Microsoft Word & (SCO) Unix 3.2

Darryl Richman darryl at
Tue Aug 22 23:22:44 AEST 1989

In article <1115 at ispi.UUCP> jbayer at ispi.UUCP (Jonathan Bayer) writes:
"darryl at (Darryl Richman) writes:
">Only Xenix 286 programs go through the x286emul environment emulator
">program.  Xenix 386 programs execute natively.  286 programs vary in
">speed, but are often faster than under either Xenix 286 or Xenix 386
">because the memory management is significantly faster under x286emul.
"How is the memory management faster in emulation mode than in native 386 mode?

The emulator actually gets memory a 64k segment at a time and doles it
out as the XENIX program sbrks for it.  Requests for memory that the
environment emulator already has never go into the kernel and only take
a few instructions to map into the 286 program's address space.  I
don't recall the exact numbers, but frequent requests for small amounts
of memory can be an order of magnitude faster.  Of course, when the
program asks for 64k segments, things are close to equal.  They are
still faster than under 386 XENIX because the emulator knows that it is
running a 286 XENIX program, but XENIX memory management code must
check this at each place where handling the memory request must be
different between a 286 and a 386.

PLEASE NOTE:  when I speak of 386 XENIX, I'm talking about version 2.3
or earlier.  SCO XENIX V.3.2 is the same code base as UNIX V.3.2.  I am
not attempting to compare current products.

		--Darryl Richman
Copyright (c) 1989 Darryl Richman    The views expressed are the author's alone
darryl at 		      INTERACTIVE Systems Corp.-A Kodak Company
 "For every problem, there is a solution that is simple, elegant, and wrong."
	-- H. L. Mencken

More information about the Comp.unix.i386 mailing list