Bruce W. Arden

Program and Addressing Structure in a Time-Sharing Environment

The problem studied is the effect of a time-sharing environment on the structure of programs and on the addressing strategies which may be employed in the hardware. An account is given of some very recent developments toward reduction in the system overhead needed to facilitate time-sharing. One hardware-software scheme designed to implement this reduction is described in some detail.

An Algorithm for Translating Boolean Expressions

Abstract. This paper describes an algorithm for scanning Boolean expressions. Such an algori thm takes a complex, relational expression and transforms it into an opt imal set of computing steps. The result is opt imal in the sense tha t no redundant evaluat ions are made. The par t icular algori thm described is advantageous in that , as a var iant of a well-known arithmetic scan, it fits into a general scheme for the translation of statements to machine language. Consistent with this arithmetic expression scan, which is included as a starting point for the development, this Boolean scan does not require the re-ordering of subexpressions.

On GAT and the construction of translators

The Generalized Algebraic Translator (GAT) was written at the University of Michigan Statistical and Computing Laboratory for a 650 with index registers, floating point arithmetic, and special characters. Some of the main features of the Translator are: (a) Single pass. Optimized five/card machine instructions are produced directly from the original statements. Floating point and indexing instructions are generated. (b) Variables. Variable names are subscripted letters, as in IT, although a larger set of letters is allowed. Variables are either fixed point integers or floating point, and subscription is reeursive. (c) Constants. Constants may be written in a st~aternent and may be either floating, :fixed, or alphabetic. (d) Subroutines. Subroutines are called by using arbit rary alphanumeric names. All subroutines are reloeatable. (e) Conventional operational hierarchy. Unparenthesized expressions are interpreted according to the commonly accepted algebraic conventions. (f) Input-output. Ei ther mlmerie or alphanumeric information, identified by its appropriate symbolic labels, may be read or produced as output during execution of the object program. (g) Mixed arithmetic. Variables or constants of fixed point integer and floating point form may be included in the same expression. (h) Iteration statements. Iteration variables may be fixed or floating and it is possible to make an arbitrary transformation of the designated variable. Also the initial and final values may be arbi t rary expressions. (i) Matrix manipulation. The base variable and row length may be specified in a dimension statement as integer variables. Thus, during execution, regions may be essentially reassigned and subnmtrices may be considered as independent matrices. The translation techniques employed in GAT may be considered as a special ease of what seems to be a good, generM translation scheme.

Measurement and performance of a multiprogramming system

This paper presents a brief description of a general multiprogramming (and time-sharing) system in operation at the University of Michigan. A number of time and space distributions obtained from a typical month of operation are presented. The performance is summarized by a load diagram. Efficiency as a comparison with ideal performance is discussed and a model suitable for idealization is proposed.

An algorithm for equivalence declarations

Many algebraic translators provide the programmer with a limited ability to allocate storage. Of course one of the most desirable features of these translators is the extent to which they remove the burden of storage allocation from the programmer. Nevertheless, there are situations in which one wishes to make certain vectors and arrays contiguous, coincident, or overlapping. This is made possible in FORTRAN by the use of COMMON and EQUIVALENCE statements, in MAD by the use of PROGRAM COMMON, ERASABLE, and EQUIVALENCE statements, etc.

A multi-microprocessor computer system architecture

The development of microprocessors has suggested the design of distributed processing and multiprocessing computer architectures. A computer system design incorporating these ideas is proposed, along with its impact on memory management and process control aspects of the systems operating system. The key design feature is to identify system processes with microprocessors and interconnect them in a hierarchy constructed to minimize intercommunication requirements.

The MAD definition facility

One of the first definition facilities for higher level languages is described. Users of the language can define new operators and/or data types into the MAD language, so that their use appears as if they were predefined. Information is given on how one writes definitions, as well as on much of the motivation behind the form in which definitions are written. Some conclusions are drawn about future definitional facilities.

The role of programming in a Ph.D. computer science program

In this general paper the role of programming in advanced graduate training is discussed. Subject matter related to programming as well as programming per se is considered. The importance and application of formalism are considered and also the need for good empirical experimentation. A brief outline for a sequence of courses is included, and subject headings that have been obtained from an extensive bibliography are given. A bibliography of programming references is included.

On introducing digital computing

Broadly stated, the goals of instruction are to impart factual knowledge or useful skills or both which, in turn, will aid the recipient in meeting and understanding new situations. Such a truism certainly applies to instruction in the emerging field of computing, but the relative newness and rapid growth of the field create problems in designing courses based on this dicta. One problem, which is shared by any course designer whose subject matter is based in large measure on a rapidly developing technology, is to select for presentation those facts, from the brief history and current practice, that will have a lasting relevance. A similar selection problem exists in thc area of skills. The feeling exists that the skills imparted should transcend the specific details of current practice but, if this view is adopted, the problem becomes one of defining such skills and discovering how they differ, if at all, from the goals of more established courses in mathematics, logic, etc. One answer to these selection problems is to avoid them; that is, teach a variety of topics of current interest and let the selection be done, in time, by the student who will hopefully retain what continues to be useful. This approach may well be the best in a developmental era but, perhaps, some insight can be gained by briefly considering the subject matter and skills relevant to digital computer programming.