Week 5- computer Hardware

Week-5Week-5The System Unit

Memory Types of Memory

RAM DRAM SRAM

ROM Cache Memory Flash Memory Expansion Slots, cards, Port and Buses Input Devices

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Memory The electronic component which provides storage capability to a

computer is called Memory. Memory contains one or more sets of

chips that store data/program instructions need processing, either temporarily or permanently.

All the computers which are used today needs memory or storage capability.

The CPU accesses each location in memory by using a unique number, called the memory address.

Each byte stored in unique location called an address, similar to addresses on a passenger train

Seat #2B4 Seat #2B3

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Memory Memory (Cont’d)(Cont’d)

The are two types of Memory Random Access Memory Read Only Memory

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Random Access MemoryRandom Access Memory RAM is also called volatile memory and Keeps the information for

a shorter period of time because RAM Lost information if powered off or the computer is shutdown.

RAM store data or instructions, the computer then uses these instructions to perform any processing work.

The contents of RAM change rapidly and often. Typical ranges from Mega Bytes to Giga Bytes Random Access means direct access to any part of memory

The more RAM a The more RAM a computer has, the computer has, the faster it respondsfaster it responds

Also called Also called main memorymain memory

or or primary primary storagestorage

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

power is power is turned offturned off

Memory chips that can be Memory chips that can be read from and written read from and written

to by processorto by processor

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How do program instructions transfer in and out of RAM?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 Operating system instructionsinstructions

Operating system Operating system interfaceinterface

RAM

RAM

Web browser program Web browser program instructions are instructions are

removed from RAMremoved from RAM

Web browser Web browser window no longer is window no longer is displayed on desktopdisplayed on desktop

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.

Step 3. When you quit a program, such as the Web browser, its program instructions are removed from RAM. The Web browser no longer is displayed on the screen.

Word processing Word processing program instructionsprogram instructions

Word processing Word processing program windowprogram window

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Where does Memory Reside?Where does Memory Reside?

Resides on small Resides on small circuit board called circuit board called memory modulememory module

Memory slotsMemory slots on on motherboard hold motherboard hold memory modulesmemory modules

memory chip memory slot

dual inline memory module

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Random Access Memory Random Access Memory (Cont’d)(Cont’d)

The amount of RAM in a PC has a direct affect on the system's speed.

The more RAM a PC has, the more program instructions and data can be held in memory, which is faster than storage on disk.

More RAM = Better Performance !

There are two types of RAM Dynamic RAM Static RAM

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Random Access Memory Random Access Memory (Cont’d)(Cont’d)

Dynamic RAM Dynamic RAM (DRAM) chips must be recharged with

electricity very frequently, or they will lose their contents. DRAM is further divided in two types

SDRAM DDR-SDRAM

It achieves twice the bandwidth of the preceding single data rate SDRAM

Static RAM Static RAM (SRAM) does not need to be recharged as often as

DRAM, and can hold its contents longer.

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Read Only MemoryRead Only Memory ROM is non-volatile memory. The kind of memory is generally programmed by manufacturer. It contains information that is permanently stored. The contents

of ROM are set during manufacturing process. Most of the ROMs are special purpose memories.

Example of ROM is BIOS (Basic Input Output System).

TYPES OF ROM

PROM (Programmable Read Only Memory) Normally ROM’s are not writable but PROM’s are writable. Data can

be written to PROM’s using special devices. Data once written cannot be removed. Ultraviolet Rays are used to

write data in PROM’s.

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Read Only Memory (Cont’d)Read Only Memory (Cont’d)

EPROM (Erasable Programmable Read Only Memory) The only difference between PROM and EPOROM is that data

once written to PROM cannot be removed but EPROM allows to erase the data as well. Ultra Volatile Rays are used to write and erase data from EPROM's.

EEPROM (Electronically Erasable Programmable Read Only Memory)

EEPROM needs an electric impulse to write or erase data. It has all the features of EPROM except the difference of

erasing technique i.e. it uses electric impulse instead of ultraviolet light rays for erasing.

Therefore erasing can be achieved through the use of keyboard commands without removing the chip physically from the computer.

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Cache MemoryCache Memory Cache memory is high-speed memory that holds the most recent

data and instructions that have been loaded by the CPU. Cache is located directly on the CPU or between the CPU and RAM,

making it faster than normal RAM. CPU-resident cache is called Level-1 (L1) cache. L1 cache usually has a very small capacity, ranging from 8 KB

to 128 KB. The most common size is 128 KB. External cache is called Level-2 (L2) cache.

L2 cache is slower then L1 cache but has much larger capacity, ranging from 64 KB to 4 MB.

The amount of cache memory has a tremendous impact on the computer's speed.

