Browse Prior Art Database

System for Handling Engineering Changes

IP.com Disclosure Number: IPCOM000081394D
Original Publication Date: 1974-May-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

Craft, DJ: AUTHOR

Abstract

Since the bit densities of read-only storage (ROS) units are in general higher than those of read/write storage and moreover the power dissipation of read-only stores is normally lower, it is attractive to put as much as possible of a system microprogram into read-only storage. However, circumstances do arise, for example, where engineering changes (ECs) are introduced after a machine has been manufactured which require the microprogram to be modified. When all the microprogram is stored in read-only storage, substantial hardware alteration then becomes necessary.

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System for Handling Engineering Changes

Since the bit densities of read-only storage (ROS) units are in general higher than those of read/write storage and moreover the power dissipation of read-only stores is normally lower, it is attractive to put as much as possible of a system microprogram into read-only storage. However, circumstances do arise, for example, where engineering changes (ECs) are introduced after a machine has been manufactured which require the microprogram to be modified. When all the microprogram is stored in read-only storage, substantial hardware alteration then becomes necessary.

The figures show an arrangement for overcoming this problem. An engineering change storage module (Fig. 1) consists of a read/write store and a random access memory, together with a small associative store. The read/write store is arranged like any other random access memory module and may be addressed by the system, just as any other normal extension to the memory. The associative store is arranged to search over all bits of the address presented on the address bus, whether the address relates to the engineering change storage module or not. If an address is presented which matches that contained in one of the search words of the associative array, then the EC storage module activates its "disable" output, and drives the data contained in the corresponding Read Word of the associative array out on to the storage data bus.

Fig. 2 shows part of a computer system with the EC storage m...