Dynamic Data Reallocation in Bubble Memories

One major area of application of magnetic bubble technology is mass memory. 1 The potential advantages of bubbles over disk files and drums are: shorter access time, lower cost and power dissipation, * The contents of this paper were presented at the 1972 Intermag Conference by P. I. Bonyhard. 307 308 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1 9 7 3 reduced volume, and a higher degree of modularity. 2 Moreover, there are several operations which can be performed on the information in a bubble memory which cannot be performed by conventional magnetic recording. The purpose of this paper is to show that a magnetic bubble memory can function as a hierarchy, given certain operations which are not difficult to realize. The operations relevant to this paper are: transfer, instantaneous reversal of the direction of propagation, and removal of bubbles from a propagate channel while closing the gap left by them or creation of a gap while inserting new bubble information into the channel. Transfer of bubbles from one propagate channel to another already plays an important role in the design of bubble mass memories. 1,2 By a process of (i) propagating forward n cycles, («) removing bits from the channel and closing the gap, (in) propagating backward n cycles, and (iv) opening a gap and reinserting the bubbles, a permutation of the information in the channel is effected. It will be shown how a simple algorithm using one permutation element per propagate channel causes the memory to function as an integrated hierarchy.