An 8 MBYTE magnetic bubble memory

This paper reports design and operation of a large capacity magnetic bubble memory developed for an electronic switching system to replace a magnetic drum memory. Eighty 64 kbit magnetic bubble memory chips, including redundant chips, compose a 0.5 Mbyte memory unit with a multi-chip packaging approach. Peripheral circuits, magnetic structures and other miscellaneous packaging parts are shared by as many chips as possible in the memory unit to minimize the amount of hardware. A controller manages a maximum of 16 memory units, which realizes a memory system with 8 Mbyte storage capacity. Performance enhancement with minimum controller hardware has been accomplished by having one controller manage data search operations on bubble chips of 8 different memory units in a multiplexing mode. An efficient fault tolerance method has been developed combining redundant minor loops with redundant chips, so that effective device production yield is about 20% greater than with conventional methods. These factors result in magnetic bubble memory equipment with higher performance, lower bit cost, and better maintainability than conventional magnetic drum memories.