Info from HESS Duane: Memory board, shows the middle card pulled out. The unit has 800 program steps and 60 memories. So the program memory must be in the foreground and data to the back. All memory chips, data or program, are HD3543. If I recall info from the web the 300 can have an internal maximum of 100 data memories and 1000 program steps. So 10 locations each on the board makes sense.