Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!rpi!rpitsmts!forumexp
From: Greg_d._Moore@mts.rpi.edu (Commander Krugannal)
Newsgroups: comp.sys.ibm.pc.misc
Subject: (none)
Message-ID: <11834.314.forumexp@mts.rpi.edu>
Date: 2 Aug 90 05:04:00 GMT
Lines: 60


   >From article <260@oiscola.Columbia.NCR.COM>, by salmassr@oiscola.Columbia.NCR.C
   >
   > salmassr> Hi.  I always get confused between expanded and extended memory.
   > salmassr> Could anyone post or mail me a good explanation.
   >
   > salmassr> 1- What is the difference? (Technically & from a user point of view)
   > salmassr> 2- Why there are two kinds?
   > salmassr> 3- Which one you should use?
   > salmassr> 4- Can the computer use expanded and extended memory at the same time
   >
   > salmassr> and other related information that you can think of...
   >
   > Alright, but remember - you asked for this.
 
     Well, I have a difference, a correction, and an addition.
 
   > ?Only programs which are specifically written for expanded memory can
   > use it. This means that you can travel to the ends of the Earth and still not
   > find one that does (Nethack 3.0i is an example of a program which can use it.
   > I would mention others, but that would entail getting commercial).
 
     Ends of the earth, hardly, quite a few programs these days use extended
   memory.  I can name a half dozen off the top of my head with-out trying.
   The use of expanded memory is not that rare.
 
   >?While DOS is still on death row, however, you can get access to some
   > of Expanded memory through XMS drivers like HIMEM.SYS. Unfortunately
   > somebody appears to have cut the balls off HIMEM.SYS, and it only offers
   > 64K. Some software will use Extended memory anyway, by slipping into
   > protected mode while DOS isn't watching, and slipping out again.
 
     Umm, First, expanded memory is accessed via a EMS driver, not a XMS
   driver.  An XMS driver is used in conjunction with a extended memory.
   Secondly, someone did not "cut the balls off HIMEM.SYS".  Basically
   HIMEM.SYS is a very easy way of taking advantage of an addressing
   difference between an 8086 and a 80x86.  Namely, driving the A20 line
   high points to a valid area of memory.  Originally this pointed to no
   memory at all, so DOS was told to ignore it and most machines kept it low.
   This gets around that.  And that is why it only addresses 64K.
 
     The XMS specification is new, so I doubt yet there are many programs that
   use this method to access extended memory.  Most use one of two methods.
   One of these programs is VERY useful, that is RAMDRIVE.SYS.  This allows
   you to use the extended memory (or expanded, if you've loaded a EMS driver)
   as a ramdrive, a very useful thing to do.  It can speed things up (like
   batch files, or loading your COMSPEC from there).  Best of all, if you
   have DOS, you have this.  (At least in all the versions I've seen.)
 
     I agree that an operating system that works in protected mode is much
   nicer.  Windows 3.0 is cheap enough to be practical.  I like it alot
   personally.  Unix and OS/2 may be nice also, but I have no experience with
   them.
 
     Oh, and to answer your last question, yes a computer can
   use both extended and expanded at the same time.  Sometimes though
   it can be a pain to set up.  (Note the same memory can't be
   used for both, but the memory above 1meg can be partioned)
 
   Greg_d._Moore@mts.rpi.edu