Dynamic data reallocation in bubble memories

Abstract

Bubble technology offers several operations that have no equivalents in technologies based on magnetic recording. Examples of such operations are: transfer, reversal of the direction of propagation, and opening and closing of gaps in the data stream. This paper∗ shows how such operations can be used to dynamically reallocate data in the bubble memory, causing it to become an integrated memory hierarchy. A considerable improvement in performance results. A model is presented which relates the bubble memory with dynamic reallocation to stack processing, a technique used in the evaluation of memory hierarchies. With the aid of this model it becomes possible to calculate the performance of the bubble memory using published data derived from the traces of selected typical programs. Memory design is optimized for the execution of such programs. Design parameters are proposed for a 2-Mb bubble memory with 128 detectors which, in the execution of the type of program for which data were available, requires an average of only 8.8 shifts for access and an average of 12.1 shifts per memory cycle. If bubbles are propagated at a rate of 1 MHz, the average access and cycle times for this memory become 8.8 µs and 12.1 µs, respectively. Such performance, in conjunction with the low cost per bit offered by bubble technology, is expected to have a major impact. The performance of this memory, when operated in conjunction with a faster buffer, is also calculated. The use of a 64-kb buffer is shown to reduce the average number of shifts for access to 1.05, and the average number of shifts per cycle to 1.9.