This document provides an overview of basic computer organization and structure. It defines key terms like computer, organization, and functional units. The main functional units of a computer are described as the input, output, control unit, ALU, and memory. Basic operational concepts like fetch-execute cycles and connection between processor and memory via registers like the program counter, memory address register, and memory data register are explained. Read and write operations to memory are demonstrated. Finally, an example program is used to illustrate the overall operating steps of a computer from program loading to instruction execution.

1. Chapter 1:
Basic Structure of Computers
COMPUTER ORGANIZATION
Mrs.S.SUMATHI,
Assistant Professor, Dept. of IT,
EMG Yadava Women’s College, Madurai – 14
sumathi.emg@gmail.com

2. Outline…..
 Introduction
 Functional Units of a Computer
 Basic Operational Concepts
 Connection between the Processor and Memory
 Read and Write Operation
 Operating Steps
 Conclusion

3. Computer
 Computer is an electronic device that receives
input, stores or processes the input as per user
instructions and provides output in desired
format.

4. Organization
 An Organization is a group of people who work
together and achieving a goal or something.
 It also refer to a system of arrangement or a
structure for classifying things.

5. Computer Organization
 The computer organization is concerned with the
structure and behaviour of digital computers.
 The main objective of this subject to understand the
overall basic computer hardware structure.
 A computer system is consists of an inter-related set
of components.
 The system is best characterized in terms of
 structure- the way in which they are interconnected
and
 function- operation of individual component.

6. Components of a Computer
 Control Unit, arithmetic and logic unit and
memory are together called the Central
Processing Unit or CPU.
 Computer devices that we can see and touch are
the hardware components of a computer.
 Set of instructions or programs that make the
computer function using these hardware parts are
called software.

7. Functions of a Computer
In general terms, there are four main functions of a
computer:
Data processing
Data storage
Data movement
Control

8. Input - Process – Output
Model
Simplest Workflow of Computer
 Computer input is called data.
 Processes that can be applied to data are of two types:
 Arithmetic operations.
 Logical operations.
 Raw facts and figures can be processed using arithmetic and
logical operations to obtain information.
 Output obtained after processing data.
Input Process Output

9. Basic Functional Units of a Computer

10. Basic Functional Units of a Computer
 Input Unit: Devices used to input data and information.
 Output Unit: Devices used to provide information to the
user in desired format.
 Control Unit: All devices or parts of computer interact
through the control unit.
 ALU: All arithmetic and logical operations take place.
 Memory: All input data, instructions and processes are
stored in the memory.

11. Basic Operational Concepts
 To perform a given task an appropriate program
consisting of a list of instructions is stored in the
memory.
 Individual instructions are brought from the memory
into the processor, which executes the specified
operations.
 Example:- Add LOC, R0
 This instruction adds the operand at memory

12. Add LOC, R0
This instruction requires the performance of several
steps,
 1.First the instruction is fetched from the memory
into the processor.
 2.The operand at LOC is fetched and added to
the contents of R0
 3.Finally the resulting sum is stored in the register
R0

13. Connection between the Processor and the Memory

14. Connection between the Processor and the
Memory
 The instruction register (IR):-Holds the instructions that is currently
being executed. Its output is available for the control circuits which
generates the timing signals that control the various processing elements
in one execution of instruction.
 The program counter PC:-This is another specialized register that keeps
track of execution of a program. It contains the memory address of the
next instruction to be fetched and executed.
 Besides IR and PC, there are n-general purpose registers R0 through Rn-
1.
 The other two registers which facilitate communication with memory are: -
 1.MAR –(Memory Address Register):-It holds the address of the
location to beaccessed.
 2.MDR –(Memory Data Register):-It contains the data to be written into
or readout of the address location.

15. Read Operation
Processor Memory
Control
Unit
MAR
MDR
Address - 1000
Read Signal
Data - operand 5
1000 5

16. Write Operation
Processor Memory
Control
Unit
MAR
MDR
Address - 1000
Write Signal
Data - operand 7
1000 7

17. Example Program
 Load LOC, R1
 Add R1, R0

18. Operating steps are
 1.Programs reside in the memory & usually get these through the Input unit.
 2.Execution of the program starts when the PC is set to point at the first
instruction of the program.
 3.Contents of PC are transferred to MAR and a Read Control Signal is sent to
the memory.
 4.After the time required to access the memory elapses, the address word is
read out of the memory and loaded into the MDR.
 5.Now contents of MDR are transferred to the IR & now the instruction is ready to
be decoded and executed.
 6.If the instruction involves an operation by the ALU, it is necessary to obtain the
required operands.
 7.An operand in the memory is fetched by sending its address to MAR & Initiating
a read cycle.
 8.When the operand has been read from the memory to the MDR, it is
transferred from MDR to the ALU.
 9.After one or two such repeated cycles, the ALU can perform the desired
operation.
 10.If the result of this operation is to be stored in the memory, the result is sent to
MDR.

19. Conclusion
 This presentation covers many aspects of
Computer Structure and operation.
 An overview of some important design and
operating concepts are presented.

20. THANKING YOU