KTF11-A memory management chip
From Computer History Wiki
The KTF11-A memory management chip is an optional chip for PDP-11 CPUs which use the F-11 chip set. It implemented the standard PDP-11 Memory Management (but only the simplified subset).
The KEF11-A floating point chip option requires the KTF11-A, since the floating point registers are actually in the KTF11-A (the reason is unknown; the KEF11-A is microcode, but there are enough pins for both the data bus, and the microcode bus).
The KTF11-A chip was the DC304, DEC part number 21-15542-0n (where n is a digit giving the revision; 0 and 1 have been seen).