14.2 What concurrency really means
In a small computer, with a single processor and a single core, all evaluations are serialized through the one and only core of the processor. The OS will interleave multiple processes and multiple threads through clever time-slicing arrangements to make it appear as if things are happening concurrently.
On a computer with multiple CPUs or multiple cores in a single CPU, there can be some actual parallel processing of CPU instructions. All other concurrency is simulated through time slicing at the OS level. A macOS X laptop can have 200 concurrent processes that share the CPU; this is many more processes than the number of available cores. From this, we can see that OS time slicing is responsible for most of the apparently concurrent behavior of the system as a whole.
14.2.1 The boundary conditions
Let’s consider a hypothetical algorithm that has a complexity described by O(n2). This generally means two nested for statements, each of which...
