Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site peora.UUCP
Path: utzoo!linus!decvax!bellcore!petrus!sabre!zeta!epsilon!gamma!ulysses!mhuxr!mhuxt!houxm!vax135!petsd!peora!jer
From: jer@peora.UUCP (J. Eric Roskos)
Newsgroups: net.arch
Subject: Re: Tagged architectures
Message-ID: <1699@peora.UUCP>
Date: Mon, 7-Oct-85 16:51:35 EDT
Article-I.D.: peora.1699
Posted: Mon Oct  7 16:51:35 1985
Date-Received: Thu, 10-Oct-85 06:49:11 EDT
References: <796@kuling.UUCP> <1713@orca.UUCP> <1599@peora.UUCP>
Organization: Perkin-Elmer SDC, Orlando, Fl.
Lines: 19
Keywords: tags, memory protection

> I don't understand why anyone would want to use tags for read/write
> protection.  Whether you can read/write a memory location is either
> determined by your page table entry for the current virtual space or
> by some capability you possess.

For one thing, because you can then "read/write protect" memory in much
smaller units... but the tags are for other things than that, also, e.g.,
to show the type of the datum, perhaps; or to show whether it is "present";
or the access level required in order to be able to read or write it; etc.

A "capability" in this sense could be thought of as just a set of tags off
somewhere else in memory, along with a pointer to the object the tags are
for...
-- 
Shyy-Anzr:  J. Eric Roskos
UUCP: Ofc:  ..!{decvax,ucbvax,ihnp4}!vax135!petsd!peora!jer
     Home:  ..!{decvax,ucbvax,ihnp4}!vax135!petsd!peora!jerpc!jer
  US Mail:  MS 795; Perkin-Elmer SDC;
	    2486 Sand Lake Road, Orlando, FL 32809-7642