Autonet is a self-configuring local area network composed of switches interconnected by 100 Mb/s, full-duplex, point-to-point links. The switches contain 12 ports that are internally connected by a full crossbar. Switches use cut-through to achieve a packet forwarding latency as low as 2 ms/switch. Any switch port can be cabled to any other switch port or to a host network controller. A processor in each switch monitors the network's physical configuration. A distributed algorithm running on the switch processor computes the routes packets are to follow and fills in the packet forwarding table in each switch. With Autonet, distinct paths through the set of network links can carry packets in parallel, allowing many pairs of hosts to communicate simultaneously at full link bandwidth. A 30-switch network with more than 100 hosts has been the service network for Digital's Systems Research Center since February 1990. >

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Autonet: a high-speed, self-configuring local area network using point-to-point links

Firefly is a shared-memory multiprocessor workstation that contains from one to seven MicroVAX 78032 processors, each with a floating point unit and a sixteen kilobyte cache. The caches are coherent, so that all processors see a consistent view of main memory. A system may contain from four to sixteen megabytes of storage. Input-output is done via a standard DEC QBus. Input-output devices are an Ethernet controller, fixed disks, and a monochrome 1024 x 768 display with keyboard and mouse. Optional hardware includes a high resolution color display and a controller for high capacity disks. Figure 1 is a system block diagram.The Firefly runs a software system that emulates the Ultrix system call interface. It also supports medium- and coarse-grained multiprocessing through multiple threads of control in a single address space. Communications are implemented uniformly through the use of remote procedure calls.This paper describes the goals, architecture, implementation and performance analysis of the Firefly. It then presents some measurements of hardware performance, and discusses the degree to which SRC has been successful in producing software to take advantage of multiprocessing.

Firefly: a multiprocessor workstation

Statically-typed programming languages allow earlier error checking, better enforcement of disciplined programming styles, and generation of more efficient object code than languages where all type-consistency checks are performed at runtime. However, even in statically-type languages, there is often the need to deal with data whose type cannot be known at compile time. To handle such situations safely, we propose to add a type Dynamic whose values are pairs of a value v and a type tag T where v has the type denoted by T. Instances of Dynamic are built with an explicit tagging construct and inspected with a type-safe typecase construct.This paper is an exploration of the syntax, operational semantics, and denotational semantics of a simple language with the type Dynamic. We give examples of how dynamically-typed values might be used in programming. Then we discuss an operational semantics for our language and obtain a soundness theorem. We present two formulations of the denotational semantics of this language and relate them to the operational semantics. Finally, we consider the implications of polymorphism and some implementation issues.

Dynamic typing in a statically-typed language

Statically typed programming languages allow earlier error checking, better enforcement of diciplined programming styles, and the generation of more efficient object code than languages where all type consistency checks are performed at run time. However, even in statically typed languages, there is often the need to deal with datawhose type cannot be determined at compile time. To handle such situations safely, we propose to add a type Dynamic whose values are pairs of a value v and a type tag T where v has the type denoted by T. Instances of Dynamic are built with an explicit tagging construct and inspected with a type safe typecase construct.This paper explores the syntax, operational semantics, and denotational semantics of a simple language that includes the type Dynamic. We give examples of how dynamically typed values can be used in programming. Then we discuss an operational semantics for our language and obtain a soundness theorem. We present two formulations of the denotational semantics of this language and relate them to the operational semantics. Finally, we consider the implications of polymorphism and some implementation issues.

Dynamic typing in a statically typed language

This paper provides an introduction to writing concurrent programs with “threads”. A threads facility allows you to write programs with multiple simultaneous points of execution, synchronizing through shared memory. The paper describes the basic thread and synchronization primitives, then for each primitive provides a tutorial on how to use it. The tutorial sections provide advice on the best ways to use the primitives, give warnings about what can go wrong and offer hints about how to avoid these pitfalls. The paper is aimed at experienced programmers who want to acquire practical expertise in writing concurrent programs.

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An Introduction to Programming with Threads

Designed to build both system and application software for large systems, Modula-2+ supports exception handling, automatic storage management, and concurrency for multiprocessors without compromising the integrity of Modula-2.

P. Rovner

Papers

Extending Modula-2 to Build Large, Integrated Systems