Arthur V. Pohm

Cost/performance perspectives of paging with electronic and electromechanical backing stores

An analysis is made of the cost/performance effectiveness of virtual memory systems employing paging disks or drums and those employing electronic backing stores such as charge coupled devices (CCD), MOS shift registers, or bubbles. The analysis is based on a multiprogrammed job stream and a simplified queuing model employing page-fault rates suitable for a variety of multiprogrammed environments. Smaller memory systems and single job programming are also considered. It is shown that memory access plus page transfer time is a critical parameter, in addition to cost. Curves are generated for a variety of job environments in which the cost/performance effectiveness of two-level memory hierarchies employing electronic backing stores is compared to that of systems employing paging drums. Competitive prices per bit are determined for a number of system environments. The analysis clearly demonstrates that in many problem environments, the electronic backing store will replace the traditional paging drum or disk if the cost per bit is significanfly less than the main memory cost per bit as projected. Disk and tape memories can be expected to continue as the dominant memories for bulk storage in the near future because of their already small and diminishing costs per bit.

The cost and performance tradeoffs of buffered memories

An analysis of the performance enhancement achieved and the incremental costs accrued in buffering (using a cache memory) memory systems is made. Buffering is found to be cost-effective even for minicomputer memories. The study indicates that the flagged registered swap algorithm is superior to three other common algorithms used. It is shown that when jobs are switched, a substantial number of memory requests are required before the buffer fills and gives a high hit ratio. It is also shown that individuaIly buffered main-memory modules can be interleaved to achieve very high system performance.

A New Approach to Resistor-Transistor-Tunnel-Diode Nanosecond Logic

A transistor amplifier with nonlinear tunnel-diode or backward-diode feedback is described for use as a resistor-coupled threshold logic circuit or general purpose switch. The tunnel-diode feedback serves to virtually eliminate saturation and prevent cutoff thus allowing the high gain-bandwidth products of epitaxial switching transistors to be utilized at all times during switching. Switching plus delay times as low as 2 nsec have been observed with a fan in and fan out of three. Ring oscillator experiments show that delays per stage from 2 to 5 nsec are easily obtained with logical gains of two or three. The input impedance of the network is 3 to 12 ohms leading to a very practical threshold network. The particular logic decision is determined only by the bias current. Tolerance calculations are presented that indicate component requirements will not be severe. The peak current is not a critical parameter and can easily vary 100 per cent. Due to the quantizing effect of the tunnel-diode feedback, circuits with fan ins and fan outs of three would operate satisfactorily under worst case conditions with 2 per cent resistors and mild restrictions on the transistor and diode parameters. By adding backward diodes in series with the input resistors the tolerance requirements can be relaxed to 10 per cent resistors and slight restrictions on the diodes or transistor parameters. By using backward diodes the fan in and fan out can be substantially increased with little loss in speed.

Tutorial Series 13 Computer Memory Systems

Because there are no very fast, cheap, reliable memories on the technological horizon, memory hierarchies will continue to play a key role in computer system design.

Electronic Replacements for Head-per-Track Drums or Disks

Recently, three types of memories have been proposed as possible main memory extensions and replacements for head per track disks or drums; these are CCD, bubble, and BEAMOS memories.1,2,3The extent to which these memories come into widespread use will depend on such factors as cost, performance, reliability, maintainability and profitability. In this paper, potential areas of application for these memories are examined and some of the conditions which must be met for the memories to be economically attractive are determined for systems employing both a single job stream and multiprogrammed job streams.

Magnetic Film Scratch-Pad Memories

An economic comparison has been made between fully integrated scratch-pad memories and thin magnetic-film scratch-pad memories on the basis of assumed component costs. On this basis, magnetic film memories are more expensive than fully integrated memories for very small memories, as expected. In terms of the assumptions made, the economic crossover as a function of memory size between the two memory types lies between 500 and 10 000 bits of storage. Two sample thin-film scratch-pad memory designs are given which have comparatively simple electronic circuitry using integrated circuit power supplies. This electronic circuitry also is amenable to integrated or hybrid circuit implementation.

Top-Down System Design A Tutorial Overview

In this introduction to hardware design topics within the ongoing tutorial series, the editors accent the essential link between software and hardware design.

High Speed Magnetoresistive Memories

In order for a new memory technology to be successful in the general commercial market, it needs to not only provide additional features, but it also must be cost effective. For the present day computer hardware environment, this requires that the technology exploit the billions of dollars that have been invested in silicon technology. It also requires that the new technology have the capability of scaling as the minimum feature size in production lithography continues to diminish. Table 10.1 shows the continuing reduction in feature size for integrated circuits and the anticipated reduction in size in the future as projected by the Semiconductor Research Corporation (SRC).