cooperative scheduling algorithm : the program explicitly yields the CPU for the next task
same as old operating systems: MacOS 9, Windows 95 running legacy 16-bit code, MS-DOS and so on.
advantages: easy to adapt existing languages and systems to the method; highly efficient in throughput; allows you to "pack" lots of work into a single process.
weakness: if one of the tasks in the task queue monopolizes the CPU, hangs or blocks, then the impact is worse throughput, higher latency, or a deadlocked server.
Erlang runtime:
preemptively: An internal funcall counter measures "reductions" and once 2000 of these has been used, the process is forced off the CPU and the next one is switched in.
same as modern time-sharing operating systems: UNIX, Windows NT+
