Lecturer : Dr. Masri Ayob

TK 6123COMPUTER ORGANISATION &

ARCHITECTURE

Lecture 10: Computer Peripheral

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Contents

This lecture will discuss: storage devices input devices and output devices.

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Introduction

The peripherals are referred to all the items that are external to the CPU, main memory and power supply. These includes:

Thumb drive, a floppy disk drive, a hard disk drive, serial ports, parallel port(s), USB ports, a keyboard, a mouse, a network interface, CD-ROM or DVD-ROM drive, a sound system, a modem, a monitor, tape drives, scanners, printers, plotters, and audio, video input devices, etc.

Some of the peripherals use the parallel, USB, and serial ports as their interconnection point to the computer.

Others have their own interface to the system bus.

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Introduction Peripheral devices are classified as

storage devices (secondary memory) Flash memory Magnetic Disk Magnetic tape CD-ROM : (your assignment) Etc.

input devices Keyboard Mouse Touch screen Graphics tablets Etc.

output devices Printers : (your assignment) Scanners Displays Etc.

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Secondary/External Memory

Is treated as I/O. Data and programs in secondary storage must be

copied to primary memory for CPU access. Except for flash memory, secondary storage is

significantly slower than primary storage, and flash memory is expensive compared to other forms of secondary storage.

Most secondary storage devices are mechanical in nature, and mechanical devices are usually slower than devices that are purely electronic.

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Secondary/External Memory

Advantages of secondary storage, Its permanence

The magnetic media used for disk and tape and the optical media used for disk retain the data indefinitely.

Capable of storing massive amounts of data. Used for offline archiving, for transferring programs

and data from machine to machine, installation purposes, and for offsite backup storage.

Relatively inexpensive compared to main memory.

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Types of Secondary Memory

Flash memory Thumb drive

Magnetic Disk RAID Removable

Optical CD-ROM CD-Recordable (CD-R) CD-R/W DVD

Magnetic Tape

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USB flash drives

Typically small, lightweight, removable and rewritable.

Memory capacity typically ranges from 8 MB up to 64 GB, limited only by current flash memory densities. As capacity increases, so does price.

Several advantages over other portable storage devices: Generally faster, hold more data, and are considered

more reliable (due to their lack of moving parts) than floppy disks.

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USB flash drives

A flash drive has a small PCB encased in a robust plastic or metal casing, making the drive sturdy enough to be carried about in a pocket. Only the USB connector protrudes from this protection,

and is usually covered by a removable cap. Most flash drives use a standard type-A USB connection

allowing them to be connected directly to a port on a personal computer.

Most flash drives are active only when powered by a USB computer connection, and require no other external power source or battery power source.

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USB flash drives The internal components of a typical

flash drive

1 USB connector

2 USB mass storage controller device

3 Test points

4 Flash memory chip

5 Crystal oscillator

6 LED

7 Write-protect switch

8 Unpopulated space for second flash memory chip

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USB flash drives

The controller contains a small RISC microprocessor and a small amount of on-chip ROM and RAM.

Flash storage devices are best compared to other common, portable, swappable data storage devices: floppy disks, Zip disks, and CD-R/CD-RW discs. 3.5 inch floppy disks and Iomega Zip disks.

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USB flash drives

An obvious extension of flash memory would be as a replacement for hard disks. Flash memory does not have the mechanical

limitations and latencies of hard drives. is attractive when considering speed, noise,

power consumption, and reliability However, the cost per gigabyte of flash

memory remains significantly higher than that of platter-based hard drives.

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Magnetic Disk

A magnetic disk consists of one or more flat, circular platters made of glass, metal, or plastic, and coated with a magnetic substance similar to that used on cassette tape.

Substance used to be aluminium Now glass

Improved surface uniformity Increases reliability

Reduction in surface defects Reduced read/write errors

Better shock/damage resistance

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Magnetic Disk

There are two major types of magnetic disks, hard disks and floppy disks or diskettes.

The design of a floppy disk limits the number of surfaces to two, specifically the top and bottom of the single disk platter within its diskette case.

Most hard disk drives contain several platters, all mounted on the same axis, with heads on each surface of each platter.

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Magnetic Disk

The heads move in tandem, so they are positioned over the same point on each surface.

With the head in a particular position, it traces out a circle (track) on the disk surface as the disk rotates;

Since the heads on each surface all line up, the set of tracks for all the surfaces form a cylinder.

Each track contains one or more blocks of data, which commonly divided into equally sized pie shape segments (sectors).

