacturer tells me is incompatible with EMS because IBM "set
$a standard and then didn't stick to it."

   Huh?  IBM allocated the 128K block above the end of the 640K main memory
for video boards, and that's the standard.  IBM designed the VGA card to
use that 128K block, and that's the standard.  No conflict; your manufacturer
is lying.  Either the card will work with EMS, or it isn't compatible with
the standard.

   As for wanting 4M of RAM, you can put tons of RAM into an XT with an
expanded memory board.  I believe EMS 4.0 allows up to 32M of expanded
memory, and you can put this into an XT if you feel like spending that
much money.  But it seems to me that unless you're doing something that
needs lots of memory and speed doesn't matter, you'd probably be better
off to get yourself a better computer - at least a 286 - with less than
4M of RAM than to take an XT and put 4M of RAM in it.  Just my personal
opinion, though.
-- 
   /Nikebo \ Nikebo says "Nikebo knows how to post.  Just do it."\silver@xrtll/
  /---------\_____________________________________________________\----------/
 /yunexus!xrtll!silver (L, not 1)\ Hi Ho Silver \   just silver for short   /
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