LECTURE NO.03.pptx babsbsbsbsbsbsbsbsbsbbsbs

Introduction to ICT
• System Unit
• Components of System Unit

System Unit
• System Unit is a case that contains
electronic components of the computer
used to process data.
• It is made of metal or plastic to protects the
internal components from damage.
• All computers have a system unit. It is
available in variety of shapes & sizes.

System Unit
• System unit of a desktop computer stands
vertically (tower model).
• In laptop computers, keyboard and pointing
devices are built on the top of the system unit.
• System unit of a tablet is behind the screen.

System Unit
System
unit
System
unit
System unit

Components of System unit
• Mother Board
• Central Processing Unit (CPU)
• Memory
• Ports
• Buses
• Bays
• Power Supply and Battery

Motherboard
• Motherboard
– Is also known as system board or main board.
– Is a communication medium for the entire
computer system.
• All components of the computer are connected
to the motherboard.
• It also enables the user to attach different
devices to it such as keyboard, printer and
scanner.

Central Processing Unit (CPU)
• CPU also known as processor is the brain of a computer.
• All computers must have a CPU, as a computer cannot
work without it.
• CPU is located on the motherboard and carries most of
the work of a computer.
• CPU
– Performs all operations on data according to the given
instructions.
– Executes instructions and tells other parts of computer what
to do.

• All functions of processor usually are on a single chip
in personal computers.
• A single-core processor is a processor with a single
core on a chip.
• A multi-core processor has two or more cores on a
single chip. Two most common multi-core
processors are
– Dual-core Processor: two separate cores on a single chip
– Quad-core Processor: four separate cores on a single chip

• CPU consists of two main units
– Arithmetic and Logic Unit (ALU)
– Control Unit
• These components work together to perform
processing operations.

• ALU is the part of CPU where actual execution
of instructions takes place.
• All arithmetic and logical operations are
performed in ALU.
• ALU consists of two units
– Arithmetic Unit
– Logic Unit

• Arithmetic unit of ALU performs basic
arithmetic functions such as addition,
subtraction, multiplication and division.
• Logic Unit of ALU performs logical operations
like comparing two data items to find which
data item is greater to, equal to or less than
the other.

• Control unit is the component of CPU that acts
like a supervisor of the computer.
• It controls and coordinates all activities of a
computer system by issuing necessary
commands to different components of
computer.

• Important operations performed by control
unit are
– It fetches instructions from the main memory.
– It interprets the instructions to find what
operation is to be performed.
– It controls the execution of instructions.

CPU: Machine Cycle
• CPU uses the machine cycle to process each
instruction. Four steps of machine cycle are
– Fetch: Instruction fetch is a process of getting an
instruction from the memory to execute it. It is
performed by the control unit.
– Decode: The control unit decodes the instruction.
This process examines the nature of instruction to
determine what further operations should be
taken. CU directs to move the required data from
memory to ALU.

CPU: Machine Cycle
– Execute: After decoding the instruction and
getting the required data, CPU finally executes
that instruction. The instructions are executed by
ALU.
– Storing: the process of writing the result to the
memory is called storing.
• These four operations collectively called a
machine cycle or instruction cycle.

CPU: Instruction Set
• A set of all instructions that can be performed by a CPU is
called instruction set. The instruction set consists of four
types of instructions
– Arithmetic Instruction: The instructions used to perform
arithmetic operations are called arithmetic instructions. Different
arithmetic operations are addition, subtraction, multiplication
and division.
– Logical Instruction: The instructions used to perform logical
operations are called logical instructions. A logical operations is
the comparison of two data values e.g. greater than, equal to and
less than.
• Both these instructions are executed by ALU.

CPU: Instruction Set
– Data Transfer Instruction: The instructions used to
transfer data from one component to another
component are called data transfer instructions.
– Control Transfer Instruction: The instructions used
to change the execution sequence of instructions
of a program are called control transfer
instructions. These instructions transfer the
execution control to a certain part of program
instead of next instruction.
• These instructions are executed by CU.

CPU: System Clock
• The processor relies on a small quartz crystal circuit called the
system clock to control the timing of all computer operations.
• Just as your heart beats at a regular rate to keep your body
functioning, the system clock generates regular electronic
pulses, or ticks, that set the operating pace of components of
the system unit.
• Each tick equates to a clock cycle.
• In the past, processors used one or more clock cycles to
execute each instruction.
• Processors today often are superscalar, which means they can
execute more than one instruction per clock cycle.

CPU: System Clock
• The pace of the system clock, called the clock speed, is
measured by the number of ticks per second.
• Current personal computer processors have clock speeds in
the gigahertz range. Giga is a prefix that stands for billion, and
a hertz is one cycle per second.
• Thus, one gigahertz (GHz) equals one billion ticks of the
system clock per second.
• A computer that operates at 3 GHz has 3 billion (Giga) clock
cycles in one second (hertz).
• The faster the clock speed, the more instructions the
processor can execute per second.

CPU: Registers
• A processor contains small, high-speed
storage locations, called registers, which
temporarily hold data and instructions.
• Registers are part of the processor, not part of
memory or a permanent storage device.
• Processors have many different types of
registers, each with a specific storage function.

CPU: Registers
• Register functions include
– storing the location from where an instruction was
fetched
– storing an instruction while the control unit
decodes it
– storing data while the ALU computes it
– storing the results of a calculation.

