4. Multicore Machines

Multicore machines are an extension of the single core personal computer that include several processors (cores) and a shared memory. As such, they are suitable for running parallel programs, including ParC, that use shared memory. Multicore machines replace single processor personal computers and are thus widely used. In this work we will use the term “core” instead of processor or CPU to indicate that several cores are packed in a single chip or actually in one die, functioning as a multi-processor machine. Basically, the parallelism available in multicore machines is used by the operating system to execute several unrelated processes in parallel (e.g., running two compilations and a web search on different cores). We will demonstrate that multicore machines can be used to execute parallel programs efficiently, programs that spawn many threads all communicating through shared memory. However, as an extension of a single core machine designed for personal computers, the mechanism using the shared memory is not as effective as it would have been had it been designed from scratch as a parallel machine. In fact, the shared memory of multicore machines is basically a simulation of shared memory over the single port memory module of the single core personal computer. Thus, it is important to understand how the shared memory of multicore machines works in order to determine how ParC can be implemented and used by multicore machines.