Browse Prior Art Database

Partial Directory Lookaside Table Deletion

IP.com Disclosure Number: IPCOM000080571D
Original Publication Date: 1974-Jan-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Gannon, PM: AUTHOR [+2]

Abstract

This scheme permits degraded but continued operation of Directory Lookaside Tables (DLAT's) in virtual memory systems.

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Partial Directory Lookaside Table Deletion

This scheme permits degraded but continued operation of Directory Lookaside Tables (DLAT's) in virtual memory systems.

In a virtual memory system virtual addresses are translated to real addresses using sets of translation tables. Lookaside tables are used for storing previously translated addresses, so that they may be reused when the same virtual address is requested. This, of course, shortens the obtaining of data when required by virtual address, since the translation process is short-circuited. Previously there were two ways of operating a virtual address memory system when an error was found to exist in such a lookaside table. One way was to freeze the lookaside table. This inhibited further updating of the data within the table. The second way was to completely disable the lookaside table. Both these previous methods resulted in serious degradation of the virtual memory system.

Here it is proposed that the lookaside table 10 be divided into two parts 12 and 14 as some already are. Then when an error occurs, the half containing the error could be removed from operation and the other half to be used in the usual manner. For example, an error which is detected in part 12 would automatically result in no updates of part 12. All further updates would be forced into part 14. In this way, only a 3 - 5% degradation in system operation occurs and the high- speed buffer continues in use. If both parts 12 and 14 were in erro...