**Machine type**: Shared-memory multi-vectorprocessor.

**Models**: Y-MP T90.

**Operating system**: UNICOS (Cray Unix variant).

**Compilers**: Fortran, C, C++, Pascal, ADA.

**System parameters**:

**Performance**:

**Note**: The and values as given above stem from a 16
processor T90 (T916).

The T90 is the successor of the the Cray Y-MP C90 and in almost all respects the machines are similar. As in the C90, the number of arithmetic vector pipe sets is four. The performance of a full T90 CPU is slightly less than four-fold that of a maximal C90 system. This is brought about by lowering the clock cycle from 4.1 to 2.2 ns and by doubling the number of CPUs from 16 to 32.

The machines from Cray Research Inc. are at this moment the only ones with a memory bandwidth as seems optimal for vector processors: two operands can be loaded and one result can be stored in one cycle for each pipe set. For the C90 this meant that the relative bandwidth to the CPUs had to be doubled from 24 to 48 bytes/cycle. This has indeed been accomplished and observed results indicate that for the C90 the performance scales up with the clock cycle and the number of functional units.

The Cray Y-MP T90, C90, and M90 systems do not have separate scalar processors but scalar- and vector code have to share the same functional units. Theoretically, the absence of separate scalar processors might impair the throughput speed, however, in practice the drawbacks seem rather limited.

Tue May 28 14:38:25 PST 1996