1975. The LSI-11 was a microprocessor-combo, implemented on a single quad-height board (KD11-F), that used the new LSI-11 bus (later known as the qbus), a (then) 18-bit wide system bus.
The LSI-11 chipset was later marketed as "WD-16" by its manufacturer: Western Digital. It consists of four 40-pin DIP IC's: the 23-002C4 control chip, the 21-11549-01 (or -00) data chip, and two microms for the instruction set: 23-002B5 and 23-001B5. The fifth socket could be used with the KEV11 EIS/FIS option (23-003B5), or with the KUV11-AA WCS (Writable Control Store) option, which is a quad-height module, connected to this socket via a cable.
The normal revisions of the module (M7264) had 8 KByte on-board memory, the M7264-YA version lacked it. You can find more hardware information about the LSI-11 CPU's here.
The LSI-11 was heavily marketed for OEM usage, and was superceded by the LSI-11/2, which was smaller (a double-height module), consumed less power, but lacked the WCS option and on-board memory.
Both boards were also used as the CPUs of PDP-11/03 systems. The LSI-11 and LSI-11/2 offered 83 standard PDP-11 instructions, with 8 optional EIS/FIS instructions (KEV11 option), 32KW addressing range, MicroODT (Octal Debugging Technique on the console) and one interrupt level.