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Armstrong (1965) emphasizes that, in general, no lenses are required and the reconstructed image can be magnified or demagnified as desired.6.60
As of early 1969, however, the question has been raised that holograms may be already outdated.6.61 A new wavefront reconstruction device - the kinoform-is a computer-generated device intended to provide a reconstructed three-dimensional image of various objects with greater efficiency than is available with holographic procedures (Lesem et al., 1969),6.62
In addition to the use of holographic techniques for three-dimensional image storage and recall (including rotation 6.63), these techniques are also being explored for bandwidth compression in pictorial data storage 6.64 the production of highly magnified images,6.65 and other novel applications.6.66 In particular, it has been claimed that holographic techniques offer a new potential for high-quality-image capture in regions of the electromagnetic spectrum extending beyond those that have been achieved by optical recording techniques in the the region of visible light.6.67
Then it has been reported that "General Electric's Advanced Development Laboratories, Schenectady, build a laser holograph reader- a device capable of reading characters in several ways. It can detect a single object out of many without scanning, or if scanning is used, can recognize up to 100 different characters. The holographic reader is said to show wide tolerance for variations in type font and is expected to find applications in the computer field." (Veaner, 1966, p. 208.)
Laser and holographic techniques in combination are also being investigated for high density digital data storage, for example, at the Bell Telephone Laboratories, 6.68 at Carson Laboratories,6.69 and at IBM.6.70
Some special areas where advanced optoelectronic techniques and improved materials or storage media continue to be needed include "certain operations, such as two-dimensional spatial filtering (that) can be readily accomplished, in principle, with coherent light optics. Problems under consideration include: the effect of film-grain noise on the performance of a coherent optical system; the relation of film thickness and exposure; techniques for the making of spatial filters; and the effect on the reconstructed picture of various operations (such as sampling, quantization, noise addition) upon the hologram. (Quarterly Progress Report No. 80, Research Laboratory for Electronics, M.I.T., 221 (1966).)
McCamy (1967) reports recent extension of previous R & D investigations into fading and aging blemishes in conventional microforms to the effect of formation of such blemishes on information stored by means of holograms. It is to be noted further that certain types of holograms have an important immunity to dust and scratches.6.71
Possibilities for a holographic read-only store are under investigation at IBM (Gamblin, 1968), RCA (Viklomerson et al., 1968), and at the U.S. Army
Electronics Command, Fort Monmouth. In particular, "it is intended that a hologram of a binary data array would constitute the card-like removable media. Upon insertion into the memory read unit, the hologram would continuously focus a real image on the data onto a photodetector matrix. Such an arrangement can permit electronic random access to the information within the array while eliminating the stringent optical requirements on the detectors involved." (Chapman and Fisher, 1967, p. 372),6.72 Other R & D possibilities of interest include experimentation with acoustic 6.73 and computer-generated holograms.6.74 The computer generation of holographic or kinoform recordings is thus another development in this area of advanced technology. For example, digital holograms may be generated by computer simulation of wave fronts that would emanate from particular optical elements arranged in specific geometrical relationships (Hirsch et al., 1968).6 6.75 An interesting area of investigation is that of computer synthesis of holograms of three-dimensional objects which do not, in fact, physically exist.6.76
6.1.4. Other Optoelectronic Considerations
In general, it is emphasized that increasing interest has been evident in the use of optoelectronic techniques for both computer and memory design for a wide variety of reasons. Scarrott (1965) and Chapman and Fisher (1967) point to the high densities achievable with photographic media. 6.77 Reich and Dorion (1965) suggests a photochromic film memory plane, 2" x 2", with 645 subarrays individually accessible and a total capacity, assuming only 50 percent utilization of the film area, of better than 12 million bits.6.78 Potentially, then, many of these techniques promise significant advances in data storage, in logic and processing circuitry, in alternative communications means, in computing or access speed, and in data collection with respect to two- and three-dimensional object representation, including spatial filtering.6.79
Bonin and Baird (1965, p. 100) list other applications of optoelectronic techniques for tape and card readers, position indicators, and recognition equipment. In addition, important new areas will include use in communication and transmission systems. Here it is noted that optical techniques as applied to advanced communication systems planning relate also to continuing theoretical investigations. Thus, "preliminary studies of communication systems employing optical frequencies have indicated three topics to which the concepts and techniques of modern communication theory may most profitably by addressed. They are (i) the import of quantum electrodynamics for the characteristics of efficient communication systems, (ii) the relevant description of device noise as it affects the performance of communication systems, and (iii) the statistical characterization of the atmosphere as a propagation channel at optical frequencies." (Quarterly Progress
Report No. 80, Research Laboratory for Electronics, M.I.T. 178 (1966).)
