COMPUTER ORGANIZATION for beginner and a

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Table of contents:
1. Introduction
2. Data flow between CPU, memory, and I/O devices
3. Central Processing Unit
4. Arithmetic Logic unit
5. Communication inside a computer.
6. Interconnection Of Units
7. System bus types
8. Processing of information
9. Memory and types
10. Input and output devices
11. Conclusion

Introduction:
In computer science and engineering computer architecture is the practical
art of selecting and interconnecting hardware components to create
computers that meet functional, performance, and cost goals and the formal
modeling of those systems.
The functional blocks in a computer are of four types:
1. Central Processing Unit
2. Memory
3. Input Unit and Output unit

Data flow between CPU, memory, and
i/o devices
Auxilliary Storage
(Backing Storage)
To Supplement main storage
Memory
Input
Unit
Control Unit ALU
Output
Unit
Registers
Processor
Data Path
Control Signals

Central Processing Unit (CPU)
The CPU or the microprocessor (or simply processor) is referred as the brain
of a computer system.
CPU consists of three main subsystems, the Control Unit (CU), the
Arithmetic Logic Unit (ALU), and the Registers.
Speed of the computer system is defined by the architecture of the processor
being used.

Arithmetic Logic unit
The ALU contains electronic circuits necessary to perform arithmetic and
logical operations.
The arithmetic operations are ADD, SUBSTRACT, MULTIPLY, DIVIDE, etc.
The logical operations include COMPARE, SHIFT, ROTATE,AND, OR, etc
The control unit analyses each instruction in the program and sends the
relevant signals to all other units – ALU, Memory, Input unit and Output unit

Communication inside a computer

Communication inside a
computer.
A computer program consists of both instructions and data.The program is
fed into the computer through the input unit and stored in the memory.
In order to execute the program, the instructions have to be fetched from
memory one by one.
This fetching of instructions is done by the control unit.
After an instruction is fetched, the control unit decodes the instruction.

Communication inside a computer.
After an instruction is executed, the result of the instruction is stored in
memory or stored temporarily in the control unit or ALU, so that this can be
used by the next instruction.
The results of a program are taken out of the computer through the output
unit.
The control unit,ALU and registers are collectively known as Central
Processing Unit (CPU)

Interconnection Of Units
A computer program consists of both instructions and data.
The program is fed into the computer through the input unit and stored in
the memory.
In order to execute the program, the instructions have to be fetched from
memory one by one and store it into registers (working memory) for
processing.
This fetching of instructions is done by the control unit.

Instruction Cycle
Instruction are fetched and
executed by the control unit
one by one.The sequences
involved for the fetch of one
instruction and its execution are
known as instruction cycle.

Inter-connections of units.
Set of wires used for interconnection is known as system bus which carry
group of bits (information) in a controlled manner.
It is further divided into three logical units, namely the address bus, the data
bus, and the control bus.

System Buses Types
• Data Bus: The data bus is used when any unit is sending data, instruction or
command code to some other units.
• Address Bus: The address bus is used when one unit is sending address
information i.e. location of the data residing in the memory to another unit.
• Control Bus: The control bus is responsible for making CPU, memory, and
I/O devices work together as a functional system, carrying signals that report
the status (ready, not ready) of various units.

Interconnection of Computers Units
via System Bus
CPU
Input and
Output(I/O)
Units
Memory
Unit
Data Bus
Address Bus
Control Bus
System
Bus

Interconnection of Computers Units via Bus
Shows how the system bus interconnects the processor, memory and I/O
devices.
Both processor and memory units hold a bi-directional relationship with
the control and data bus.

Processing of Information
The bus is common to all the units in the computer. Before sending some
information on the bus, an unit should verify whether the bus is free or
occupied with some communication started by some other unit.
CPU is the bus master in a computer that decides who should control the bus
when more than one unit wants the bus at the same time.
 A unit that needs the bus makes a request to the CPU and waits for sanction.
Till the CPU issues a sanction, the requesting unit does not attempt to use the
bus.

