1 Lecture 10 Computer Peripherals ITEC 1000 “Introduction to Information Technology”

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Lecture 10Lecture 10

Computer PeripheralsComputer Peripherals

ITEC 1000 “Introduction to Information Technology”

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Lecture Template:Lecture Template:

PeripheralsPeripherals Storage DevicesStorage Devices DisplaysDisplays PrintersPrinters ScannersScanners Pointing DevicesPointing Devices

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PeripheralsPeripherals

Devices that are external to the main processing function of the computer

Not the CPU, memory, power supply Classified as input, output, and storage Connected via

Ports• parallel, USB, serial

Interface to systems bus • SCSI, IDE, PCMCIA

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Storage Devices: TerminologyStorage Devices: Terminology

Medium• The technology or product type that holds the

data Access time

• The time to locate data and read it• Specified as an average in seconds (e.g., s, ms,

µs, ns, etc.) Throughput/Transfer rate

• Amount of data (in consecutive bytes) moved per second

• Specified in bytes/s (e.g., Kbytes/s, Mbytes/s)

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Storage DevicesStorage Devices

Primary memory (cache, conventional memory) – immediate access by CPU

Expanded storage (e.g., RAM) – a buffer between conventional memory and secondary memory)

Secondary storageData and programs must be copied to primary memory for CPU accessPermanence of dataMechanical devicesDirect access storage devices (DASDs)Online storageOffline storage – loaded when needed

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Storage HierarchyStorage Hierarchy

Offlinestorage

Secondarystorage

Primarystorage

MediumCPU registersCache memoryConventional memoryExpanded memoryHard diskFloppy diskCD-ROMTape

Access Time-15-30 ns50-100 ns75-500 ns10-50 ms95 ms100-600 ms0.5+ s

Throughput----600-6000 Kbytes/s100-200 Kbytes/s150-1000 Kbytes/s5-20 Kbytes/s (cartridge)200-3000 Kbytes/s (reel-to-reel)

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Online storageMemory that is accessible to programs without human interventionPrimary storage and secondary storage are “online”

Primary storageSemiconductor technology (e.g., RAM)Volatile (contents might be lost when powered off )

Secondary storageMagnetic technology (e.g., disk drives)Non-volatile (contents are retained in the absence of power)

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Offline storageMemory that requires human intervention in order for it to be accessed by a program (e.g., loading a tape)Sometimes called “archival storage”

Direct Access Storage Device (DASD)Pronounced “dazz-dee”Term coined by IBMDistinguishes disks (disk head moves “directly” to the data) from tapes (tape reel must wind forward or backward to the data: sequential access)

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Secondary Storage DevicesSecondary Storage Devices

Hard drives, floppy drives CD-ROM and DVD-ROM drives CD-R, CD-RW, DVD-RAM, DVD-RW Tape drives Network drives Direct access vs. Sequential access Rotation vs. Linear

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Magnetic DisksMagnetic Disks

A magnetic substance is coated on a round surface The magnetic substance can be polarized in one of

two directions with an electromagnet (“writing data”)

The electromagnet can also sense the direction of magnetic polarization (“reading data”)

Similar to a read/write head on a tape recorder (except the information is digital rather than analogue)

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Track – circle Cylinder – same track on all platters Block – small arc of a track Sector – pie-shaped part of a platter Head – reads data off the disk Head crash Parked heads Number of bits on each track is the same! Denser

towards the center. CAV – constant angular velocity

Spins the same speed for every trackHard drives – 3600 rpm – 7200 rpmFloppy drives – 360 rpm

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Floppy DisksFloppy Disks

Also called “flexible disks” or “diskettes” The platter is “floppy”, or flexible (e.g.,

mylar) (typical: 5.25”, 3.5”) Most floppy disk drives can hold one

diskette (two surfaces) The diskette is removable Typical rpm: 300, 360 Capacities: 180 KB to 1.4 MB (& up to 100

MB “zip” disks, more)

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Floppy Disk: ExampleFloppy Disk: Example

