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The Cray Y-MP C90

Machine type: Shared-memory multi-vectorprocessor.
Models: Y-MP C90.
Operating system: UNICOS (Cray Unix variant).
Compilers: Fortran, C, C++, Pascal, ADA.

System parameters:


The C90 is the successor of the the Cray Y-MP and in many respects the machines are similar. However, in the C90 the number of vector pipe sets is doubled with respect to the Y-MP models. Therefore, the performance of a C90 CPU is trice that of a Y-MP CPU, a factor 1.5 because of the lower clock cycle and an additional factor of 2 because of the doubling of the functional units. The doubling of the number of CPUs makes the maximal C90 6 times faster than the fully configured Y-MP or Y-MP M90 (see below).

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, 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 Nov 14 15:39:09 PST 1995