摘要:

The storage of information in present day computer systems is shared between high‐speed, high‐cost memories and low‐speed, low‐cost mechanical storage devices. With the advent of cheap bulk memory technology one can envision a storage hierarchy with three levels of storage: buffer, memory, and a mechanical backing store. The individual cost and performance characteristics of the three technologies involved affect the overall computer system cost‐performance. In fact, it is the judicious selection of technologies and system configurations which leads to a well designed storage system. This paper first describes the automatic management of information in a three level storage system where the objective is to keep current information in the fastest device and the rest of the information in the slower devices. Then the evaluation of the storage systems is described for a multiprogramming environment where total system dollars per instruction executed is the criterion for system cost‐performance. Finally, two examples are given, one to illustrate how to select the best technology for use at any level of a storage hierarchy and another to determine the cost‐performance goals which must be met by a new technology in order to be competitive with existing products in the storage system.

ISSN:0094-243X    

DOI:10.1063/1.3699391

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

A definition is presented for high‐speed memories, and the spectrum of uses ranging from extended main memories to buffers is examined. An analysis is made of factors influencing total cost and performance of both magnetic and semiconductor memories in terms of drive requirements, array costs, failure rate, access time, propagation delay, connections, packaging, power consumption, modularity, debugging ease, and integrated circuit compatibility. Fundamental economic and performance factors such as cell density, batch size, cell complexity and power dissipation also are examined to highlight future potential development in each area. In addition, business factors such as second source availability, industry commitment, general technical under‐, standing and training requirements are considered. Finally, a projection is made indicating a growth in both magnetic and semiconductor memories for the next several years with the largest percentage growth in semiconductor memories.

ISSN:0094-243X    

DOI:10.1063/1.3699392

出版商:AIP    

年代:1972

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.3699393

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Magnetic recording on flexible tape or rigid disks has become the dominant form of low‐cost storage for computer systems because it utilizes an inexpensive, removable, nonvolatile, read‐write media capable of supporting very high density and high‐speed operation. While solid state storage technologies may replace magnetic recording for small units or for very high performance, only beam addressable storage (BAS) has most if not all of the features required to be considered as a general alternative to magnetic recording in information processing systems. A number of difficult engineering and materials problems are identified, however, which must be solved before this alternative can be realized.

ISSN:0094-243X    

DOI:10.1063/1.3699394

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

The evolution of magnetic “bubble” technology has continued at a rapid pace. Many garnet compositions, prepared as epitaxial films, are now available for both materials and device characterization. Films of the nominal composition Er2Eu1Ga.7Fe4.3012, grown by LEE with growth induced anisotropy, have been most extensively studied. Although films with defect counts less than 5 defects/cm2are readily produced, this particular garnet is hampered by the rather modest mobility of 80 cm/sec/0e and 100 kbits/sec device data rates. Although most garnets easily provide storage densities of 106bits/in2, the higher device data rates achievable with increased mobility have prompted a widespread materials search. However, improvements in bubble propagation circuits can also increase the device data rate. Improved high speed performance has been achieved with a “chevron” bubble circuit which consists of columns of permalloy ∧'s arranged as “(see PDF for diagram)”. Domains will be driven to the right by the fields of moving lines of magnetic poles generated by an in‐plane field rotated clockwise. Within the range of device operation either bubbles or island strip domains propagate. The number of ∧'s in a column can be adjusted to suit individual circuit requirements. For example, a two element 20 &mgr;m period chevron circuit has operated at 300 kHz with an epitaxial garnet film Er1.99Gd1.01Ga.22Fe4.78012 with a mobility 89 cm/sec/0e. Simultaneous propagation of as many as three domains with movement lateral to the direction of propagation in a 13 element circuit has made possible the design of a full adder. Details of a chevron bubble mass memory will be described.

ISSN:0094-243X    

DOI:10.1063/1.3699395

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

The current methods of preparation of high quality magnetic garnet epitaxial films for bubble domain devices will be presented. This will include the Czochralski growth of defect free gallium garnet substrate crystals through optimizing the conditions of growth, especially the crystal rotation rate, the pulling rate and the oxygen over pressure. Methods of processing substrate wafers which have low surface defect densities will be described. The current status of the two methods of film deposition, liquid phase epitaxy and chemical vapor deposition, will be discussed with emphasis on the control of magnetic parameters such as moment, anisotropy, coercivity and domain mobility by adjustment of growth conditions and film composition.

