The EDSAC was the first truly operational computer and certainly has "reduced" instruction set; actually, it is the accumulator-based ISA, not load-store GPR as we relate with the term. In early days deep significance of 'stored program computer' was that instructions were simply numbers stored in memory, which could hence be operated on. Though, this conceptual power obscured practical significance of certain simple aspects of instruction set which could eliminate requirement for self-modifying code. It finally disappeared for performance reasons-programming clarity motivations came later.

a. Write down simple (closed) subroutine sum(A,n) to sum the array of n integers and return result un EDSAC using "initial orders -- second form" described in paper. Also illustrate the snipet of code to call it and access result.

b. Write down recursive subroutine fact(n) which calculates factorial function.