For use as computer logical elements, somewhat less attention has been paid to date to the optoelectronic techniques. However, Ring et al. (1965, p. 33) point out that "it well may be that optical devices which do not appear at all suitable as binary computer elements may be very effective computing devices in the context of some other logic structure (e.g., majority logic, multivalued logics)."
Reimann adds: "With the advent of the laser, efficient light-emitting diodes, and high-speed photodetectors, interest in the application of higher speed opto-electronic circuits to digital logic has increased. . . . We may in the future expect to see opto-electronic circuits which will combine laser amplifiers with other high-speed semiconductor devices." (1965, p. 248).
Then we note that optoelectronic techniques may also be used to attack some of the problems that increasingly plague the circuit designer.6.80 Possibilities for circumventing interconnection limitations which become more severe as physical area per component is reduced are also stressed by Reimann (1965, p. 247). He states: "The possibility of signal connection between parts of the system without electrical or actual physical contacts are very attractive for integrated circuit techniques. With optical signals, a totally new approach to the interconnection of digital devices is possible."
Optoelectronic techniques as applied to the problems of large, inexpensive memories are not only promising as such,6.81 they also may be used to attack the noise problems still posed by integrated circuits.6 6.82 Thus Merryman savs "one attractive property of optoelectronic devices is their potential for isolation; they can get rid of the noise that is generated when two subsystems are coupled. The noise problem is even tougher in integrated circuit systems, because the transformers used in traditional methods of isolation are too bulky." (1965, p. 52).
6.2. Batch Fabrication and Integrated
In very recent years, it has been claimed that integrated circuitry is the most significant advance in computer hardware technology since the introduction of the transistor; 6.83 that it will bring important changes in the size, cost, reliability and speed of system design components,6.84 and that advanced high-speed techniques paradoxically also indicate eventual lower costs.6.85
Many potential advantages of increased usage of LSI techniques are cited in the literature. These include, for example, applications in improved central processor unit speed or capacity performance, in system control and reliability, and in content-addressable (associative) memory construction and operation.6.86 Wilkes suggests that parallelism achieved by use of these techniques may
overcome present-day deficiencies of processing systems in such applications as pattern recognition.6.87
In terms of relatively recent R & D literature, Minnick (1967) provides a review of microcellular research, with emphasis upon techniques useful for batch-fabricated circuit design; Bilous et al. (1966) discuss IBM developments of large scale integration techniques to form monolithic circuit arrays, where on only nine chips it was possible to replicate a specific System/360 computer model, and, under RADC auspices, Savitt et al. (1967) have explored both language development and advanced machine organization concepts in terms of large scale integration (LSI) fabrication techniques.6.88 That is, in general, where integrated circuits based on etched circuit board techniques had replaced discrete components, the LSI techniques of fabrication produce sheets of integrated logic components as units.6.89
To what extent do integrated fabrication techniques hold promise for future developments in very large yet inexpensive memories? Rajchman suggests that "the dominance of non-integrated memories is likely to be finally broken or at least seriously challenged by integrated memories, of which the laminated-ferrite-diode and the superconductive-thin-sheet-cryotron memories are promising examples." (Rajchman, 1965, p. 128.) And, further, that "it appears certain that energetic efforts will continue to be devoted towards integrated technologies for larger and less costly memories, as this is still the single most important hardware improvement possible in the computer art." (Rajchman, 1965, p. 128.) Other advocates. include Gross,6.90 Hudson,6.91 Van Dam and Michener,6.92 Pyke,6.93 and Conway and Spandorfer.6.94
Hobbs says of silicon-on-sapphire circuits that their fabrication is suitable for large arrays and that they are indeed "promising, but presently being pursued by only one company." (1966, p. 38.) Of active thin-film circuits, he concludes: "Potentially cheaper and easier to fabricate very large arrays. Feasibility is not proven and utilization much further away." (Hobbs, 1966, p. 38.) The same reviewer continues: "Costs are expected to range between 3 and 5 cents per circuit in large interconnected circuit arrays . . However, the ability to achieve these costs is dependent upon the use of large interconnected arrays of circuits and, hence, upon the computer industry's ability to develop logical design and machine organization techniques permitting and utilizing such arrays." (Hobbs, 1966, p. 39.)
