Path: utzoo!mnetor!uunet!tektronix!sequent!niven
From: niven@sequent.UUCP (Kevin Joyce)
Newsgroups: comp.arch
Subject: Cache Terminology?
Message-ID: <3298@sequent.UUCP>
Date: 29 Mar 88 23:44:38 GMT
Organization: Sequent Computer Systems, Beaverton, OR
Lines: 21
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. Also Assume Block Size And Line Size Are The
Same . In This Case 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. Implementation Of This Architecture Might Involve
Two Banks Of Memory Chips. Sets, By The This Definition, Are Divided Between
These Banks. One Of The Two Blocks Of Each Set Is In Either Bank. Both Banks
Are Searched Simultaneously For An Data Access. 

The Alternate Definition, I Have Come Across For Sets, Is In Referring To Each 
Of The Memory Banks Described Above 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 ? It Certainly
Makes No Difference To The Hardware How Things Are Named.

sequent!niven