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Programmable Storage Protection Mechanism

IP.com Disclosure Number: IPCOM000041182D
Original Publication Date: 1987-Nov-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Beukema, BL: AUTHOR [+4]

Abstract

This storage protection mechanism uses redundant address bits to check whether the storage address for a storage operation in a computer has been corrupted. Several otherwise unused high order bits of an address are duplicates of a section of the address.

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Programmable Storage Protection Mechanism

This storage protection mechanism uses redundant address bits to check whether the storage address for a storage operation in a computer has been corrupted. Several otherwise unused high order bits of an address are duplicates of a section of the address.

A number of bits in the address must be unused for this scheme to be applicable. The redundant storage protection mechanism works by copying a portion of the address bits that are used into the otherwise unused area.

The selection of the bits to be copied is the core of the mechanism. This method is meant for protection of main storage of the computer from malfunctioning input/output processors. Most modern computer systems use a page oriented structure which requires that input/output be done within pages in real storage. The most likely error in addresses from input/output processors is the incrementing or decrementing of the address outside of the intended page. Therefore, the bits immediately above those required for addressing within the page should be the ones copied to the redundant bit area.

For example, in a system with 2K pages, a 32 bit address, and three unused bits at the high order end of the address word, copy bits 18 through 20 of the 32 bit address (numbering bits starting with 0 being the most significant). These bits are the bits immediately above the 11 bits that are used to address within a 2K byte main storage page.

When the address is received in the main processor during a input/output request, the redundant bits must be compared to the bits they were copied from. If they match, the input/output request...