<An FPF11 can be used with a KDF11-B (11/23+), which is a Qbus <machine. It can also be used in an 11/24, it derives only <power from the bus (if I remember correctly). Correct, I have one. <I would suspect that it might also work with an 11/23 (KDF11-A), <since it has the same chip location for Floating point as the <11/23+, but I've never confirmed this. It works with all of the 11/23 series (Q and U,). Jumpers configure power for either U or Q and much be checked before inserting. What it is is a faster version on a quad board for the FPU chip. If you crunch numbers on 11/23s or 11/24s it's a must have. FYI, It's a raft of 2901s and some microcode to emulate the FPU chip. It's faster as all the data paths internally (to the board) are wider. Allison