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Paging Apparatus for Data Storage Hierarchy System

IP.com Disclosure Number: IPCOM000083766D
Original Publication Date: 1975-Jul-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

East, DG: AUTHOR

Abstract

Data in a storage system is often organized in units that are called pages, and pages can be exchanged between the main store of the system and a larger backing store as programs progress through different pages, and as additional storage space is needed in the main store. When some page must be selected to be removed from main store to make space for a new page, it is common to select a page that has not recently been accessed.

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Paging Apparatus for Data Storage Hierarchy System

Data in a storage system is often organized in units that are called pages, and pages can be exchanged between the main store of the system and a larger backing store as programs progress through different pages, and as additional storage space is needed in the main store. When some page must be selected to be removed from main store to make space for a new page, it is common to select a page that has not recently been accessed.

The store in the drawing has a word location for each page of a main store, not shown. This word location holds a value that signifies the age of the associated page. The initial value, called a latency value, is loaded into a word location when the associated page is first entered into the main store and each time the page is accessed. Thus, the most recently used page has the latency value.

When a page is accessed, a scan of the store is started to read each word location, check its value, and decrement the word and restore it in its location. The drawing shows the decrementing components for the representative four low-order bits of the word.

Bits 0, 1 and 2 are transposed to become bits 1, 2, and 3 of the new stored value. New bit 0 is formed as the exclusive OR function of original bits 2 and 3. thus, the latency value is 1000, the second value becomes 0100 and the third value is 0010, as a shift operation is produced by the transposition of values and the exclusive OR circuit receiv...