Media-access delays in HUBNET, a high-performance local area network, are examined. An experimental technique for loading such a network with data up to 97.5% of its nominal bit rate is described. The results of a series of measurements of the packet-access delay in a network operating at loads up to 87.5% of capacity are presented. A modeling technique for this process is developed, and the results of calculations based on that model are compared to the experimental results. Extremely good agreement is obtained. The model is then used to examine the network behavior comprehensively over an extensive range of parameters.>

A processor for the Smalltalk-80↑ programming language is described. This machine is implemented using a standard bit slice ALU and sequencer, TTL MSI, and NMOS LSI RAMS. It executes an instruction set similar to the Smalltalk-80 virtual machine instruction set. The data paths of the machine are optimized for rapid Smalltalk-80 execution by the inclusion of a context cache, tag checking, and a hardware method cache. Each context is only partly initialized when created, and has no memory allocated for it until a possibly non-LIFO reference to it is created. The machine is microprogrammed, and uses a simple next micro-address prediction strategy to obtain most of the performance of pipelining without the attendant complexity. The machine can execute simple instructions at over 7M bytecodes per second and has a predicted average throughput of 1.9M bytecodes per second.