James B. Morris

Demand paging through utilization of working sets onr the MANIAC II

A hardware implementatio~ on the Maniac II computer of the s.orking set model fur demand paging, as intr~duced by Denning, is discussed. Characteristics of the Maniac II are given, along wi~th a description of the basic demand paging scheme and the associative memory which has hee~ added to the Maniac 1I hardware. Finally, a description of the hardware design for impiementati(m of ~he working s~t model is discussed and a specification of the actions taken under ~arious conditions which may ar i~ during the operation of the full working set mode|, demand ~aging system is given.

The unified data structure capability in Madcap VI

The data structures which form an integral part of the Madcap VI programming language are described. The initialization (declarationand constructor) expressions and selector expressions of these structures are defined and their implementation using “codewords” is discussed. Structures, since they can contain references to other structures (including themselves), have the form of directed trees (graphs). Variables of primitive data type (real, complex, etc.) are naturally considered as degenerate graphs, merely single nodes. The possibility for both multiword and fractional-word representation of structures is evident, but the language itself is implementation-independent. Thus a “field” is simply a substructure. The Madcap VI data structures are compared to data structure concepts in PL/I.

Abstract data types in the Model programming language

The concept of an abstract data type is available in the Model programming language as a proposed improvement to current ideas of programming methodology. In structured programming the principal technique is refinement of procedures. In Model, the analogue is refinement of data types. An abstract data type consists of a data structure and an associated set of operations. The characteristics and suggested uses for this mechanism are discussed. Also presented are several examples culminating in a parallel version of the Fast Fourier Transform.

Ada for the Intel 432 Microcomputer

Ada represents a new era in language standards and software portability. It is the primary language of Intels new micromainframe, which directly supports many of its features.

A result on the relationship between simple precedence languages and reducing transition languages

Two of the more recently published systems for the efficient parsing of subclasses of deterministic, context-free languages are the <underline>backwards-deterministic</underline>, (or <underline>unambiguous</underline>, as they were originally called) <underline>simple precedence languages</underline> due to Wirth and Weber, and the <underline>reducing transition languages</underline> due to Eickel, Paul, Bauer, and Samelson. The main result demonstrated in this paper is that the backwards-deterministic, simple precedence languages are a <underline>proper subclass</underline> of the reducing transition languages. The reducing transition languages are certainly a subclass of the deterministic, context-free (LR(1)) languages but it is not known if this inclusion is proper. The major complaint against the reducing transition languages is the large amount of memory required when this technique is utilized with large grammars, such as the ALGOL 60 grammar. With memory costs and physical memory sizes decreasing at a rapid rate, it is very possible that this disadvantage will not exist in the not-too-distant future. When this becomes true, the advantage of reducing transition languages, i.e., the relatively small amount of time required for their parsing, may result in their significance being substantially increased. Thus it is of some import that we study their relationship to other languages. The main result is based on two theorems: (1) if G is a backwards-deterministic simple precedence grammar, then G is a reducing transition grammar; and (2) the language L<subscrpt>1</subscrpt> &equil; {a0<supscrpt>n</supscrpt>1<supscrpt>n</supscrpt>2<supscrpt>m</supscrpt>¦m,n ≥ 1} &ugr; {b0<supscrpt>n</supscrpt>1<supscrpt>m</supscrpt>2<supscrpt>n</supscrpt>¦m,n ≥ 1} is a reducing transition language but is not a backwards-deterministic simple precedence language.

Programming by semantic refinement

It is becoming increasingly evident that human programmers are not capable of efficiently producing reliable programs if they must be concerned initially with every detail of the final program. The approach described here is one of “semantic levels of programming”, which involves a graduated approach to the production of programs. A common but fallacious belief of some software implementors today is that the efficient execution of software systems should be a major concern in the initial system version. In fact, the primary concern in the initial version should be the reliable operation of the system, which is closely connected with the existence of a sound, overall system design. Assuming that we recognize that there is some reasonable time from the initiation of a software system implementation project to the availability of an initial version, the philosophy of semantic refinement is based on the belief that: “If a major concern in the implementation of the initial version of a software system is efficiency, then the initial version will be unreliable.” Many systems which are initially unreliable have a way of remaining unreliable for a discouragingly long period of time.