Continuing R & D problems in terms of LSI technology include those of packaging design,6.95 error detection and correction with respect to malfunctioning components; 6.96 the proper balance to be achieved between flexibility, redundancy, and maintenance or monitoring procedures, and questions of segmentation or differentiation of functional logic types.6.97 One example of many special prob
lems is reported by Kohn as follows: "In all batch fabricated memories, the problem of unrepairable element failures is predominant . . . It is an open question how complex and expensive the additional electronic circuits will be, which will disconnect the defective elements and connect the spare ones." (Kohn, 1965, p. 132.) On the other hand, special advantages of LSI techniques for self-diagnosis and self-repair have been claimed. 6.98
6.3. Advanced Data Storage Developments
In the area of advanced hardware, the prospects for much larger, much faster, and more versatile storage systems must of course be a major R & D consideration. Current technological advances indicate the desirability of increasing use of integrated construction methods using ferrite aperture plates, thin films, laminated-diode combinations, field-effect transistors, and superconductive thin film systems, among other recent developments.6.99 For another example, possible applications of echo resonance techniques for microwave pulse delay lines that would be suitable for high-speed memories are being explored at the Lockheed Palo Alto Research Laboratory. (Kaplan and Kooi, 1966).
Advanced hardware developments for improved data storage emphasize both higher speeds of access and readout and larger capacities at higher densities of storage. There are the small capacity, ultra-highspeed, memories of the read-only, scratchpad, and associative type. These typically supplement significantly larger capacity and slower speed "main memories". Next, there are continuing prospects for high density, very large capacity stores.
There is finally the question of R & D requirements in the area where the development of "artificial" memories are designed to replicate, so far as possible, known neurophysiological phenomena. For example, Borsellino and his colleagues at the University of Genoa are studying physicalchemical simulation, such as collagen "memories", in terms of possible mechanisms of axon action, connectivity of pulses, and currents through membranes. (Stevens, 1968, p. 31).
We may thus conclude with Licklider that "insofar as memory media are concerned, current research and development present many possibilities. The most immediate prospects advanced for primary memories are thin magnetic films, coated wires, and cryogenic films. For the next echelons, there are magnetic disks and photographic films and plates. Farther distant are thermoplastics and photosensitive crystals. Still farther away- almost wholly speculative - are protein molecules and other quasi-living structures." (Licklider, 1965, pp. 63-64).
6.3.1. Main Memories
Questions of advanced tehcnological developments related to data and program information
storage and recall concern first of all the problems of "main memory"- that is, the preloaded, immediately accessible, information-recording space allocated at any one time to necessary system supervision and control, to user(s) programs and data, and to temporary work space requirements. It is to be noted that "this 'main' memory size is related to the processing rate; the faster the arithmetic and logic units, the faster and larger the memory must be to keep the machine busy, or to enable it to solve problems without waiting for data.” (Hoagland, 1965, p. 53).
