Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!uwm.edu!cs.utexas.edu!asuvax!noao!arizona!coyote!jmh
From: jmh@coyote.uucp (John Hughes)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 8088 RAM limit absolute?
Message-ID: <1990Jun1.061809.1388@coyote.uucp>
Date: 1 Jun 90 06:18:09 GMT
References: <480@ra.MsState.Edu>
Reply-To: jmh@coyote.UUCP (John Hughes)
Distribution: comp.sys.ibm.pc
Organization: Datalog Consulting, Tucson, AZ
Lines: 37

In article <480@ra.MsState.Edu> pam1@ra.MsState.Edu (Phillip A. McReynolds) writes:
>I assume that this is a "most frequently asked question," but I don't seem to
>see any answers on the list so I will go ahead.  
>
>I understand that the 8088 and 8086 have an absolute memory limit of 640k. I
>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. 
>
>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."
>
Actually, the 8086 and 8088 variants of the iAPX86 processor family will
directly address up to 1 meg of memory. It is DOS that will not normally
recognize anything above 640K. The upper memory area is used for things
like video RAM, ROM/EPROM devices in controller cards, and the system
ROM BIOS (and ROM Basic in older IBM PC's). You could use some of that
memory, if you write or have software that knows about it (this is just what
an EMS driver does, it uses 128K or so to swap memory to and from the
EMS board).

There are quite a few reference books out detailing the memory usage and
EMS standards for the PC family. I recommend "Advanced MS-DOS", by Ray
Duncan, published by Microsoft Press.



-- 
==============================================================================
John M. Hughes                 "The most incomprehensible thing about us is 
jmh@coyote.UUCP                our cheerfulness..." - Nietzsche
...arizona!coyote!jmh          (Philosophers are a truly strange bunch....)