Path: utzoo!utgpu!water!watmath!clyde!ima!johnl
From: johnl@ima.ima.isc.com (John R. Levine)
Newsgroups: comp.arch
Subject: Re: Register Windows
Message-ID: <2768@ima.ima.isc.com>
Date: 13 Oct 88 05:08:22 GMT
References: <46500028@uxe.cso.uiuc.edu>
Reply-To: johnl@ima.UUCP (John R. Levine)
Distribution: na
Organization: Not much
Lines: 20

In article <46500028@uxe.cso.uiuc.edu> mcdonald@uxe.cso.uiuc.edu writes:
>What is a register window?

It's a little piece of Lexan in the chip package of a microprocessor that lets
you see into the machine's registers. Writers of optimizing compilers find
these windows invaluable for debugging and tuning object code. For example, in
case of register overflow you can see bits floating near the register that
overflowed. In case of register collisions, which all compiler writers will
agree are a big pain, if you examine the registers very closely with a
magnifying glass, you can usually see little scratches and dents where the
collision occurred.

Register windows are such a useful tool that it's a shame that the SPARC is
the only commercial chip that provides them, although even on the SPARC the
Lexan gets scratched after a few months, making them hard to see through. I
wish that quartz windows weren't so expensive, they last a lot longer.
-- 
John R. Levine, IECC, PO Box 349, Cambridge MA 02238-0349, +1 617 492 3869
{ bbn | think | decvax | harvard | yale }!ima!johnl, Levine@YALE.something
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