Each sector on a single track contains one block of data, typically 512 bytes, and represents the smallest unit that can be independently read or written.

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Hard Disk Layout

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Disk Data Layout

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Disk Velocity

Bit near centre of rotating disk passes fixed point slower than bit on outside of disk

Increase spacing between bits in different tracks Rotate disk at constant angular velocity (CAV)

Gives pie shaped sectors and concentric tracks Individual tracks and sectors addressable Move head to given track and wait for given sector Waste of space on outer tracks

Lower data density Can use zones to increase capacity

Each zone has fixed bits per track More complex circuitry

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Disk Layout Methods Diagram

Multiple zone recording - A few high-density disks are designed with a different number of sectors in different tracks. This technique uses a constant speed motor but compensates for different transfer speeds in the controller.

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Finding Sectors

Must be able to identify start of track and sector

Format disk Additional information not available to user Marks tracks and sectors

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Winchester Disk FormatSeagate ST506

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Characteristics

Fixed (rare) or movable head Removable or fixed Single or double (usually) sided Single or multiple platter Head mechanism

Contact (Floppy) Fixed gap Flying (Winchester)

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Fixed/Movable Head Disk

Fixed head One read write head per track Heads mounted on fixed ridged arm

Movable head One read write head per side Mounted on a movable arm

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Removable or Not

Removable disk Can be removed from drive and replaced with

another disk Provides unlimited storage capacity Easy data transfer between systems

Nonremovable disk Permanently mounted in the drive

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Multiple Platter

One head per side Heads are joined and aligned Aligned tracks on each platter form cylinders Data is striped by cylinder

reduces head movement Increases speed (transfer rate)

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Multiple Platters

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Tracks and Cylinders

Hard Disk

Hard disk drives are accessed over one of a number of bus types: Parallel ATA (PATA, also called IDE or EIDE), Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel.

Bridge circuitry is sometimes used to connect hard disk drives to buses that they cannot communicate with natively, such as IEEE 1394 and USB.

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Floppy Disk

8”, 5.25”, 3.5” Small capacity

Up to 1.44Mbyte (2.88M never popular) Slow Universal Cheap Obsolete?

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Floppy disks vs hard disks A little difference between the operation of floppy

disks and hard disks, but the mechanical differences have important effects on the overall capacity, speed, data transfer rate, and reliability of hard drives versus floppy disks. Capacity: hard disk > a floppy disk The heads on a hard disk do not touch the surface; rather,

they ride on a bed of air a few millionths of an inch above the surface - allows the disk to rotate at high speed and also allows the designers to locate the tracks very close together. The result is a disk that can store large amounts of data and that retrieves data quickly.

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Floppy disks vs hard disks Because the floppy disk is soft and flexible,

it is necessary to support the disk surface as data is being read and written.

To do so, the disk is pinched lightly between two heads, one on each surface of the disk.

As a result of this physical contact between the disk surface and the heads, the disk must be rotated more slowly, so as not to wear out the heads or scrape the disk surface.

A typical hard disk rotates at 5400 revolutions per minute (rpm), 7200rpm, or even 10,800rpm.

The floppy disk rotates at 360 rpm.

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Winchester Hard Disk

Developed by IBM in Winchester (USA) The entire assembly is sealed to prevent dirt

particles from wedging between the heads and the disk platter.

One or more platters (disks) Heads fly on boundary layer of air as disk

spins Very small head to disk gap Getting more robust

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Winchester Hard Disk

Universal Cheap Fastest external storage Getting larger all the time

250 Gigabyte now easily available

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Winchester Hard Disk

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Speed

Seek time The arm first moves the head from its present track until it is

over the desired track. The average seek time is used as a specification for the disk.

Rotational latency (or rotational delay or latency time) Once the head is located over the desired track, the

read/write operation must wait for the disk rotate to the beginning of the correct sector.

SpeedRotationalencyAverageLat

1*2

1

For a typical hard disk rotating at 3600 revolutions per minute, or 60 revolutions per second, the average latency is: ½ * 1/60 = 8.33msec

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Speed

Access time = Seek + Latency Transfer time – is the time required to transfer

the block. The transfer time is defined by:

SpeedRotationalctorsNumberOfSe *

1Transfer time =

For example, a hard disk rotating at 3600 rpm (or 60 revolutions per second), with 30 sectors per track. The transfer time for a single block would be: 1/(30*60) =0.55 msec

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BERNOULLI DISK DRIVES

Bernoulli disk drives offer a hybrid approach to disk design that embodies the advantages of both floppy disk and hard disk technology.

