Parallel communication a time. If both channels operated at the same clock speed, the parallel channel would be eight times faster. A parallel channel may have additional conductors for other signals, such as a clock signal to pace the flow of data, a signal to control the direction of data flow, and handshaking signals. Parallel communication is and always has been widely used within integrated circuits, in peripheral buses, and in memory devices such as RAM. Computer system buses, on the other hand, have evolved over time: parallel communication was commonly used in earlier system buses, whereas serial communications are prevalent in
NAS Parallel Benchmarks serial versions of the benchmarks consistent with the parallel versions and defined a problem size "Class W" for small-memory systems. NPB 2.4 of 2002 offered a new MPI implementation and introduced another still larger problem size "Class D". It also augmented one benchmark with I/O-intensive subtypes. NPB 3 retained the MPI implementation from NPB 2 and came in more flavors, namely OpenMP, Java and High Performance Fortran. These new parallel implementations were derived from the serial codes in NPB 2.3 with additional optimizations. NPB 3.1 and NPB 3.2 added three more benchmarks, which, however, were not available across all implementations;