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Protection and the control of information sharing in multics
The design of mechanisms to control the sharing of information in the Multics system is described. Five design principles help provide insight into the tradeoffs among different possible designs. The key mechanisms described include access control lists, hierarchical control of access specifications, identification and authentication of users, and primary memory protection. The paper ends with a discussion of several known weaknesses in the current protection mechanism design.
HYDRA: the kernel of a multiprocessor operating system
This paper describes the design philosophy of HYDRA—the kernel of an operating system for C.mmp, the Carnegie-Mellon Multi-Mini-Processor. This philosophy is realized through the introduction of a generalized notion of “resource,” both physical and virtual, called an “object.” Mechanisms are presented for dealing with objects, including the creation of new types, specification of new operations applicable to a given type, sharing, and protection of any reference to a given object against improper application of any of the operations defined with respect to that type of object. The mechanisms provide a coherent basis for extension of the system in two directions: the introduction of new facilities, and the creation of highly secure systems.
On Lion’s counter example for Gotlieb’s method for the construction of school timetables
The timetable problem is an essentially discrete problem. Although the discrete problem may have no feasible solution, there may exist a solution to the equivalent continuous problem. An example, is given, for which the nondiscrete solution can be interpreted as a set of timetables, differing from week to week, which together satisfy the long-term requirements of the timetable problem.
On the construction of a representative synthetic workload
A general method of constructing a drive workload representative of a real workload is described. The real workload is characterized by its demands on the various system resources. These characteristics of the real workload are obtained from the system accounting data. The characteristics of the drive workload are determined by matching the joint probability density of the real workload with that of the drive workload. The drive workload is realized by using a synthetic program in which the characteristics can be varied by varying the appropriate parameters. Calibration experiments are conducted to determine expressions relating the synthetic program parameters with the workload characteristics. The general method is applied to the case of two variables, cpu seconds and number of I/O activities; and a synthetic workload with 88 jobs is constructed to represent a month's workload consisting of about 6000 jobs.
Advanced cryptographic techniques for computer
Cryptographic techniques which can be used to maintain the confidentiality of information processed by computers are dealt with. Special emphasis is paid to the unique characteristics of computer files that make many cryptographic methods of little use. Relative security, costs, and preferred methods are included in this paper.
Numerical analysis in a Ph.D. computer science program
Numerical Analysis is the study of methods and procedures used to obtain“approximate solutions” to mathematical problems. Much of the emphasis is on scientific calculation. The difficulties of education in such a broad area center around the question of background and emphasis. The Numerical Analysis program in the Computer Science Department should emphasize an awareness of the problems of computer implementation and experimental procedures. Nevertheless, there is a need for a solid background in applied mathematics.
Performance monitoring in a time-sharing system
A software measurement facility which is part of a general purpose time-sharing system is described. The Data Collection Facility (DCF) has been implemented in the Michigan Terminal System (MTS) for the System/360 model 67. It exists for the purpose of monitoring operating system and user program behavior and performance. The overall structure of MTS is outlined in order to explain the implementation of the DCF. Events in the system are identified and recorded from within the supervisor, and dumped to magnetic tape by an auxiliary program for off-line processing. Events in user programs which are unrelated to system actions are recorded with a supervisor call. The time of occurrence of each event is accurately recorded, and data items are further identified by job and type. The overhead associated with data collection and its interference with normal jobs is carefully analyzed, and both are shown to be minimal. Several examples are given of information obtained with the facility and of applications in which it has been useful. Some general guidelines are offered for the construction of future monitoring programs.
The IITRAN programming language
The IITRAN language, developed to be used by students, and its important features are described. IITRAN is a procedure-oriented language with a one-level block structure and a variety of data types. Several novel and powerful features are included. A discussion of design principles to be followed in a student language is given.
A modular computer sharing systems
An alternative approach to the design and organization of a general purpose interactive multiterminal computing system is presented. The system organization described is a conceptually simple arrangement of a bank of interchangeable computers, each of which is a memory/proputor pair, that are assigned to process terminal jobs as they arrive. One of the computers serves as the master or control computer and supervises the collection and distribution of messages from and to the remote terminals. In the simplest form there is a disk drive for each connected terminal. A crosspoint switching network allows any such disk drive to be connected to any computer in the bank, under control of the control computer. Thus, while each active terminal user “occupies” a dedicated disk drive, he may share the computer with many other terminal users in a simple manner. The ratio of users to computers is dependent on both the size and power of the machines used and the computation requirements of the particular mix of users.
This system organization is inherently a simpler and therefore more reliable approach to time-sharing computers and has the potential of a highly available system at relatively low cost. Economic configurations are possible for a range of systems sizes that span at least one order of magnitude. Finally, problem programs developed by remote terminal users can be run on a dedicated batch system if compatible computers are used.
Loader standardization for overlay programs
The overlay capability is described for four of the third generation computer systems: CDC-6000, GE-635, IBM-360, and UNIVAC-1108. A critique of the first three sytems is based on actual experience with a large overlaid trajectory simulation program; a short history and description of this program is presented. A standardization of minimum capabilities for loaders is recommended so that programs which must operate under more than one computer system may be easily converted and maintained. A proposal that overlay software incorporates a memory occupation specification concept instead of the conventional tree structure is delineated. This concept provides more efficient and cost-effective utilization of the memory as well as increasd flexibility in program structure.
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