The disk platter is a 3 1/2” floppy disk housed in a removable plastic shelled cartridge slightly thicker than that of a standard floppy disk.

The floppy disk platter spins at about 3000 rpm. The Bernouffi principle states that a low-pressure

layer is formed next to a surface moving rapidly in a fluid medium such as air.

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BERNOULLI DISK DRIVES

The more rapid the surface is moving, the lower the pressure.

When not operating, the floppy medium bends away from the read/write head.

A cushion of air keeps the head from touching the surface.

Thus, the Bernoulli cartridge has the advantages of a hard disk drive, but with the flexibility of an inexpensive, removable cartridge.

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BERNOULLI DISK DRIVES

Notice that when something goes wrong, the tendency of the Bernoulli disk is to fall away from the head, thus protecting the device from head crashes.

Because of the design, the Bernoulli drive uses only one surface and has only a single head.

Example: Zip drives

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Disk Array

In larger computer environments, that provide program and data storage facilities for a network, it is common to group multiple disks together.

Such a grouping of two or more disk drives is called a disk array or a drive array.

A disk array can be used to reduce overall data access time by sharing the data among multiple disks and also to increase system reliability.

The assumption made is that the number of blocks to be manipulated at a given time is large enough and important enough.

Example: RAID (Redundant array of inexpensive disks).

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RAID

Redundant Array of Inexpensive Disks (defined by Patterson et al., 1988).

Redundant Array of Independent Disks (industry redefined ‘I’ to be ‘Independent’)

7 levels in common use: RAID 0, RAID 1,….RAID 6 Not a hierarchy but designate different design

architecture. Set of physical disks viewed as single logical drive by

O/S Data distributed across physical drives Can use redundant capacity to store parity information

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RAID

Two standard methods of implementing a disk array: mirrored array

Has two or more disk drives. each disk stores exactly the same data. During reads, alternate blocks of the data are read

from different drives, then combined to reassemble the original data – faster access time.

striped array requires a minimum of three disk drives. one disk drive is reserved for error checking. A file segment to be stored is divided into blocks, which

are then written simultaneously to different disks.

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Example: RAID 0

No redundancy Data striped across all disks Round Robin striping Increase speed Use in supercomputer where performance

and capacity are important and low cost is more important than reliability.

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Example: RAID 1

Mirrored Disks Data is striped across disks 2 copies of each stripe on separate disks Read from either Write to both Recovery is simple

Swap faulty disk & re-mirror No down time

Expensive

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RAID 0, 1, 2

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Data Mapping For RAID 0

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Magnetic Tape

Serial access Slow Very cheap Backup and archive

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MAGNETIC TAPE

Is used for secondary storage: when offline storage is acceptable or preferred, when the data storage capacity requirements exceed those

of a floppy disk and when sequential access is adequate.

Tape is nonvolatile, and the data can be stored indefinitely. Modern computers all use tape cartridges for offline storage.

easy to mount and dismount, and small and easy to store. Some can store as much as 300GB of compressed data.

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TAPE CARTRIDGE

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DISPLAYS A computer display (also known as a computer monitor,

computer screen, or computer video display) is a device that can display signals generated by a computer as images on a screen.

It is used to display image (or text) to the user. An image made up of thousands of individual pixels, or

picture elements, arranged to make up a large rectangular screen.

Each pixel is a tiny square on the display. A typical screen/display is made up of 768 rows of 1024

pixels each, known as a 1024 x 768 pixel screen. Screens of 640 x 480 pixels or 800 x 600 pixels are also still

in use, and resolutions of 1280 x 1024 pixels, or even higher have become common, especially on physically larger screens.

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DISPLAYS

The resolution specifies the minimum identifiable pixel size capability of the monitor, therefore, the smaller the number the better.

Each individual pixel represents a shade of gray (on a monochrome screen) or a colour.

A color pixel is actually made up of a mixture of different intensities of red, green, and blue (RGB).

A monochrome scale with no shading would require only 1 bit per pixel (‘1’ for white, ‘0’ for black).

Typical colour display has 256 colours, or many more. It takes 1 byte per pixel to represent a 256-clour image.

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DISPLAYS

True colour system use 8 bit per colour (i.e. 24 bit in all). It can represent 256*256*256 different colours on

the screen. With 8 bits, there is no way to divide the bits

to represent reds, blues, and greens equally. Instead, 256 arbitrary combinations of red, blue,

and green are chosen from a larger palette of colors.