ISSN:0094-243X    

DOI:10.1063/1.3699396

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Some of the pertinent features of the growth‐induced noncubic anisotropy in flux‐grown garnets, developed for bubble devices, are reviewed. Earlier theories based on the concept of a growth‐induced ion pairing or a growth‐induced nonrandom distribution of ions in the rare earth sublattice are reinterpreted in terms of a two parameter phenomenological model. Torque measurements on several bulk garnet systems are then compared with this model, and the theory is then extended with reasonable success to epitaxial garnet films. The two phenomenological parameters in this model are defined in terms of site preferences dependent on the relative sizes of the rare earth ions, and in terms of magnetic interactions involving the anisotropic exchange fields acting on these ions. We show how this theory is able to account for the recent ESR experiments that have verified the hypothesis of a growth‐induced facet dependent site selectivity in the rare earth sublattice. We conclude by indicating how a study of this growth‐induced anisotropy can be used as a powerful new technique for investigating the anisotropic exchange fields acting on rare earth ions in garnets.

ISSN:0094-243X    

DOI:10.1063/1.3699397

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Various theories have been given for the non‐cubic anisotropy arising from preferential site ordering of rare earth ions. It is stressed that all are symmetry theories, making no essential reference to mechanisms. Gyorgy et al1have given a theory based on macroscopic crystal symmetry, and a more detailed version based on site symmetry. Rosencwaig et al2and H. Callen3have focussed on the symmetry of each successive shell of neighbors, to isolate the dominant interactions responsible for the anisotropy. Possible mechanisms are reviewed and their inferences for temperature dependence is described. Concentration dependence of the effect is also reviewed.4Aline Akselrad5has recently observed growth‐induced non‐cubic anisotropy in garnets with a single rare earth, precluding preferential ordering in dodecahedral sites, and in garnets with purely diamagnetic dodecahedral ions, precluding anisotropic exchange interactions. In these cases Akselrad and Callen5have shown that the effect may be a single‐ion anisotropy of tetrahedral iron ions, whose symmetry is lowered by preferential site ordering among the neighboring tetrahedral sites. Dodecahedral ordering has the same effect on tetrahedral iron, and it almost certainly contributes a somewhat smaller but significant anisotropy in mixed rare earth garnets. Again these alternate models of growth‐induced anisotropy are discussed in detail, stressing physical mechanisms.

ISSN:0094-243X    

DOI:10.1063/1.3699398

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Motion of magnetic domain walls in magnetic bubble domain materials is discussed in this paper. A steady‐state solution for wall velocity in a magnetic material with orthorhombic anisotropy is used to obtain the conventional expression for the domain wall mobility. After reviewing the experimental situation, it is concluded that the mobility depends in a predictable way on wall width but that its detailed behavior otherwise is not well understood. Limiting wall velocities, nonlinear velocity‐field behavior, and wall inertial effects are considered, and important consequences of the orthorhombic anisotropy appear here; supporting experimental results for these effects are reviewed. Wall motion damping due to anisotropic energy levels in several of the magnetic rare earths is shown to be a limiting factor in obtaining high mobility materials. Other factors which have been shown to be significant, such as surface smoothness, thermal annealing, and irradiation with X‐rays, are also discussed. Finally, expressions are developed which relate the data rate for bubble devices to magnetic material parameters. An upper limit of about 10 MHz is predicted for a typical epitaxial garnet film having 3 micron diameter bubbles, this limit depending inversely on the square of the bubble diameter.

ISSN:0094-243X    

DOI:10.1063/1.3699399

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Magnetic bubble devices require materials with a single easy‐axis of magnetization stably oriented normal to the device plane. We show that epitaxial films of cubic materials possessing growth‐ or stress‐induced anisotropies satisfy this condition in general only for {100}, {111}, and {110} orientations. Further conditions which must be fulfilled are −A′ > |Kl| + 2&pgr;M2for {100} films, −B′ > 4&pgr;M2for {111}, for {111}, and −(A′ +12B′) > |Kl|, + 4&pgr;M2and − B′ > 4&pgr;M2for {110}, where A′ = A + 30o&lgr;100/2 and B′ = B + 30o&lgr;111. Here &sgr;ois the in‐plane stress and A and B are the phenomonological constants of Gyorgyet al. describing the growth‐induced anisotropy. In bulk garnet crystals, material from {211} facets with its easy axis along <110> in the growth plane would be suitable for bubble applications. {211} facet material with its easy axis at an arbitrary angle in the {110} plane containing the facet normal is less desirable, since the angle is expected to be temperature sensitive. The induced easy axes of {110} facet material are symmetry directions, and no such difficulties are expected.

ISSN:0094-243X    

DOI:10.1063/1.3699400

出版商:AIP    

年代:1972

数据来源: AIP