System unit & its components

04/13/2023 Designed by Prof. Anosha Khan PGC 1

System Unit and its Components

Lecture # 3


System Unit

It contains electronic components of the computers used to process data

system unit

system unit

system unit

system unit


Components of SU

Processor Memory Adapter cards

Sound card Modem card

Ports Drive bays Power supply

power supply

ports

drive bays

processor

memory

sound card

video cardmodem cardnetwork card


(Cont.)


Motherboard

Circuit board:

thin board containing chips—very small pieces of silicon or other semi-conducting material onto which integrated circuits are embedded—and other electronic components

Mother Board Main circuit board in system unit Contains adapter cards, processor chips, and

memory chips Connects all components Allows communication between devices Also called system board


Motherboard

processor chip adapter cards

memory chips

memory slots

motherboard

Expansionslots for adapter cards


What is a chip?

Small piece of semi-conducting material on which integrated circuits are etched Integrated circuits contain

many microscopic pathways capable of carrying electrical current


Central Processing Unit

Interprets and carries out basic instructions that operate a computer

Also called the processor

Processor

Control Unit

Arithmetic Logic Unit (ALU)

Arithmetic Logic Unit (ALU)

InputDevices

StorageDevices

OutputDevicesMemoryData Information

Information

DataInformatio

n

Information

DataInformatio

n

Control Unit


Two Main components of CPU

Arithmetic/Logic Unit (ALU) Perform two types of operations Arithmetic (+,-,*,/) and logic(<,>,=)

Control Unit Tell the rest of the computer how to carry out a program’s

instructions Works with a “program counter” (address of next instruction) It directs the movement of electronic signals between memory,

instructions and arithmetic logic unit. Direct control signals between the CPU and I/O devices.


Machine cycle

There are four operations of Machine CycleStep 1. Fetch

Obtain program instruction or data item from memory

Step 2. Decode Translate instruction into commands

Step 3. Execute Carry out command

Step 4. Store Write result to memory


Pipelining

CPU begins fetching second instruction before completing machine cycle for first instruction

Results in faster processing


System Clock

Important measurement indicating speed Located on a small chip Produces electrical beats(impulse)

Expressed in gigahertz (1 GH=1 billion ticks of system clock per second)

Faster clock speed, faster computer the clock speed determines how many

instructions per second the processor can execute

Processor speed can also be measured in millions of instructions per second (MIPS)

http://www.webopedia.com/TERM/M/processor.html

http://www.webopedia.com/TERM/M/execute.html


Factors affecting CPU performance

Registers Page # 145, topic: Registers Cache System Clock RAM


Heat Sink and Heat Pipe

Heat sink—component with fins that cools processor

Heat pipe—smaller device for notebook computer

heat sink fan


Parallel Processing

Using multiple processors simultaneously to execute a program faster

Requires special software to divide problem and bring results together

Control Processor

Processor 1

Memory

Processor 2

Memory

Processor 3

Memory

Processor 4

Memory

Results combined


Data Representation

Most Computers are digital Recognize only two discrete states: on or off Use a binary system to recognize two states Use Number system

with two unique digits: 0 and 1, called bits (short for binary digits)


Byte

Eight bits grouped together as a unit Provides enough different combinations of 0s and

1s to represent 256 individual characters Numbers Uppercase

and lowercase letters

Punctuation marks


Encoding Schemes

Three types of schemes ASCII - American Standard Code for

Information interchange EBCDIC - Extended Binary Coded

Decimal Interchange Code( used for large computers)

Unicode ( for international languages like Chinese and Japanese.

ASCII Symbol EBCDIC

00110000 0 1111000000110001 1 1111000100110010 2 1111001000110011 3 11110011


Data Representation How is a letter converted to binary form and back?

Step 1.The user presses the capital letter D (shift+D key) on the keyboard.

Step 2.An electronic signal for the capital letter D is sent to the system unit.

Step 3.The signal for the capital letter D is converted to its ASCII binary code (01000100) and is stored in memory for processing.

