FPP-12 -- The PDP-12 Floating Point Unit

S M L XL

This is an FPP-12A, a floating point unit for the PDP-12 minicomputer. It is 32 columns of cards by 12 rows (384 card positions, although not all are occupied). (A normal FPP-12 has a 12-bit exponent and a 32-bit mantissa; the FPP-12A was upgraded to a 64-bit mantissa. The last four rows of modules were added to make the FPP-12 into an FPP-12A.)

The FPP-12 uses some "exotic" M-series cards:

Card	Function
M107	(unlabeled)
M127	2-2-2-3 AND NOR Gate
M133	10-2 Input NAND Gates (implemented via 9 x 74H00s)
M135	3 Input NAND Gate (implemented via 3 x 74H10s)
M139	3-8 Input NAND Gates (implemented via 3 x 74H30s)
M155	General purpose 24-pin chip carrier; effectively allows you to kludge a 24-pin chip onto the backplane, with the usual 74-series assumption about +5V and GND. Causual inspection of the FPP-12 shows them used with 74154 (4-to-16 line decoder) chips. These are at the top right of the picture.
M172	2 x 9 Data Mixer
M178	8 x 6 Data Mixer
M190	4 bit arithmetic logic module (using a 74181)
M191	(unlabeled) uses 2 x 74182
M205	5 D-type Flip Flops
M238	(unlabeled) uses 2 x 74193
M245	General purpose 2 x 16-pin chip carrier; allows you to kludge 2 16-pin chips onto the backplane.
M611	High Speed Power Inverter
M734	I/O Input Bus Multiplexer

I actually have two of these; a FPP-12 in my PDP-12, and this one (an FPP-12A) in a stand-alone rack.