When the processor needs an instruction or data, it searches memory in this order, L1 cache, then L2 cache, then RAM.

If the instructions or data is not found in memory then it must search a slower speed storage medium such as a hard disk, compact disc etc.

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Flash MemoryFlash Memory Nonvolatile memory that can be erased electronically and

reprogrammed Used with PDAs, digital cameras, digital cellular phones,

music players and digital voice recorders.

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Access TimeAccess Time Amount of time it takes processor

to read data from memory Measured in nanoseconds (ns),

one billionth of a second It takes 1/10 of a second to blink

your eye; a computer can perform up to 10 million operations in same amount of time

Term Speed

Millisecond One-thousandth of a second

Microsecond One-millionth of a second

Nanosecond One-billionth of a second

Picosecond One-trillionth of a second

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Expansion Slots and Expansion CardsExpansion 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

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Expansion Slots and Expansion CardsExpansion 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

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Expansion Slots and Expansion CardsExpansion Slots and Expansion Cards Video Adapter Video Adapter The electronic components that generate the signal that is sent

through a cable to a video display. It is usually located on the computer's main system board or on

an expansion board, but it is sometimes builtin. e.g VGA

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Expansion Slots and Expansion Cards What are PC cards and flash memory cards?

A PC card adds memory, sound, modem, and other capabilities to notebook computers

A flash memory card allows users to transfer data from mobile devices to desktop computers

Hot plugging allows you to insert and remove cards while computer is running

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PortsPorts Port connects external devices to system unit

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Ports Ports (Cont’d)(Cont’d)

What is a serial port?

Transmits one bit of data at a time

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

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PortsPorts What is a parallel port?

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

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BusesBuses Channel that allows devices inside

computer to communicate with each other

System bus connects processor and RAM

Bus width determines number of bits transmitted at one time

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Buses (Cont’d)

What is an expansion bus? Allows processor to communicate with peripherals

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Mobile ComputersMobile Computers What is a mobile computer?

PDA

flash memory card

notebook computer

PC Cards in PC Card slots

disk in floppy disk drive battery

CD or DVD drive

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Input DevicesInput Devices Input is any data or instruction entered into the memory of a computer. People have a variety of options available to input data, and instructions

into a computer. Such as, user can type character on a keyboard, click a button or roll a wheel on a mouse, press a finger on a touch screen, speak into a microphone, send images from a digital camera or scan image.

Input Devices An input device is any hardware component that allow user to enter data or

instruction into a computers.

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The KeyboardThe Keyboard The most commonly used input device is the keyboard on which data is

entered by manually keying in or typing certain keys. A keyboard typically has 101 or 105 keys, and often attach via a cable to a serial port, or USB port on the system unit.

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The MouseThe Mouse It is a pointing device which is used to control the movement of a

mouse pointer on the screen to make selections from the screen. A mouse has one to five buttons. The bottom of the mouse is flat

and contains a mechanism that detects movement of the mouse.

Wheel mouse – Contains a rotating wheel used to scroll vertically within a text document; connects to PS/2 port or USB port

Cordless mouse – Uses infrared signals to connect to the computer’s IrDA port; it must be within sight of the receiving port

Wheel Mouse

Cordless Mouse

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The Mouse (Cont’d)The Mouse (Cont’d) Mouse buttons enable the user to initiate actions.

Clicking (left-, right-, or double-clicking) allows the user to select an item on the screen or open a program or dialog box

Click and Drag – Holding down the left mouse button and moving the mouse enables the user to move objects on the screen

An optical mouse has no moving mechanical parts inside. Optical mouse uses devices that emit and sense light to detect

the mouse movement. Some uses optical sensor, other uses a laser. An optical mouse that uses a laser usually requires a special

mouse pad.

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Touchpad & Pointing StickTouchpad & Pointing Stick Touchpad

A touchpad is a small, flat, rectangular pointing device that is sensitive to pressure and motion. To move the pointer using a touchpad, slide the finger tip across the surface of the pad.

Some touchpad have one or more buttons around the edges of the pad, that work like mouse buttons.

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Pointing StickPointing Stick Pointing Stick

A pointing stick is a pressure sensitive pointing device shaped like a pencil eraser that is positioned b/w keys on a keyboard.

To move the pointer using s pointing stick, we push the pointing stick with a finger.

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JoystickJoystick User run game software or flight & driving simulation software often use

a joystick as a pointing device.

A joy stick is a vertical lever mounted on a base. We move the lever on different directions to control the action of the simulated vehicle or player.

The lever usually includes buttons called Triggers that we press to active certain events.

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TrackballTrackball A trackball is a pointing device consisting of a ball held by a socket

containing sensors to detect a rotation of the ball.

The user rolls the ball with the thumb, fingers, or the palm of the hand to move a cursor.