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Reading Storage Protection Bits

IP.com Disclosure Number: IPCOM000078114D
Original Publication Date: 1972-Nov-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Price, R: AUTHOR

Abstract

This is a method for detecting the storage protection bits in machines, in which no instructions are provided for reading these bits. This method consists in replacing or attempting to replace the contents of the word by the same value. If there is a protection bit, the attempt causes an interruption which is analyzed.

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Reading Storage Protection Bits

This is a method for detecting the storage protection bits in machines, in which no instructions are provided for reading these bits. This method consists in replacing or attempting to replace the contents of the word by the same value. If there is a protection bit, the attempt causes an interruption which is analyzed.

A computer such as the IBM System I800 process control computer has a storage protection bit associated with each word in store. No instruction is provided for reading this bit. Still, when a program or data is transferred from a storage zone to another one, it is necessary to read the storage protection bit in order to transfer its value.

The present method provides a mechanism for reading the storage protection bit at address A.

For this purpose, the storage protection violation interruption routine is modified to detect a deliberate violation. On detection, a bit B is set to 1 and the interruption routine terminates with no other effect, i.e. without calling the error programs.

To read the storage protection bit at address A, the bit B is reset to 0, the contents of A is read and an attempt is made to write it back at the same address. If the storage protection bit is equal to 0, the write operation is normally effected and B remains equal to 0. If the storage protection bit is equal to 1, the interruption occurs, and the interruption routine sets B to 1. In both cases, the value of B is equal to the value of the...