Path: utzoo!mnetor!uunet!husc6!mailrus!ames!oliveb!sun!joe!petolino
From: petolino%joe@Sun.COM (Joe Petolino)
Newsgroups: comp.arch
Subject: Re: Cache Terminology?
Message-ID: <47555@sun.uucp>
Date: 30 Mar 88 17:32:13 GMT
References: <3298@sequent.UUCP>
Sender: news@sun.uucp
Reply-To: petolino@sun.UUCP (Joe Petolino)
Organization: Sun Microsystems, Mountain View
Lines: 31
Keywords: cache, set

> It Has Come To My Attention That There Are Two Quite Different Definitions
>For The Word Set In Cache Architecture Circles.
>For Simplicity Assume A Two- Way Set Associative Architecture. . . .
>One Definition Of Set Is That It Refers Any 2 Blocks Of 
>Memory, Both Of Which Are Searched Associatively For A Given Data Word. In
>This Case The Set Size Is Two And The Number Of Sets Is Half The Number Of
>Blocks In The Entire Cache. . . .
>The Alternate Definition [Refer] To Each 
>Of The Memory Banks  . . . As A Set (Eg Set0 And Set1). With This 
>Latter Definition The Set Size Is Now The Number Of Blocks In That Bank Of 
>Memory, And The Number Of Sets Is Two. 
>
>So Which Is The Industry Accepted Standard? Does Anyone Care?

Yes, I Care.  I Wish People Would Stop Using The Second Definition.

Uppercase aside, this is a particularly nasty problem, since, whichever
definition you choose, there is no generally-accepted name for the other
thing.  The first definition has obvious mathematical roots (the cache is not
truly an 'associative' memory, but, on a given access, a *subset* of the
cache is selected and its operation is associative *within that set*, i.e.,
it is 'set-associative').  I have always thought that the use of the word
'set' to mean 'memory bank' was perpetrated by people who wanted to lend an
air of academic authority to their speech but didn't quite get it right.  It
does seem fairly widespread in the industry, however, mainly because the
thing they are referring to (the 'memory bank') is a very basic and useful
concept for hardware designers to talk about, and there isn't any other good
name for it.  I usually call this thing an 'associativity', but that's too
cumbersome (seven syllables!).  Any other suggestions?

-Joe