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May 3, 2023 1
Computer Peripherals
Presented By :
Tawhidur Rahman,Lecturer,CSE & ITE,DIU
May 3, 2023 2
Contents This lecture will discuss:
storage devices input devices and output devices.
May 3, 2023 3
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.
May 3, 2023 4
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.
May 3, 2023 5
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.
May 3, 2023 6
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.
May 3, 2023 7
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
May 3, 2023 8
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.
May 3, 2023 9
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.
May 3, 2023 10
USB flash drives The internal components of a typical
flash drive1 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
May 3, 2023 11
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.
May 3, 2023 12
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.
May 3, 2023 13
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
May 3, 2023 14
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.
May 3, 2023 15
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.
May 3, 2023 16
Hard Disk Layout
May 3, 2023 17
Disk Data Layout
May 3, 2023 18
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
May 3, 2023 19
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.
May 3, 2023 20
Finding Sectors Must be able to identify start of track and
sector Format disk
Additional information not available to user Marks tracks and sectors
May 3, 2023 21
Winchester Disk FormatSeagate ST506
May 3, 2023 22
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)
May 3, 2023 23
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
May 3, 2023 24
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
May 3, 2023 25
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)
May 3, 2023 26
Multiple Platters
May 3, 2023 27
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.
May 3, 2023 28
May 3, 2023 29
Floppy Disk 8”, 5.25”, 3.5” Small capacity
Up to 1.44Mbyte (2.88M never popular) Slow Universal Cheap Obsolete?
May 3, 2023 30
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.
May 3, 2023 31
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.
May 3, 2023 32
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
May 3, 2023 33
Winchester Hard Disk Universal Cheap Fastest external storage Getting larger all the time
250 Gigabyte now easily available
May 3, 2023 34
Winchester Hard Disk
May 3, 2023 35
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*
21
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
May 3, 2023 36
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
May 3, 2023 37
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.
May 3, 2023 38
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.
May 3, 2023 39
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
May 3, 2023 40
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).
May 3, 2023 41
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
May 3, 2023 42
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.
May 3, 2023 43
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.
May 3, 2023 44
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
May 3, 2023 45
RAID 0, 1, 2
May 3, 2023 46
Data Mapping For RAID 0
May 3, 2023 47
Magnetic Tape Serial access Slow Very cheap Backup and archive
May 3, 2023 48
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.
May 3, 2023 49
TAPE CARTRIDGE
May 3, 2023 50
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.
May 3, 2023 51
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.
May 3, 2023 52
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.
May 3, 2023 53
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.
May 3, 2023 54
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.
May 3, 2023 55
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.
May 3, 2023 56
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.
May 3, 2023 57
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.
May 3, 2023 58
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.
May 3, 2023 59
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.
May 3, 2023 60
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.
May 3, 2023 61
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.
May 3, 2023 62
Important factors for LCD viewing angle. color support brightness and contrast ratio, aspect ratio,
and input ports (e.g. DVI or VGA).
May 3, 2023 63
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.
May 3, 2023 64
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.
May 3, 2023 65
COMPUTER DISPLAY STANDARD Video
standardDescription
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.
May 3, 2023 66
COMPUTER DISPLAY STANDARD Video
standardDescription
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.
May 3, 2023 67
Computer Display Standard Video
standardDescription
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.
May 3, 2023 68
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.
May 3, 2023 69
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.
May 3, 2023 70
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.
May 3, 2023 71
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
May 3, 2023 72
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.
May 3, 2023 73
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. .
May 3, 2023 74
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.
May 3, 2023 75
Image, video and audio input devices
Image scanner 3D scanner Digital camera Webcam Digital video recorder Digital camcoder Digital audio recorder microphone
May 3, 2023 76
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.
May 3, 2023 77
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.
May 3, 2023 78
Thank you