The Von Neumann Architecture

The basic funcion penomed by a computers the executon of a progam.A program is a set of machine instructions. An instruction is a form of control code, which supplies the informaton about an opeaton and the data on which the opeation is to be performed. A typical von Neumann machine consists of five functionality independent unit
(i) Input unit
(ii) Output unit
(iii) Arithmetic and logic units
(iv) Contol unit
(v) Memory unit

Input Unit:
Computers accept coded informaton through input units, which read the data. The most common input device is the keyboard.  Whatever the key is pressed,  the corresponding letter or digit is translated into it's corresponding code and sent to the processor. There are many other kinds of input devices like
(i) Modem
(ii) mouse
(iii) joystick

Output Unit:
Output unit sends proceed result to outside world. The familiar example of such device is a printer. There are many odher kinds of output devices like:
(i) video teminal
(ii)Floppy drive
(iii) CD-drivers ra
(iv) Modem

Arithmetic and Logic Unit (ALU):
Arithmetic and logic operation like multiplication,  addition, division are performed by ALU.  Operands  brought into the ALU. where the necesary opeation is performed.

1.1.4 Control Unit: opertions of ALU, memory and input and output unit are coordinated and controlled by the control unit. control unit sends control signal to other units.  Data tansfer between processor and memory are  controlled by te control unit through timing signal.

Memory unit:
Main memor is needed in a computer to store instructions and the data at the time of program execution. It was pointed out by Von Neumann that the same memory can be used for storing data's and instuction. The memory unit stores all information in a group of memory cells as binay digits. Each memory location has a unique address and can be addressed independently. The contents of the desired memory locations are provided to the central processing unit by refering to the address of the memory location. The amount of information, which can be transferred between CPU and memoy, depends the size of the BUS connecting the two.