In comparison to 10 years ago the processor scene has become drastically different. While in the period 1980–1990, the proprietary processors and in particular the vectorprocessors were the driving forces of the supercomputers of that period, today that role has been taken over by common off-the-shelf processors. In fact there is only one companies left that produces vector systems (NEC) while all other systems that are offered are based on RISC CPUs or x86-like ones. Therefore it is useful to give a brief description of the main processors that populate the present supercomputers and look a little ahead to the processors that will follow in the coming year. Still, we will be a bit more conservative in this section than in the description of the systems in general. The reason is processors are turned out at a tremendous pace while planning ahead for next generations takes years. We therefore tend to stick to the really existing components in this section or when already a β version of a processor is being evaluated.
The RISC processor scene has shrunken significantly in the last few years. The
Alpha and PA-RISC processors have disappeared in favour of the Itanium processor
product line and, interestingly, the MIPS processor line that appeared and
disappeared again as they were used in the highly interesting SiCortex systems.
Unfortunately SiCortex had to close down recently and with it the MIPS
processors again. In addition, the Itanium processor is not used in HPC anymore
while IBM has terminated to offer systems with the PowerPC processor (except a
modified version in its BlueGene system family).
The notion of "RISC processor" alltogether has eroded in the sense that the processors that execute the Intel x86 (CISC) instruction set now have most of the characteristics of a RISC processor. Both the AMD and Intel x86 processors in fact decode the CISC instructions almost entirely into a set of RISC-like fixed-length instructions. Furthermore, both processor lines feature out-of-order execution, both are able to address and deliver results natively in 64-bit length, and the bandwidth from memory to the processor core(s) have become comparable to those of RISC processors. A distinguishing factor is still the mostly much larger set of registers in the RISC processors.
Another notable development of the last few years are the placement of more than one processor core on a processor chip and the introduction of various forms of multi-threading. We will discuss these developments for each of the processors separately.
There are two processors one perhaps would expect in this section but are nevertheless not discussed: the Godson 3B and the Itanium Tukwila processors. The first processor, a Chinese one, based on the MIPS architecture, is not available in any machine that is marketed now or in the near future. The newest Itanium processor does not play a role anymore in the HPC scene and is therefore also omitted.