Further, "this incompatibility between logic and memory speeds has led to increased parallel operation in processors and more complex instructions as an attempt to increase overall system capability." (Pyke, 1967, p. 161).
As of current technology, main memories are still usually magnetic core, with typical capacities of a million bits and cycle times of about one microsecond.6.100 One relatively recent exception is the NCR Rod Memory Computer, which is claimed to have "about the fastest main memory cycle time of any commercial computer yet delivered-800 nanoseconds." (Data Processing Mag. 7, No. 11, 12 (Nov. 1965).) This is a thin-film memory, constructed from beryllion-copper wires plated with magnetic coating.6.101
Petschauer lists the following trends which may be expected in magnetic memory developments in the near future:
"1. Trend toward simple cell structures-2 or 3 wire arrays.
"2. More automated assembly and conductor termination or batch-fabricated arrays.
"3. More fully automated plane testing. "4. More standardization.
"5. Extended use of integrated or hybrid circuits. "6. Improved methods of packaging for stack and stack interface circuits to reduce packaging and assembly costs.
"7. Reduced physical size." (Petschauer, 1967, p. 599).
With respect to current prospects for much larger, much faster main memories, Rajchman (1965) reviews possibilities for integrated construction methods using ferrite aperture plates, thin films, laminate-diode combinations, field-effect transistors, and superconductive thin film cryotrons.6.102 It is noted further that "planar magnetic film memories offer many advantages for applications as main computer storage units in the capacity range of 200K to 5M bits." (Simkins, 1967, p. 593), and that "perhaps the most significant system advantage available to users of plated magnetic cylindrical thin film memory elements is a nondestructive readout capability. For main memory use, NDRO with equal Read-Write drive currents is most advantageous. It allows the greatest possible flexibility of organization and operation. For maximum economy, many memory words (or bytes) may be ac
cessed by a single word drive line without need for more than one set of sense amplifiers and bit current drivers. The set contains only the number of amplifiers needed to process the bits of one word (or byte) in parallel." (Fedde, 1967, p. 595). Simpson (1968) discusses the thin film memory developed at Texas Instruments.6.103
Nevertheless, the known number of storage elements capable of matching ultrafast processing and control cycle times (100-nanosecond or less) are relatively few,6.104 and there are many difficulties to be encountered in currently available advanced techniques.6.105 Some specific R & D requirements indicated in the literature include materials research to lower the high voltages presently required for light-switching in optically addressed memories (Kohn, 1965),6.106 attacks on noise problems in integrated circuit techniques (Merryman, 1965),6.107 and the provision of built-in redundancy against element failures encountered in batch fabrication techniques (Kohn, 1965). In the case of cryotrons used for memory design, Rajchman (1965) notes that the "cost and relative inconvenience of the necessary cooling equipment is justified only for extremely large storage capacities" (p. 126), such as those extending beyond 10 million bits, and Van Dam and Michener (1967) concur.6.108 Considerations of "break-even" economics with respect to cryogenicelement memories such as to balance high density storage and high speed access against the "cooling" costs has been assessed at a minimum randomaccess memory requirement of 107 bits.6.109 As of 1967-68, however, practical realizations of such techniques have been largely limited to small-scale, special-purpose auxiliary and content-addressable memories, to be discussed next.
