Wilhelm Anacker

Potential of superconductive josephson tunneling technology for ultrahigh performance memories and processors

The potential of a new technology, based on the superconducting Josephson tunneling effect, has been assessed for use in high-speed computer systems. Josephson tunneling circuits for memory and logic functions can be switched at sub-nanosecond delay, do not require standby power, and dissipate extremely low energy, typically less than 10-13joule during fast switching operation. High-speed circuits with high packing densities, not limited by power dissipation problems, can therefore be expected. Low thermal noise at cryogenic temperatures ensures reliable operation despite the low energy switching signal. Practically lossless signal transmission via superconducting lines can be exploited for high-speed operation even when sizeable memory and logic modules are assembled. Two random access memory modules have been designed on the basis of single device experiments. Operational characteristics leading to the conclusion that 30 Mbit capacity, less than 1 watt refrigeration requirement (at 3.6° K) and cycle times of 40 ns (in one case) and 15 ns (in the second case), can be achieved are presented.

Performance Evaluation of Computing Systems with Memory Hierarchies

Data transfers in computing systems with memory hierarchies usually prolong computing time and, consequently, cause degradation of system performance. A method to determine data processing rates and the relative utilization of memories for various system configurations under a variety of program loads is presented. According to this method, a program-independent ultimate data processing rate is derived from characteristics of the processor and the fastest random access memory of the system, and degradation factors are determined by combining statistics of the data flow of actual programs and hardware parameters of the processor and all memories. The statistics of data flow in the memory hierarchy are obtained by analyzing a number of recorded address traces of executed programs. The method presented permits quick evaluation of system performance for arbitrary time periods and for maximum and minimum concurrence of operation of processors and memories.

Possible uses of charge-transfer devices and magnetic-domain devices in memory hierarchies

Characteristics of magnetic-domain device (MDD) and charge-transfer device (CTD) memory modules which appear technically feasible and desirable for use in computer applications are derived. The possible uses of these memories in the memory and storage subsystems of computers are discussed. The concept and measures of performance of memory hierarchies is outlined and possible improvements by incorporation of MDD and/or CTD memories in hierarchies employing conventional memories are addressed. A scheme comprising two hierarchy levels on the same chip is evaluated by using the derived performance measures.

Josephson tunneling devices: a new technology with potential for high-performance computers

Superconducting thin film devices which exploit the Josephson effect and Giaever type tunneling have been observed to switch very fast while dissipating extremely little power. They show, therefore, good promise for high-performance computer circuits since the low power dissipation permits dense packaging with attendant short intercircuit signal delays, a prerequisite for effective utilization of fast switching circuits.

Superconducting memories employing Josephson devices

Experimental superconducting Josephson devices being investigated for use in digital logic and memory circuits have been demonstrated to switch in the 10 to 100 picosecond (1 picosecond = 10-12 sec) range. Projections based on the operation of individual logic circuits indicate that they may surpass semiconductor circuits in very high performance CPUs. This potential is based on the fact that these circuits dissipate extremely little energy, on the order of 10 to 1000 attojoules (attojoule = 10-18 joule), while operating with subnanosecond delays. It should, therefore, be possible to package Josephson devices very densely and interconnect them by properly terminated superconducting transmission lines so that the fast switching speed of individual circuits is retained throughout large logic networks.