Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!ucla-cs!fan
From: fan@CS.UCLA.EDU
Newsgroups: comp.sys.intel
Subject: 286 vs 386 (should we buy an AT now?)
Message-ID: <5634@shemp.UCLA.EDU>
Date: Wed, 22-Apr-87 09:44:52 EST
Article-I.D.: shemp.5634
Posted: Wed Apr 22 09:44:52 1987
Date-Received: Fri, 24-Apr-87 01:10:45 EST
Sender: root@CS.UCLA.EDU
Reply-To: fan@CS.UCLA.EDU (Roy Fan)
Distribution: comp
Organization: UCLA Computer Science Department
Lines: 20

-------------------

	On the 286's selector:  bit 0-1 is RPL, bit 2 is TI, and bit
3-15 are the index into the descriptor table.  Now we are going to use
protected mode to run some programs for the IBM PC.  Could it be that some
programs have to be rewritten because they use the fact that on the
8086/8088, effective address = (SEGMENT << 4 + OFFSET).

	Furthermore, would SideKick or any other TSR (Terminate but
Stay Resident) utility work?  If the TSR program redirects
some interrupt vectors to itself by modifying the interrupt vector,
wouldn't that generate a trap on the 286's protected mode?  Besides,
286 protected mode doesn't use interrupt vectors any more, since IDT
is now used.

	On the 386, there is the virtual 8086 mode.  Presumably
programs could run unmodified on the 386.  Now the question is:
should we buy an AT now or should we wait and buy the 386 machines?

Roy Fan