This figure shows the Extended-Computer++ model which adds an OS multiprogramming module to the Extended Computer model. The OS module introduces five new instructions, a FIFO process queue implemented using hardware registers, a time-slice interrupt circuit that performs process preemption, and an OS initialization and multiprocessing software placed at the beginning of RAM.

A model builder can choose to implement either one or both of the extension modules (i.e., input interrupt processing, OS multiprogramming function).

(Construction time: 26 to 31 hours).