Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!mailrus!umix!nancy!eecae!super.upenn.edu!rutgers!bellcore!faline!thumper!ulysses!terminus!rolls!mtuxo!mtgzz!dam
From: dam@mtgzz.UUCP (XMRN40000[kvm]-d.a.morano)
Newsgroups: comp.arch
Subject: Re: Cache Terminology?
Message-ID: <3797@mtgzz.UUCP>
Date: 31 Mar 88 16:36:11 GMT
References: <3298@sequent.UUCP>
Organization: AT&T, Middletown NJ
Lines: 34
Keywords: cache, set
Summary: set has 2 blocks in 2-way set-associate

In article <3298@sequent.UUCP>, niven@sequent.UUCP (Kevin Joyce) writes:
> 
>  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

I have always used the definition that in the example of a 2-way 
set associate cache, that there are 2 blocks in every set and 
that the total number of sets is equal to half of the total 
number of blocks in the entire cache.  A 4-way set associative cache
would have 4 blocks in every set, etc.  Also, a 2-way set associative
cache would consists of two "groups", 4-way would have 4 groups, etc.
The entries in a group would consist of one block from each set in 
the cache.  The amount of associative parallelism (number of tag 
comparators) is directly related to the number of groups in the 
cache which is equal to the number of blocks in a set.  Sets can be 
numbered from the top starting at 0.  The set number is in fact 
usually the hardware address used to access the blocks in that set.
Groups can also be numbered (ie: group0, and group1 for 2-way) but
this numbering is usually not as useful or meaningful in the hardware
as the set number.  This definition seemed to be the one of choice, 
if not the only definition, in the literature before approximately 1982.  
Since then, caches have become much more common in microprocessor based 
computers and it seems that the definition of a set has also become 
much more ambiguous.

Also, in the last few years, the term "line" has become much more common
but can usually be assumed to refer to a cache block.

In the last few years, I have had to pick up the various cache definitions
of the speaker dynamically from the context of any discussion on caches.
Given a vote, I prefer Kevin's former definition as I have also stated 
above.  This seems to be the more traditional/historical definition.

Dave Morano	AT&T