6.3.2. High-Speed, Special-Purpose, and Associative or Content-Addressable Memories
Small, high-speed, special-purpose memories have been used as adjuncts to main memories in computer design for some years.6 6.110 One major purpose is to provide increased speed of instruction access or address translation, or both. The "readonly-stores" (ROS) in particular represent relatively recent advances in "firmware," or built-in microprogramming.6.111
It is noted that "the mode of implementing ROM's spans the art, from capacitor and resistor arrays and magnetic core ropes and snakes to selectively deposited magnetic film arrays." (Nisenoff, 1966, p. 1826.) An Israeli entry involves a two-level memory system with a microprogrammed "Read Only Store" having an access time of 400 nanoseconds. (Dreyer, 1968.) A variation for instructionaccess processes is the MYRA (MYRi Aperture) ferrite disk described by Briley (1965). This, when accessed, produces pulses in sequential trains on 64 or more wires. A macro instruction is addressed to an element in the MYRA memory which then produces gating signals for the arithmetic unit and signals for fetching both operands and the next
macro instructions. Further, "Picoinstructions are stored at constant radii upon a MYRA disk, in the proper order to perform the desired task. The advantages of the MYRA element are that the picoinstructions are automatically accessed in sequence "6.112 Holographic ROM possibilities are also under consideration.6.113
In the area of associative, or content-addressable memories,6.114 advanced hardware developments to date have largely been involved in processor design and provision of small-scale auxiliary or "scratchpad" memories rather than for massive selectionretrieval and data bank management applications.6.115 "Scratchpad" memories, also referred to as "slave" memories, e.g., by Wilkes (1965),6.116 are defined by Gluck (1965) as "small uniform access memories with access and cycle times matched to the clock of the logic." They are used for such purposes as reducing instruction-access time, for microprogramming, for buffering of instructions or data that are transferable in small blocks (as in the "four-fetch" design of the B 8500),6.117 for storage of intermediate results, as table lookup devices,6 as index registers and, to a limited extent, for content addressing.6.119
Another example is the modified "interactive" cell assembly design of content-addressable memory where entries are to be retrieved by coincidence of a part of an input or query pattern with a part of stored reference patterns, including other variations on particular match operations (Gaines and Lee, 1965).6 6.120 In addition, we note developments with respect to a solenoid array 6.121 and stacks of plastic card resistor arrays, 6.122 both usable for associative memory purposes; the GAP (Goodyear Associative Processor), 6.123 the APP (Associative Parallel Processor) described by Fuller and Bird (1965),6.124 the ASP (Association-Storing Processor) machine organization,6.125 and various approaches which compromise somewhat on speed, including bitrather than word-parallel searching 6.126 or the use of circulating memories such as glass delay lines.6.127
Cryogenic approaches to the hardware realization of associative memory concepts have been under investigation since at least the mid-1950's (Slade and McMahon, 1957), while McDermid and Peterson (1961) report work on a magnetic core technique as of 1960. However, the technology for developing high-speed reactivity in these special-purpose memories has been advanced in the past few years. On the basis of experimental demonstration, at least, there have been significant advances with respect to parallel-processing, associative-addressing, internal but auxiliary techniques in the form of memories built-into some of the recently developed large computer systems.6.128
The actual incorporation of such devices, even if of somewhat limited scale, in operational computer system designs is of considerable interest, whether of 25- or 250-nanosecond performance. For example, Ammon and Neitzert report RCA experiments that "show the feasibility of a 256-word
scratchpad memory with an access time of 30 nanoseconds. . . The read/write cycle time, however, will still be limited by the amplifier recovery so that with the best transistors available it appears that 60 nanoseconds are required". (1965, p. 659). RCA developments also include a sonic film memory in which thin magnetic films and scanning strain waves are combined for serial storage of digital information.6.129
Crawford et al. (1965) have claimed that an IBM tunnel diode memory of 64 48-bit words and a read/ restore or clear/write cycle time of less than 25 nanoseconds was "the first complete memory system using any type of technology reported in this size and speed range". (p. 636).6.130 Then there is an IBM development of a read-only, deposited magnetic film memory, having high-speed read capability (i.e., 19ns access time) and promising economics because the technique is amenable to batch fabrication.6.131 (Matick et al., 1966).
