Question

Question 2 (a) The Von Neumann Architecture contains four main components: Central Pro- cessing Unit (CPU), Main Memor, Secondary Storage and I/O Units. Explain [8 marks] (b) Give an example of a program instruction that could cause a stack overflow. [2 marks] [Total for Question 2: 10 marks] the role of each of these components. You can either provide code or an english description.

Answer 1

Von Neumann architecture :

This is simply a design model used for a stored-program digital computer. There are four major components that helps in functioning of this model given as follows :

1. Central processing Unit(C.P.U)
2. Main Memory
3. Secondary memory/storage
4. Input-output unit.

1. The functions of all of these components in Von Neumann Architecture is given as follows :

1. Central Processing unit:

C.P.U is basically an electronic unit whose responsibility is to execute the instructions given in the computer program. It was also referred to as processor, it contains ALU, CU and few registers. The components that together contribute in the working of C.P.U are as follows :

• Control Unit
• Arithmetic and Logic Unit
• Registers like Ac, MDR, CIR, PC, MAR.

2. Main Memory Unit :

The main memory in Von Neumann architecture consists of set of registers with different functionalities. The registers used in main memory is given as follows :

• Accumulator : All the calculations that are carried by ALU is stored in accumulator.

• PC (Program counter) : The track of locations of next memory instruction to be handled is kept in PC.

• MAR (Memory address register) : The memory location of the instructions which needs to be stored into the memory are stored in MAR.

• MDR (Memory Data Register) : The memory location of the instructions that are fetched from memory which needs to be transferred into the memory are stored in MDR.

• IBR (Instruction Buffer Register) : There are instructions that are not on priority and there is no need to execute these instructions immediately. These instructions are stored in IBR.

• CIR (Current Instruction Register) : The instructions which are fetched recently and are waiting to get executed are stored in CIR.

3. Secondary Storage :

• Secondary storage acts as a core functional component of computer. Its major role is to stores digital and media information. It has lower price per MB as compared to the main memory.

• There can be various forms of secondary memory with being the CD-ROM the most common form.

4. I/O unit:

• I/O units consists of a set of input and output devices that are used to give input and obtain outputs from a system. Input devices also acts as an interface between the computer and output devices.
• The role of input units is to give input to the system for processing. Some of the examples of these output devices are keyboard, scanners, mouse etc.
• The role of output unit is to display the result or data obtained by performing various operations that are being performed in the system. Some of the examples of these output devices are monitor, printer etc.

2. Example is given as follows :

• A stack overflow occurs when your program has used more memory than it was supposed to used.
• One of the most common cause of stack overflow is infinite recursion which is also known as deep recursion. In this, the program functions calls itself again and again and it ends up using more storage space to store its variables than it was allocated to it.
• One other way to get a stack overflow in programs of C or C++ is to declare some variable that are enormous
• e.g. :- char Array[100000000];