The only Power based supercomputers I can think of are all from IBM. Does any other vendor use them?
Power CPUs tend to power either iSeries (latest iteration of AS/400 - System38 etc) systems or AIX based. The large AIX systems use lots of CPUs, cores and typically vPars - but I wouldn't call them supercomputers. Disk I/O is generally FC attached SAN, i.e. performance is achieved through off-loading. A typical SAN array contains gigabytes of caching memory, CPUs on each disk drive with yet more RAM and multiple optical FC links to each node.
Power CPUs tend to power either iSeries (latest iteration of AS/400 - System38 etc) systems or AIX based. The large AIX systems use lots of CPUs, cores and typically vPars - but I wouldn't call them supercomputers. Disk I/O is generally FC attached SAN, i.e. performance is achieved through off-loading. A typical SAN array contains gigabytes of caching memory, CPUs on each disk drive with yet more RAM and multiple optical FC links to each node.