Machine type: Shared-memory multi-processor.
Models: Challenge M, L, XL.
Operating system: IRIX (SGI's Unix variant).
Compilers: Fortran 77, C, C++ , Pascal.
System parameters:
Performance:
Note: Only 
and 
for a 20 processor Challenge are given.
The Challenge systems are shared-memory multiple-instruction multiple-data parallel (MIMD) computers. So, several different instructions can be going on at the same time using different data items in these instructions. All data are stored in a single shared memory from which the multiple processors draw the data items they need and in which the results are stored again. In most high performance systems the main problem is to provide the CPUs with enough data and to transport the results back at such a rate that they can be kept busy continuously. In this, the Challenge is no exception. The data is transported from the main memory to the CPUs by a central bus. The so-called POWERpath-2 bus is 256 bits wide and has a bandwidth of 1.2 GB/s. This is very fast as busses go but even then the data rates that are needed by the CPUs cannot possibly be fulfilled when no special provisions would exist. These provisions are present in the form of data and instruction caches for each of the CPUs.
The Challenge series uses MIPS R4400 RISC processors with a nominal peak speed of 75 Mflop/s (except in the M model which has one 50 Mflop/s processor).