Special Tutorial: The Organization of Electronic Cyclic Memories

Cyclic memories are memories in which data rotate cyclically past a read/write port. The most common cyclic memories in use today are mechanical drums and fixed-head disks. In the past, small electronic cyclic memories have been made from MOS technology; more recently they have been made from charge-coupled devices and magnetic bubbles. Because of advances in integrated technology, large electronic cyclic memories that might be replacements for drum and disk memories are likely to become available. Whereas it is difficult to predict what technology will eventually emerge for electronic auxiliary memories, present projections suggest that cyclically organized memories based upon magnetic bubbles or charge-coupled devices are potential candidates. The disadvantage of cyclic organization is that access time due to memory latency may be excessive. The problem we investigate in this paper is how to modify electronic cyclic memories in relatively minor and inexpensive ways so as to decrease rotational latency in a system environment.