Catt and associates of Motorola describe "an integrated circuit memory containing 64 words of 8 bits per word, which is compatible in respect to both speed and signal level with high-speed currentmode gates. The memory has a nondestructive read cycle of 17 nanoseconds and a write cycle of 10 nanoseconds without cycle overlap.” (Catt et al., 1966, p. 315).6.132 Anacker et al. (1966) discuss 1,000-bit film memories with 30 nanosecond access times.6.133 Kohn et al. (1967) have investigated a 140,000 bit, nondestructive read-out magnetic film memory that can be read with a 20-nanosecond read cycle time, a 30-nanosecond access time, and a 65-nanosecond write time. More recently, IBM has announced a semi-conductor memory with 40 nanosecond access.6 6.134
Memories of this type that are of somewhat larger capacity but somewhat less speed (in the 100-500 nanosecond range) are exemplified by such commercially-announced developments as those of Electronic Memories,6.135 Computer Control Company, 6.136 and IBM.6.137 Thus, Werner et al. (1967) describe a 110-nanosecond ferrite core memory with a word capacity of 8,192 words,6.138 while Pugh et al. (1967) report other IBM developments involving a 120-nanosecond film memory of 600,000-bit capacity. McCallister and Chong (1966) describe an experimental plated wire memory system of 150,000-bit capacity with a 500-nanosecond cycle time and a 300nanosecond access time, developed at UNIVAC.6. Another UNIVAC development involves planar thin films.6.140 A 16,384-word, 52-bit, planar film memory with half-microsecond or less, (350 nanosecond) cycle time, under development at Burroughs laboratories for some years, has been described by Bittman (1964).6.141 Other recent developments have been discussed by Seitzer (1967) 6.142 and Raffel et al. (1968),6.143 among others.
For million-bit and higher capacities, recent IBM investigations have been directed toward the use of "chain magnetic film storage elements" 6.144 in both DRO and NDRO storage systems with 500
nanosecond cycle times.6.145 It is noted, however, that "a considerable amount of development work is still required to establish the handling, assembly, and packaging techniques." (Abbas et al., 1967, p. 311).
A plated wire random access memory is under development by UNIVAC for the Rome Air Development Center. "The basic memory module consists of 107 bits; the mechanical package can hold 10 modules. The potential speed is a 1-to-2 microsecond word rate. . . . Ease of fabrication has been emphasized in the memory stack design. These factors, together with the low plated wire element cost, make an inexpensive mass plated wire store a distinct possibility." (Chong et al., 1967, p. 363).6.146 RADC's interests in associative processing are also reflected in contracts with Goodyear Aerospace Corp., Akron, Ohio, for investigation and experi mental fabrication of associative memories and processors. (See, for example, Gall, 1966).
6.3.3. High-Density Data Recording and Storage
Another important field of investigation with respect to advanced data recording, processing, and storage techniques is that of further development of high-density data recording media and methods and bulk storage techniques, including block-oriented random access memories.6.147 Magnetic techniques - cores, tapes, and cards - continue to be pushed toward multimillion bit capacities.6.148 A single-wall domain magnetic memory system has recently been patented by Bell Telephone Laboratories.6.149 In terms of R & D requirements for these techniques, further development of magnetic heads, recording media, and means for track location has been indicated,6.150 as is also the case for electron or laser beam recording techniques.6.151 Videotape developments are also to be noted. 6.152
In addition to the examples of laser, holographic, and photochromic technologies applied to high density data recording previously given, we may note some of the other advanced techniques that are being developed for large-capacity, compact storage. These developments include the materials and media as well as techniques for recording with light, heat, electrons, and laser beams. In particular, "a tremendous amount of research work is being undertaken in the area of photosensitive materials. Part of this has been sparked by the acute shortage of silver for conventional films and papers. In October, more than 800 people attend a symposium in Washington, D.C., on Unconventional Photographic Systems. Progress was described in a number of areas, including deformable films, electrophotography, photochromic systems, unconventional silver systems, and photopolymers.' (Hartsuch, 1968, p. 56).
Examples include the General Electric Photocharge,6.153 the IBM Photo-Digital system,6.154 the UNICON mass memory, 6.155 a system announced