On-Line Computing With a Hierarchy of Processors

Time shared computer systems have been based upon the two techniques of multiprogramming and swapping. Multiprogramming is based on restricting each program to a portion of the total computer memory. Swapping requires considerable overhead time for loading and unloading programs. To alleviate the size restriction due to multiprogramming, segmentation is employed, resulting in fact in vastly increased swapping. A new system architecture is proposed for time shared computing that alleviates the high overhead or program size restriction. It utilizes a hierarchy of processors, where each processor is assigned tasks on the basis of four factors: interactive requirements, frequency of use, execution time, and program length. In order to study the hierarchical approach to system architecture, the Moore School Problem Solving Facility (MSPSF) was built and used. The study of the manner of operation and the reactions of the users clarified and defined the Hierarchy of Processors system architecture. The Moore School Problem Solving Facility was implemented on second generation equipment, the IBM 7040, and therefore it is not possible to adequately compare the efficiency with third generation computers operating in a swapping mode. The conclusions of this dissertation center around the methodology of designing such a system, including the specification of facilities for each level of the hierarchy. Six major conclusions are given: (1) Three processors in the hierarchy have been necessary, but it is conceivable that more may be employed in other future situations. (2) Each of the processors in the hierarchy should be general purpose. (3) Program compatibility between the processors is necessary. (4) The assigning of tasks to the processors within the system should be optionally user directed or automatic. Similarly, if a task exceeds the resources of the processor to which it has been assigned, redirection should be possible either automatically or by the user. (5) A macro language is necessary between every pair of processors for effective communication. Such a language processor, IXSYS, has been constructed and its use is described in detail in the dissertation, demonstrating the need and utility. (6) In addition to the three hierarchical processors, a separate processor may be advantageously used for storage, retrieval and management of information in files. Such a processor should be directly accessible from each of the other processors

An Interactive Graph Theory System

The medium of computer graphics provides a capability for dealing with pictures in man-machine communication. Graph Theory is used to model relationships which are represented by pictures and is therefore an appropriate discipline for the application of an interactive computer graphics system. Previous efforts to solve Graph Theoretic problems by computer have usually involved specialized programs written in a symbolic assembly language or algebraic compiler language. In recent years, graphics equipment with processing power has been commercially available for use as a remote terminal to a large central computer. Although these terminals typically include a small general purpose computer, the potential of using one as programmable subsystem has received little attention. These motivations have led to the design and implementation of an interactive graphics system for solving Graph Theoretic problems. The system operates on an IBM 7040 with a DEC-338 graphics terminal connected by voice-grade telephone line. To provide effective response times, computing power is appropriately divided between the two machines. The remote computer graphics terminal is controlled by a special-purpose executive program. This executive includes an interpreter of a command language oriented towards the control of existence and display of graphs. Several interactive functions such as graph drawing and editing are available to a user through light button and pushbutton selection. These functions which are local to the terminal are programmed in a mixture of the terminal computer\u27s machine language and the interpreted command language. For more significant computational requirements the central computer is used, but response time for interactive operation is then diminished. In order to overcome the speed of the telephone link, the central computer may call upon a program at the terminal as a subroutine. Based on the mathematical terminology used to define graphs, a high level language was developed for the specification of interactive algorithms. A growing library of these algorithms provides routines to aid in the construction and recognition of various types of graphs. Other routines are used for computing certain properties of graphs. Graphs may be transformed by some routines with respect to both connectivity and layout. Any number of graphs my be saved and later restored. A programmer using the terminal as an alphanumeric console may call upon the programming features of the system to develop new interactive algorithms and add them to the library. Programs may also be created for the display terminal, using the central computer for assembly. Examples of system use which are presented include finding a shortest path between any pair of vertices in a weighted directed graph, determining the maximally complete subgraphs of an arbitrary graph, interpreting a graph as a Mealy model of a finite state machine, and laying out a tree for aesthetic presentation