Abstract: The Shared Control Parallel Architecture Model.

SIMD machines are considered special purpose architectures chiefly because of their inability to support control parallelism. This restriction exists because there is a single control unit that is shared at the thread level; concurrent control threads must time-share the control unit (they are sequentially executed). We present an alternative model for building centralized control architectures that allows better support for control parallelism. This model, called {\em shared control}, shares the control unit(s) at the instruction level. More precisely, in each cycle the control signals for all the supported instructions are broadcast to the PEs. In turn, each PE receives its control by synchronizing with the control unit responsible for its local instruction. The shared control model is fundamentally different from the SIMD model. There are a number of architectural issues that have to be resolved in order for this model to be useful. This paper identifies some of these issues and discusses their respective tradeoff spaces. An integrated shared-control/SIMD architecture design (SharC) is presented and used to demonstrate the relative performance relative to a SIMD architecture.