Step 4.After processing, the binary code for the capital letter D is converted to an image, and displayed on the output device.


Memory

Electronic components that store instructions, data, and results Consists of one or more chips on motherboard or

other circuit board Before running a Program must be loaded into the memory Memory slots on motherboard hold memory modules RAM (random access memory): temporary memory that the

computer uses Consists of chips connected to a memory module which is connected

to the motherboard Hold data and program instructions while they are needed. RAM is volatile, its content is lost

when the computer is shut off


RAM (Random access Memory)

Home Task Explore SRAM, DRAM, SIMM, DIMM

and RIMMVirtual

Memory Small portion

of hard Disk acts as RAM

The more RAM a computer has, the faster it responds

Also called main memory

or primary storage

Most RAM is volatile, it is lost when computer’s

power is turned off

Memory chips that can be read from and written

to by processor


Memory

Types of Memory Volatile , non volatile How is memory measured? By number of bytes available for storage

Term Abbreviation Approximate Size

Kilobyte KB or K 1 thousand bytesMegabyte MB 1 million bytesGigabyte GB 1 billion bytesTerabyte TB 1 trillion bytes


How do program instructions transfer in and out of RAM?

Step 1. When you start the computer, certain operating system files load into RAM from the hard disk. The operating system displays the user interface on the screen.

Operating system instructions

Operating system interface

RAM

Word processing program instructions

Word processing program window

Step 2. When you start a word processing program, the program’s instructions load into RAM from the hard disk. The word processing program, along with the Web Browser and certain operating system instructions are in RAM. The word processing program window is displayed on the screen.


Cache

It helps to increase speed of computer It stores frequently used data and instructions Two types of cache Memory Cache and Disk Cache Memory Cache

L1: built directly in processor, less memory L2:slower but has larger capacity ATC (advanced transfer cache) is a type of L2 cache L3:it is on motherboard separate from processor


Registers

A register is a single storage location within the CPU Unlike memory, which is “outside” the CPU Examples of registers:

Accumulator (ACC) Program counter (PC) Instruction register (IR) Memory address register (MAR) Memory data register (MDR) Status register

General purpose registers (R0, R1, …) Included on some CPUs Used for high-speed temporary storage of program

variables


ROM(Read Only Memory)

Memory chips that store permanent data and instructions

Nonvolatile memory, it is not lost when computer’s power is turned off

PROM (programmable ROM) EEPROM (Electrically erasable read-only memory)


Flash Memory

Nonvolatile memory that can be erased electronically and reprogrammed

Used with PDAs, digital cameras, digital cellular phones, music players, digital voice recorders, and pagers


CMOS

CMOS stands for Complementary metal-oxide semiconductor memory

It is used to store configuration information about the computer

Uses battery power to retain information when other power is turned off

Stores date, time, and computer’s startup information


Expansion Slots and Expansion Cards

What is an adapter card?

Enhances system unit or provides connections to external devices called peripherals

Also called an expansion card Flash Memory Cards PC Cards


Expansion Slots and Expansion Cards What is an expansion slot? An opening, or socket,

on the motherboard that can hold an adapter card

With Plug and Play, the computer automatically configures cardsand other devices as you install them


Ports and Connectors

Port connects external devices to system unit

Connector joins cable to peripheral Available in one

of two genders: male and female


Serial Port

Transmits one bit of data at a time

Connects slow-speed devices, such as mouse, keyboard, modem


Parallel Port

Connects devices that can transfer more than one bit at a time, such as a printer


Bus

Connect parts of the CPU to each other Connect the CPU to other devices on the system board. Data roadway for traveling bits

Measured as bus width( number of bits transmitted at one time) More lanes, faster traffic

Two basic categories of Expansion BUSES System buses ( connect CPU to Memory) Expansion buses ( connect CPU to slots on the system board) Data Bus (Page # 148) Address Bus__Connects only CPU & RAM(Page # 148) BUS standard (chapter 4 page 148)

System unit & its components

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