This article is from the storage FAQ part2, by Rodney D. Van Meter with numerous contributions by others.
An effort aimed at reaching 6400 Mbps (800 Mbytes/sec.) around the end of 1996. From rev 0.15 of the HIPPI-6400-PH specification, dated March 4, 1996, ftp'ed from ftp.network.com:X3T11/hippi/hippi-6400-ph_0.15.ps. (ftp://ftp.network.com/X3T11/hippi/hippi-6400-ph_0.15.ps.) Looks like the copper interface will be a cable with 44 micro-coax conductors, 22 in each direction. That's 16 data, 4 control, clock, and frame. A micro-packet is 32 data bytes and 64 bits of control information. I guess this means they're planning on 400 Mbps on each data line. The fiber variant uses 12 multimode fibers (in each direction, I presume, though it doesn't seem to say that): 8 data + 2 control + frame + clock, so presumably 800 Mbps on each fiber. Cable lengths in both cases TBD.