Our view is that people (that is, programmers and general computer users) tend to work together in small groups, where information and resources are shared freely within a group. Most interactions occur within the group (called a cluster)-sending messages, exchanging data, sharing a printer. Communication outside the cluster-sending mail to someone in another group or using a large number cruncher-is comparalively rare. Under this hypothesis, it is advantageous to optimize and simplify interactions within the group. This paper describes our attempt to design a cluster network based on a nonblocking crosspoint switch, which we call ALAN (a local area net). ALAN clusters are star-connected-with intelligent workstation nodes (PC's) at the points of the star, and the ALAN switch at the center.

Execution architectures include Directly Executed Languages, or DEL's, which are tailored to particular combinations of software and hardware technologies. In this paper, we review the general notion of DEL's, and show how they compare to traditional instruction set architectures. We focus on general techniques for synthesizing DEL's rather than performance questions per se, however. There are four aspects to this design problem: Naming: relating identifiers to objects. Formatting: associating objects to arguments/results. Control: specifying the order of interpretation. Function: operating on objects identified by the naming and format mechanisms, in the order specified by the control mechanism.

Several methods of evaluating user programs are analyzed with respect to space and time requirements. The concept of an "ideal" directly executed language is introduced and it is argued that the "ideal" directly executed language for a contemporary computing system will not be either its source language or the language accepted by its base machine.