[1gn1t10n]

On an Intel i5-2520M (4 threads [1]) it reported 5 usable worker threads.

As I see from others, the result reported by core-estimator is spot on N+1, where N is the number of virtual cores [2].

It might be a coincidence, but this is exactly the number of jobs one would give to make when compiling [3].

Knowing N helps to be efficient when spawning threads (avoiding swamping or starving cores).

[1] http://ark.intel.com/products/52229/ [2] as reported for example by /proc/cpuinfo on Linux [3] i.e. "make -j5"