More commonly, a default color scheme is used.

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DISPLAYS

Each pixel value is represented by a value of 0-255, representing the color for that pixel.

A color transformation table, also known as a palette table, holds the RGB values for each of the 256 possible colors.

To display a pixel on the screen, the system transforms the pixel color to a screen color by reading the RGB values that correspond to the particular pixel value from the table - is performed by a special circuitry on the video card.

Most output, including text data, is presented graphically.

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DISPLAYS

In some PCs, the display circuitry is usually provided on a separate plug-in video card; video memory is supplied with the card.

In some PCs, and most laptops, the video circuitry is included on the motherboard.

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DISPLAYS The actual display is produced by scanning and

displaying each pixel, one row at a time, from left to right, then from top to bottom.

Known as a raster scan. Identical to the way that television pictures are generated.

Some monitors Interlace the display, by displaying the odd rows (i.e. row 1, 3, 5 etc.) and then coming back and displaying the even rows.

Not popular - results in flickering that is annoying to some users.

Vector scan - pixels are displayed in whatever order is necessary to trace out a particular image.

E.g. by following the outline of the character vector scan could trace a character.

Not suitable for bit map graphics, but can be used with object graphics images, such as those used for CAD/CAM applications.

Generating vector scan images on a display screen is electronically much more difficult and expensive than producing raster scans

Thus, raster scans are used almost universally today.

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CRT Display Technology LCD has become more common, but

cathode ray tube (CRT) remains the most common display technology.

3 electron guns (red, blue, and green) within the tube shoot beams of electrons from the back of the tube.

There is a high voltage applied to the inside of the face of the tube attracts the beams to the face.

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CRT Display Technology The face of the tube is painted with tiny dots

or thin stripes of phosphors, which glow when struck by electrons.

A shadow mask in the tube is designed such that electrons from each gun can strike only phosphors of the matching color.

The strength of the beams varies depending on the color and brightness of the point being displayed: The stronger the beam for a particular color,

the brighter that color appears on the screen.

Monochrome video monitors work identically, except that only a single gun is required, the phosphor is white, yellow, or green, and no shadow mask is required.

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Issues and Problems with Computer Display

Screen burn-in: an image is displayed on the screen for a long period of time without changing, the screen that is showing will embed itself into the glass. use a good screensaver program that

rotates often. Some LCD monitors may get "dead pixels"

over time. This generally applies to older LCD

monitors from the 1990's.

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Liquid Crystal Display Technology

A liquid crystal display (LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector.

it uses very small amounts of electric power, and is therefore suitable for use in battery-powered electronic devices.

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Important factors for LCD Important factors to consider when evaluating an

LCD monitor include: Resolution:

the physical number of columns and rows of pixels creating the display (eg, 852x480; 1368x768 etc).

viewable size. response time (sync rate) - amount of time a pixel in an

LCD monitor takes to go from active (black) to inactive (white) and back to active (black) again (ms).

Lower numbers mean faster transitions and therefore fewer visible image artifacts.

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Important factors for LCD

matrix type (passive or active): High-resolution color displays such as modern

LCD computer monitors and televisions use an active matrix structure.

Active-matrix displays are much brighter and sharper than passive-matrix displays of the same size, and generally have quicker response times, producing much better images.

Active matrix display: the display panel contains one transistor for each cell in the matrix.

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Important factors for LCD

viewing angle. color support brightness and contrast ratio, aspect ratio,

and input ports (e.g. DVI or VGA).

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LCD DISPLAYS

LCD panels have the advantage of: small size, bright images, no flicker, and low power consumption.

so they are ideal for laptop computers.

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COMPUTER DISPLAY STANDARD

Video standard

Description

MDA Monochrome Display Adapter, the original standard on IBM PCs and IBM PC XTs with 4 KB video RAM. Introduced in 1981 by IBM. Supports text mode only.

CGA Color Graphics Adapter. Introduced in 1981 by IBM, as the first color display standard for the IBM PC. The standard CGA graphics cards were equipped with 16 KB video RAM.

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COMPUTER DISPLAY STANDARD

Video standard

Description

EGA Enhanced Graphics Adapter. Introduced in 1984 by IBM. A resolution of 640 × 350 pixels of 16 different colors (4 bits per pixel, or bpp).

VGA Video Graphics Array, introduced in 1987 by IBM. VGA is actually a set of different resolutions, but is most commonly used today to refer to 640 × 480 pixel displays with 16 colors (4 bits per pixel).

