Browse Prior Art Database

Read Only Store Alteration

IP.com Disclosure Number: IPCOM000081210D
Original Publication Date: 1974-Apr-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Hudson, RR: AUTHOR

Abstract

Read-Only Storage (ROS) instructions or data is altered without physically changing the ROS elements. Storage address register 10 simultaneously addresses ROS 15 and associative storage 20. Associative storage 20 is a read/write type of storage loadable from main storage, disk storage, etc., not shown. It is substantially smaller than ROS 15; however, each storage position therein contains an address plus modifier or mask data bits. By this arrangement, whenever the address in register 10 selects a ROS storage position which is to be altered because it is in error as to content or is physically defective, the contents of that storage position are modified by exclusive OR circuits 30 as the modifier data bits associated with the address in storage 20 are simultaneously applied thereto.

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Read Only Store Alteration

Read-Only Storage (ROS) instructions or data is altered without physically changing the ROS elements. Storage address register 10 simultaneously addresses ROS 15 and associative storage 20. Associative storage 20 is a read/write type of storage loadable from main storage, disk storage, etc., not shown. It is substantially smaller than ROS 15; however, each storage position therein contains an address plus modifier or mask data bits. By this arrangement, whenever the address in register 10 selects a ROS storage position which is to be altered because it is in error as to content or is physically defective, the contents of that storage position are modified by exclusive OR circuits 30 as the modifier data bits associated with the address in storage 20 are simultaneously applied thereto. The modified data passes from exclusive OR circuits 30 into register 35.

This technique for selectively modifying the contents of ROS not only make it possible in effect to repair defective storage positions, it enables instruction data to be changed or substituted. For example, a program could load storage 20 with an instruction for changing the instruction in ROS 15. The program could also load storage 20 with an instruction to be used instead of an instruction from ROS 15, if there are any unused storage positions in ROS 15. With this latter arrangement, the program would branch to the address of the unused ROS storage position and then return to the ad...