When someone says "running the parallel version on a single CPU" they usually mean running the parallel version with 1 thread on 1 CPU. Comparing that to the se

When someone says "running the parallel version on a single CPU" they usually mean running the parallel version with 1 thread on 1 CPU. Comparing that to the sequential (non-parallel) version allows you to measure the baseline overhead cost of parallelization. There are also non-baseline overhead costs of parallelization, which usually come in the form of synchronization overhead between threads or processes.