Browse Prior Art Database

Buffer Page Replacement

IP.com Disclosure Number: IPCOM000079948D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Mitchell, GR: AUTHOR

Abstract

The most recently used pages in a fast buffer store are preserved therein and any one of the other pages (least used) is arbitrarily replaced.

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Buffer Page Replacement

The most recently used pages in a fast buffer store are preserved therein and any one of the other pages (least used) is arbitrarily replaced.

The fast buffer store 10 is illustrated in Fig. 1 as having sixteen pages of storage. Page usage is generally random; however, the most recently used pages have the highest probability of reusage. Thus, only the most recently used pages are kept track of and the remaining pages are all candidates for replacement.

As a page is accessed in buffer 10, a bit associated with that page is set on in one of five sixteen-position registers 20 addressed by counter 25, which has one position for each of the registers 20. If the bit associated with the selected page was already set on, counter 25 is not incremented. However, if a different bit in the addressed register had been on, it is turned off and counter 25 is incremented by counter advance logic 30. The outputs of registers 20 are logically OR'ed together by accumulator/comparator 35, to provide logic 30 with signals for controlling the advancement of counter 25 and to provide signals for page replacement.

The arbitrary selection of the page to be replaced is accomplished with random page selector 40, which is a free-running shift ring with only a single bit turned on. The outputs of random page selector 40 are applied to accumulator/comparator 35. If the bit position selected by 40 matches one that is on in any of the registers 20, as determined by accu...