Subject: Re: 2 megs or not 2 megs? :-)
From: jryan7@pop.site1.csi.com (Jared Ryan)
Reply-To: jryan7@csi.com
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Date: Sun, 22 Mar 1998 15:23:42 -0500
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In article <1d65pdf.cx3nhq14a0pxsN@host5-99-48-182.btinternet.com>, 
Aq@btinternet.com says...

>My 286 has 2 megs of XMS[1], not EMS (since you can't get EMS on a 286).

A 286 can access either eXtended or Expanded memory.  A 286 can access up to 
16Mb including the first 1Mb, which includes the DOS 640K and the 384K 
normally reserved for ROMs and the like.

Expanded memory can only be addressed with a memory manager, a driver that's 
loaded after DOS.  The Lotus-Intel-Microsoft (LIM) EMS 4.0 spec became 
standard.  Systems so equipped can have up to 32Mb of EMS, in theory.

eXtended memory can only be accessed with the 286 in protected mode.  
Protected mode on the 286 is somewhat crippled; Intel designed no method for 
knocking the system *out* of protected mode.  To switch back to real mode, the 
system needs to be reset - which some programs actually do, using a spare pin 
on the keyboard interface chip.  This is all related to the A20 line you 
sometimes see mentioned.
-- 
 - Jared Ryan [jryan7@csi.com]
http://surf.to/el-camino/ ~~~~~~~ ICQ # 8457412
"American by birth, Texan by the grace of God."

