0th gen: P880  (1970/1971)

1st gen: P850, P855 and P860 (1971)

 P850: 2k of 16 bit words
 P855: 4k 16 bit words up to 32k 16 bit words 1.2 us (core) memory
 P560: 4k 16 bit words up to 32k 16 bit words 0.84 us (core) memory

2nd gen: P852, P856 and P857 (1976) using core memory

 P852: 95% compatible with the P855 (except for channel IO and interrupt system, 
       and some instructions were simulated)
 P856: extended instruction set
 P857: extended instruction set, a floating point option and memory 
       up to 128k 16 bit words and a memory management unit option 
       to operate on memory bigger than 32k words

3rd gen: P851, P853/854 and the P858/859 (1981/1982) using DRAM more than 32 k x 16
         required a separate MMU chip.

 P851: single board LSI version of the P852 based on SPC16/10
 P853: memory upto 128k 16 bit words "small" machines on euro cards based on 
       SPC16/10, SPC16/11, SPC16/12
 P854: memory upto 512k 16 bit words "small" machines on euro cards based on 
       SPC16/10, SPC16/11, SPC16/12
 P858: memory upto 128k 16 bit words installation in a 19 inch rack based on 
       SPC16/10, SPC16/11, SPC16/12
 P859: memory upto 512k 16 bit words installation in a 19 inch rack based on 
       SPC16/10, SPC16/11, SPC16/12

The 3rd generation models were based on the SPC16/10 or the later SPC16/20 processor.
These processor allowed for the separate firmware and software memory banks.