PLMGMCommunication NetworkPLM0N-1Global MemoryProcessors,
Local Memories

Fig. 1. P-RISC abstract machine model

It is important to emphasize that this is an abstract machine model only. It may be implemented on a multicomputer, with each node's physical local memory partitioned into the (logical) Local Memory and a part of the (logical) Global Memory.

Figure 2 shows the runtime state for P-RISC graphs. Each processor runs a number of micro-threads concurrently (logically; in practice, the processor is multiplexed amongst them). Each microthread has an Instruction Pointer (IP) that points at code, and a register set, including a Frame Pointer (FP) that points at a Frame.

ProcessorLocal Mem
CodeMicrothreads
ProcessorLocal Mem
CodeMicrothreads
Stack framesStack frames
Global MemLocal pointers:Global pointers:Microthreads:
Frame Pointerand other registersInstruction Pointer

Fig. 2. P-RISC runtime state

There are two flavors of pointers. A Local Pointer is a normal address in local memory and is meaningful only within a processor. A Global Pointer identifies an arbitrary object in Global Memory or an arbitrary frame on any processor. We leave the exact coding of Local vs. Global pointers unspecified.