Registers
It is a special temporary storage location within the CPU.
Registers quickly accept, store and transfer data and instructions that are
being used immediately.
To execute an instruction, the control unit of the CPU retrieves it from main
memory and places it onto a register.
The typical operations that take place in the processing of instruction are part
of the instruction cycle or execution cycle.
The instruction cycle refers to the retrieval of the instruction from main
memory and its sub sequence at decoding.

Control Unit
It is responsible for directing and coordinating most of the computer system
activities.
It does not execute instructions by itself. It tells other parts of the computer
system what to do.
It determines the movement of electronic signals between the main memory
and arithmetic logic unit as well as the control signals between the CPU and
input/output devices.

Memory
Memory is the computer's electronic scratchpad or local store in computer
terminology.
Used for temporary storage of calculations, data, and other work in progress.
Two types: Primary and Secondary
Primary memory or the main memory is part of the main computer system.
The primary memory itself is of two types.
The first is called random access memory (RAM) and the other is read only
memory (ROM).

Random Access Memory (RAM)
The processor directly stores and retrieves information from it.
Memory is organized into locations. Each memory location is identified by a
unique address.The access time is the same for all locations.
It is volatile: when turned off, everything in RAM disappears.
Two types:
1. Dynamic Random Access Memory (DRAM):
2. Static Random Access Memory (SRAM):

Types of RAM
1. Dynamic Random Access Memory (DRAM):
 This type of RAM retain the content of any location only for a few
milliseconds.Within that period, each location must be written again with the
same contents.This is known as refreshing.
2. Static Random Access Memory (SRAM):
 This type of RAM preserves the contents of all the locations as long as the
power supply is present. SRAM is generally included in a computer system by
the name of cache.

Read Only Memory (ROM)
Data stored in ROM cannot be modified, or can be modified only slowly or
with difficulty, so it is mainly used to distribute.
The instructions in ROM are built into the electronic circuits of the chip
which is called firmware.
Random access in nature and non-volatile.

Types of ROM
• Programmable read-only memory (PROM), or one-time programmable ROM can
be written to or programmed via a special device called a PROM programmer.
• Erasable programmable read-only memory (EPROM) can be erased by exposure
to strong ultraviolet light then rewritten with a process that again needs higher
than usual voltage applied.
• Electrically erasable programmable read-only memory (EEPROM) is based on a
similar semiconductor structure to EPROM, but allows its entire contents (or
selected banks) to be electrically erased, then rewritten electrically, so that they
need not be removed from the computer

Flash Memory
Modern type of EEPROM invented in 1984.
Random access memories and are non-volatile.
Use one transistor per memory cell and come in capacities ranging from 1 MB
to 32 GB by the year 2007.
The read time is much smaller (tens of nanoseconds) compared write time
(tens of microseconds).

Cache Memory
High speed memory kept in between processor and RAM to increase the data
execution speed.
Kept near to the processor.
Major reason for incorporating cache in the system is that the CPU is much
faster than the DRAM and needs a place to store information that can be
accessed quickly.
Cache fetches the frequently used data from the DRAM and buffers (stores) it
for further processor usage.

Input and Output
Devices
INPUT DEVICES
• Any peripheral used to provide data
and control signals to an information
processing system such as a
computer or other information
appliance.
• Examples: Keyboard, Mouse
OUTPUT DEVICES
Any piece of computer hardware
equipment used to communicate the
results of processed data to the user.
Examples: Monitors, Printers,
Speakers, etc.

Conclusion
• Computer organization and architecture is defined as the science of selecting and
interconnecting hardware components to create computers that meet
functional, performance and cost goals.
• The central processing unit is the brain of the computer system where all the
computing is done. It consists of three main components, the control unit (CU),
the arithmetic logic unit (ALU) and the registers.
• The control unit controls the Input/Output devices and transfer of data to and
from the primary storage.

References
• Wikipedia.org
• Google.com
• Seminarppt.com
• Studymafia.org

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