CPU
control unit      
accumulator      
ALU      
       
pc cir mar mdr
       

An application has been loaded into RAM. Along with application data, a set of instructions will be processed.

All of the instructions and all of the data exist at unique memory locations in RAM.

The following simulation gives an idea of what a cpu has to do to add two numbers together.

address bus data bus
↓ ↕
RAM
address instruction
#100 LOAD #15
#101 ADD #16
#102 STORE #18
address data
#15 3
#16 9
#17 0
#18 0