CS100 - Assignment 4 (Computing components)

(Section 001, Fall 2007)

The questions carry equal weight. Please show the computations leading to the result. Show all your work for full credit!

1. Describe the components in a von Neumann machine.

2. Describe the fetch-decode-execute cycle of the von Neumann machine.

3. Assume a simple processor with three registers: program counter (PC), instruction register (IR), and accumulator (AC). Assume the processor has the following instruction set:

   operation code	action
   001 xxx	load the value from memory address xxx into AC
   010 xxx	store the value of AC into memory location xxx
   011 xxx	add the value of memory location xxx to AC
   110 xxx	jump to memory location xxx
   111 000	halt execution

   Let the content of the memory be:

   address	content
   000	001 110
   001	011 111
   010	010 101
   011	111 000
   100	010 000
   101	000 000
   110	000 011
   111	000 100

   1. Assuming that execution starts with PC=000, write the content of the PC and IR registers when execution halts. Describe which part of the memory is used to store instructions and which is used to store data.

   2. Assuming that execution starts with PC=000, describe the operations that will be performed by the CPU and write the content of all the memory cells when execution halts.

   3. Describe what happens if by accident execution resumes with PC=100 and write the content of all the memory cells when execution halts. Explain the disadvantage of the von Neumann architecture in this respect.