This document provides an overview of the functional components of a computing system, including the input, central processing, memory, and output units. The central processing unit (CPU) is made up of three main components: the arithmetic logic unit (ALU) which performs calculations and logical operations, the control unit which controls data flow and operations, and memory registers for temporary storage. The memory unit stores data and instructions using technologies like static RAM and dynamic RAM. Together these components allow a computer to process input according to stored instructions and provide output.

1. ECE 3004 – Computer
Organization and
Architecture

2. Module 1: Introduction
to Computing Systems
Dr. J. Florence Gnana Poovathy
Assistant Professor (SG – 1)
SENSE, VIT

3. Functional Components of a
Computing System
• Three units of a computer
• Input unit – takes input from the user
• CPU – processes that input
• Memory unit – stores data and instructions while
processing
• Digital computer – a programmable machine that
reads the binary data, processes that data and
communicates the binary data as output

4. Functional Components of a
Digital Computer
Input Output
ALU
CU
MU
CPU

5. Input Unit
• Consists of input devices attached to the computer
• Takes input, converts to binary form that the
computer understands
• Ex???

6. Central Processing Unit (CPU)
• Processes the received input
• Called the brain of the computer because it is the
control center of the computer
• Fetches instructions from memory
• Uses these instructions to perform the jobs given by
the user
• Data is fetched either from input device or from
memory
• Three main components
• Arithmetic and logic unit (ALU)
• Control Unit (CU)
• Memory unit (MU)

7. Arithmetic and Logic Unit (ALU)
• Perform mathematical calculations
• Takes logical decisions
• Arithmetic operations
• Addition
• Subtraction
• Multiplication
• Division
• Logical operations
• Comparisons
• AND, OR etc.

8. How ALU works?
• Information is processed in terms of binary digits
• Transistor switches are used since there are only
two possibilities – open or close

9. Continued…
• Open transistor – no current flow – 0
• Closed transistor – current flow present – 1
• Operations can be done by connecting multiple
transistors
• One transistor can be programmed to control
another
• Ex. Turn the first transistor ON or OFF according to the
state of the second transistor
• This arrangement is called gate

10. A simple gate – NOT gate
• Uses only a single transistor
• Other gates – OR, AND, XOR etc.

11. Control Unit
• Controls the data flow in and out of the processor
• It also controls the operations of the ALU, memory
and I/O devices
• It carries out the instructions stored in the memory
• It decodes those instructions, interprets it and
sends control signals to the I/O devices

12. Memory registers
• Temporary unit of storage in CPU
• Data stored here are directly used by the processor
• Different sizes – 16, 32,64
• Functions of register
• Storing data
• Storing address
• Instruction locations
• User registers can be used to store data and
address by the user
• Accumulator is the main register – it always has an
operand that would be used by the ALU

13. Memory
• Used for storage of data and instructions
• Internal memory is divided into many locations each of
which has a dedicated address
• So entire memory need not be searched
• When program is executed, the data is copied in the
internal memory and is stored there till the execution is
over.
• This is called RAM
• SRAM – Static RAM – has circuits that retain the data as
long as the power is ON – made up of flip-flops
• DRAM – Dynamic RAM – stores binary data in the form
of electrical charges using capacitors – data is lost after
a period of time and hence capacitors must be charged
periodically

14. Output unit
• Consists of output devices attached to the
computer
• Converts binary data from CPU to human-
understandable form
• Ex???