Many programmers have avoided use of multiple threads, because they can be hard to use correctly and are often unnecessary on single-processor systems. Others have started using them without a full understanding of how the memory model of a multithreaded program can differ from that of a single-threaded program. For the foreseeable future, increases in computing power will largely be due to increased parallelism (multiple processor cores and multiple threads scheduled per core) and not by increases in the speed at which individual threads are executed. Therefore it is important that programmers learn how to write reliable multithreaded code. The portability of Debian raises particular challenges, as different architectures implement different memory models in multiprocessor configurations.