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Browse Prior Art Database

Pseudo Two-way Associative Array

IP.com Disclosure Number: IPCOM000115366D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 65K

Publishing Venue

IBM

Related People

Imming, KC: AUTHOR [+2]

Abstract

Disclosed is a hardware implementation of a two-way set-associative Translate Lookaside Buffer (TLB) using unbalanced classes to approximate two-way performance with reduced circuit area and reduced circuit delay.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 57% of the total text.

Pseudo Two-way Associative Array

      Disclosed is a hardware implementation of a two-way
set-associative Translate Lookaside Buffer (TLB) using unbalanced
classes to approximate two-way performance with reduced circuit area
and reduced circuit delay.

      Two-way set-associative caches improve performance by
preventing thrashing when more than one address from a synonym set is
accessed frequently.  This is implemented by accessing two arrays in
parallel using a "set" address derived from the complete address.
This "set" may be derived by simply selecting a bit field or by a
more complicated hash algorithm.  The outputs from these two arrays
are compared, again in parallel, to the remainder of the full address
to determine if the data associated with this address is contained in
the cache (i.e., a hit).

      Larger arrays provide more associativity classes, resulting in
higher hit rates and thus better performance.  Set associativity
provides increased performance by overcoming the thrashing that
occurs when multiple items belonging to the same set are needed
simultaneously.  The problem with these larger arrays is that they
require more circuit area and longer access times, resulting in
increased circuit delays.  In the case of the TLB, this increases the
logic delay in the critical path of translating virtual addresses.

      In the past, set-associative arrays have been considered to be
symmetrical.  Both sets are the same size and the set sel...