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Path: utzoo!linus!decvax!cca!johnl
From: johnl@cca.UUCP
Newsgroups: net.micro.pc
Subject: Re: Re: 286 slower than 8086? - (nf)
Message-ID: <423@ima.UUCP>
Date: Sun, 30-Sep-84 23:40:20 EDT
Article-I.D.: ima.423
Posted: Sun Sep 30 23:40:20 1984
Date-Received: Tue, 2-Oct-84 05:41:45 EDT
Lines: 12

#R:sun:-170700:ima:12700002:000:498
ima!johnl    Sep 30 15:11:00 1984

It's true.  Loading a 286 segment register in protected mode is very slow.
According to my handy 286 manual, "MOV ES,AX" would take 2 cycles in real
(8086-like) mode but 17 cycles in protected mode.  That's because it has
to load four bytes out of the descriptor table to find out what the new
contents of the segment register actually mean.  Looks like a big loss if you're
trying to simulate a linear address space 'cause your data doesn't naturally
fall into 64K chunks.

John Levine, ima!johnl