CPU: Registers
• Some registers are
– Instruction register is used to store the fetched instruction.
– Address Register is used to store the memory address of
data being used by the CPU.
– Storage register store data retrieved from main memory
prior to processing.
– Accumulative Register store the results of arithmetic &
logic operations
– Program Counter is used to store the address of next
instruction to be fetched for execution.

CPU: Pipelining
• Pipelining is a technique in which CPU fetches
the next instruction before it completes the
machine cycle for the first instruction.
• Modern computers use pipelining to process
multiple instructions at the same time.
• It results in the faster processing and increases
the performance of computer.

CPU: Pipelining
• Without pipelining, the processor fetches,
decodes, executes and stores only one
instruction at a time.
• CPU waits until an instruction completes its all
four stages and then executes the next
instruction.

CPU: Processor Cooling
• Proper cooling for processor is very important
as excessive heat can cause problems or even
damage a processor.
• The computer provides cooling system for the
processor.
• Heat sink, cooling fans and liquid cooling
system are used to keep safe the processor
from overheating.

Memory
• A memory is just like a human brain.
• It is used to store data and instructions.
• Computer memory is the storage space in the
computer, where data ( that is to be
processed) and instructions (required for
processing) are stored.

Memory
• Memory consists of millions of cells of storage
locations.
• Each cell can store a bit.
• Bit stands for binary digit..
• One bit can represent 0 or 1.
• The memory cells are logically organized into
groups of 8 bits known as byte.

Memory
• Each byte in the memory has a unique number
assigned to it.
• This number is known as the address of that byte.
• The main memory can be viewed as a collection
of bytes arranged in an order.
• CPU can access any byte from main memory.
• A particular byte in the memory can be accessed
by specifying its address.

Memory
• There are two types of memory
• Volatile memory: it looses its contents when
the computer is turned off. RAM is the most
common type.
• Non-volatile memory: it does not lose its
contents when the computer is turned off.
ROM, flash memory and CMOS are examples.

Memory: RAM
• RAM stands for random access memory, it is a
volatile memory and is also called primary or
main memory.
• Random access means that each individual byte
in entire memory can be accessed directly.
• RAM is used to store data and instructions
temporarily.
• A program must be loaded into RAM before
execution.

Memory: RAM
• RAM plays very important role in the
processing speed of a computer.
• A bigger RAM size provides larger amount of
space for processing, thus increasing
processing speed.
• Types of RAM are
– DRAM
– SRAM

Memory: RAM
• DRAM stands for dynamic random access memory.
• It is used in most computers and is least expensive kind
of RAM.
• It requires an electric current to maintain its electrical
state.
• The electrical charge of DRAM decreases with time that
may result in loss of data, therefore it is recharged again
and again to maintain its data.
• Processor cannot access the data of DRAM when it is
being refreshed, that’s why it is slow.

Memory: RAM
• SRAM stands for static random access
memory.
• It can store data without any need of frequent
recharging.
• CPU doesn’t need to wait to access data,
that’s why it is faster than DRAM.
• It utilizes less power than DRAM but is more
expensive.

Memory: ROM
• ROM stands for read-only memory, and the name stems
from the fact that while data can be read from this type of
computer memory, data cannot normally be written to it.
• It is a very fast type of computer memory which is usually
installed close to the CPU on the motherboard.
• ROM is a type of non-volatile memory, which means that
the data stored in ROM persists in the memory even
when it receives no power – for example when the
computer is turned off.

Memory: ROM
• When a computer is turned on, the CPU begin reading
information stored in ROM.
• When a computer is switched on, the instructions in the
ROM are automatically loaded into the main memory.
• The ROM usually contains "bootstrap code" which is
the basic set of instructions a computer needs to carry
out to become aware of the operating system stored in
secondary memory, and to load parts of the operating
system into primary memory so that it can start up and
become ready to use.

Memory: ROM
• Different types of ROM are
– PROM
– EPROM
– EEPROM

Memory: ROM
• PROM stands for programmable read only
memory.
• It is initially blank and user or manufacturer
can write data and programs on it.
• The user can write data only once, if there is
an error it can not be removed and chip
becomes unusable.

Memory: ROM
• EPROM stands for Erasable Programmable
Read Only Memory.
• It is initially blank and user or manufacturer
can write data and programs on it.
• The data written on it can be erased with
special devices using ultraviolet rays.

Memory: ROM
• EEPROM stands for Electronically Erasable
Programmable Read Only Memory.
• Here, user can erase or write data with the
help of electrical pulses.
• The contents of EEPROM can be easily
modified.

Memory: Cache Memory
• A cache is a small and very fast memory, that
is designed to speed up the transfer of data
and instructions.
• It is located inside or close to the CPU chip and
is faster then RAM.
• The data and instructions that are most
recently and frequently used by CPU are
stored in cache.

• The data and instructions are retrieved from
main memory when CPU uses them for the first
time.
• A copy of that data is stored in cache.
• Next time, when CPU needs that data, it first
looks in cache.
• If the required data is found there, it is retrieved
from cache memory instead of main memory,
thus speeding up the working of CPU.

• A computer can have several different levels of
cache. Different levels of cache memory are
illustrated by figure.

LECTURE NO.03.pptx babsbsbsbsbsbsbsbsbsbbsbs

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