SVGA Super VGA, a video display standard created by VESA for IBM PC compatible personal computers. Introduced in 1989.

XGA Extended Graphics Array is an IBM display standard introduced in 1990. XGA-2 added 1024 × 768 support for high color and higher refresh rates, improved performance, and support for 1360 × 1024 in 16 colors (4 bits per pixel).

The Video Electronics Standards Association (VESA) is an international body, founded by NEC Home Electronics and eight other video display adapter manufacturers.

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COMPUTER DISPLAY STANDARD

Video standard

Description

SXGA Super XGA, a widely used de facto 32 bit Truecolor standard. The resolution: 1280×1024

UXGA Ultra XGA is a de facto Truecolor standard. The resolution: 1600×1200

WUXGA Widescreen Ultra Extended Graphics Array is a version of the UXGA format. This display is becoming popular in high end 15" and 17" widescreen notebook computers. The resolution: 1920X1200.

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Computer Display Standard

Video standard

Description

WQXGA Widescreen Quad Extended Graphics Array is a version of the XGA format. This display is becoming popular in some recent desktop monitors. The resolution: 2560x1600.

WXGA Widescreen Extended Graphics Array is a version of the XGA format. This display is becoming popular in some recent notebook computers. The resolution: 1280x720.

WSXGA, or WXGA+

Widescreen Extended Graphics Array PLUS is a version of the WXGA format. This display aspect ratio is becoming popular in some recent notebook computers. The resolution: 1440x900.

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Scanners

Primary used - to input paper images. A device that analyzes an image or an object (such as

an ornament) and converts it to a digital image. Scanners are generally less expensive and more

convenient. 3 primary types of scanners:

flatbed scanners, sheet-fed scanners, handheld scanners, but all 3 work similarly and differ only in the way the scan

element is moved with respect to the paper.

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Scanners

In a flatbed scanner, the paper is placed on a glass window, while the scan element moves down the page, much like a copy machine.

In a sheet-fed scanner, a single page of paper is propelled through the mechanism with rollers; the scan element is stationary.

Handheld scanners are propelled by the user over the page.

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Scanners

The scanning mechanism consists of a light source and a row of light sensors. As the light is reflected from individual points on

the page, it is received by the light sensors and translated to digital signals that correspond to the brightness of each point.

Color filters can be used to produce color images. The resolution of scanners is approximately

600—2400 points per inch.

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User Input Devices

Users use a variety of devices to interact with the computer: Text Input:

Keyboards (most popular) - consist of a number of switches and a keyboard controller. The keyboard controller is built into the keyboard itself.

Speech recognition. Pointing devices:

Mouse- a handheld pointing device, designed to sit under one hand of the user and to detect movement relative to its two-dimensional supporting surface.

mechanical mouse

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Pointing devices

Optical mouse uses a light-emitting diode and photodiodes to detect the movement of the underlying surface, rather than moving some of its parts as in a mechanical mouse.

Laser mouse uses a small laser instead of a LED.

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USER INPUT DEVICES

Operating a mechanical mouse.1: Moving the mouse turns the ball.2: X and Y rollers grip the ball and transfer movement.3: Optical encoding disks include light holes.4: Infrared LEDs shine through the disks.5: Sensors gather light pulses to convert to X and Y velocities. .

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Pointing devices Joystick Touch screen Touchpad Light pen- pointed at the screen to identify a

position on the screen. By moving the pen around the screen, a cursor can be made to follow the pen.

Graphics tablet.

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Image, video and audio input devices

Image scanner 3D scanner Digital camera Webcam Digital video recorder Digital camcoder Digital audio recorder microphone

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Communication Devices Like other I/O devices, there is a network interface

unit (NIU) that handles the physical characteristics of the connection and one or more I/O drivers that manage and steer input data, output data, and interrupts.

The interface between a computer and a network is more complicated than that for most other I/O peripherals.

Data must be formatted in specific ways to communicate successfully with a wide range of application and system software located on other computers.

The computer also must be able to address a large number of devices individually, specifically, every other computer connected to the network.

Security of communication is important.

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Communication Devices

Most of these concerns are handled with protocol software in the operating system.

The NIU is responsible only for: the electrical signals that connect the computer to the

network, either directly or through a communication channel, and

for the protocols, implemented in hardware, that define the specific rules of communication for the network.

These protocols are called medium access control protocols, or MACs.

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Thank youQ & A