This article is from the storage FAQ part2, by Rodney D. Van Meter with numerous contributions by others.
32-bit transfers at 25 MT/sec., 100 MB/sec. High Performance Parallel Interface is a unidirectional channel, i.e. you have to have an OUT cable and and IN cable for bidirectional transfers (you could have just one, if it's a read-only device like a scanner or write-only like a frame buffer). HiPPI is not a shared bus, but its frames can be switched through a crossbar switch (Network Systems is the premiere vendor). HiPPI is used for supercomputer-to-supercomputer networking (TCP/IP, no less), for RAID arrays (from Maximum Strategy, IBM and others), tape drives (Sony ID-1 drive), frame buffers and increasingly workstations (SGI and IBM support HiPPI, and 3rd-party Sbus cards exist for Sun). Due partly to the high overhead of HiPPI connections, many devices have elected to separate the control path from the data path. A common control path in that case is ethernet. Good resources from the HiPPI Networking Forum on the web at http://www.esscom.com/hnf/.