Writeprotect tab

Spindle

ShutterAccess window

Cutawayshowing disk

Case

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Hard DisksHard Disks

The platter is “hard” (e.g., aluminum) Most hard disk drives contain more than

one platter On most hard disk drives, the disks are

“fixed” (i.e., not removable) On some hard disk drives, the disks are in

a removable pack (hence, “disk pack”) Typical speed of rotation: 3600, 5400,

7200 rpm (rpm = “revolutions per minute”)

Capacities: 5 MB to 1+ TB (terabyte = 240 bytes)

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Hard Disks: ExampleHard Disks: Example

Top view of a 36 GB, 10,000 RPM, IBM SCSI

server hard disk, with its top cover removed, 10 stacked

platters(The IBM Ultrastar 36ZX)

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Winchester DisksWinchester Disks

Invented by IBM A type of hard disk drive The disk is contained within a sealed unit No dust particles When powered off, the head is “parked” at the

outer edge of the platter and rests on the platter surface

When powered on, the aerodynamics of the head and enclosure create a cushion of air between the head and the disk surface

The head floats above the surface (very close!) and does not touch the surface

Thus, “head crash” (the head touches the surface, with damage resulting)

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Winchester Disks: ExampleWinchester Disks: Example

IBM's Winchester disk was a removable cartridge, but the heads and platters were built in a sealed unit and were not separable

http://encyclopedia2.thefreedictionary.com/

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Hard Disk LayoutHard Disk Layout

Platter

Track

Cylinder

Drivemotor

Headmotor

Head, onmoving arm

Block

Sector

Track

Head

Head assembly

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Hard Disk: TerminologyHard Disk: Terminology

Platter• A round surface – the disk – containing a magnetic coating

Track• A circle on the disk surface on which data are contained

Head• A transducer attached to an arm for writing/reading data

to/from the disk surface Head assembly

• A mechanical unit holding the heads and arms• All the head/arm units move together, via the head

assembly Cylinder

• A set of tracks simultaneously accessible from the heads on the head assembly

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Drive motorThe motor that rotates the plattersTypically a DC motor (DC = direct current)The disk rotates at a fixed speed (e.g., 3600 rpm, revolutions per minute)

Head motionA mechanism is required to move the head assembly in/outTwo possibilities:

A stepper motor (digital, head moves in steps, no feedback)A servo motor (analogue, very precision positioning, but requires feedback)

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SectorThat portion of a track falling along a predefined pie-shaped portion of the disk surfaceThe number of bytes stored in a sector is the same, regardless of where the sector is located; thus, the density of bits is greater for sectors near the centre of the diskThe rotational speed is constant; i.e., constant angular velocityThus, the transfer rate is the same for inner sectors and outer sectors

BlockThe smallest unit of data that can be written or read to/from the disk (typically 512 bytes)

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Locating a Block of DataLocating a Block of Data

Seek Time Latency Time Transfer Rate

Desiredtrack

Seek

Head

TransferLatency

Note: Access time = seek time + latency

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Seek time• The time for the head to move to the correct track• Specified as an average for all tracks on the disk surface

Latency time• The time for the correct block to arrive at the head once

the head is positioned at the correct track• Specified as an average, in other words, ½ the period of

rotation• Also called “rotational delay”

Access time is the time “to get to” the data (remember!)

• Access time = seek time + latency Transfer rate

• Same as throughput

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Disk Access TimesDisk Access Times

Avg. Seek timeaverage time to move from one track to another

Avg. Latency timeaverage time to rotate to the beginning of the sectorAvg. Latency time = ½ * 1/rotational speed

Transfer time1/(# of sectors * rotational speed)

Total Time to access a disk blockAvg. seek time + avg. latency time + avg. transfer time

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Latency ExampleLatency Example

A hard disk rotates at 3600 rpm What is the average latency?

Period of rotation = (1 / 3600) minutes= (1 / 3600) 60 seconds= 0.01667 s= 16.67 ms

Average latency = 16.67 / 2 ms= 8.33 ms

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Factors Determining Transfer Factors Determining Transfer RateRate

Transfer rate can be determined, given…

Rotational speed of the disk platters Number of sectors per trackNumber of bytes per sector

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Transfer Rate: ExampleTransfer Rate: Example

Q: Determine the transfer rate, in Mbytes/s, for a hard disk drive, given

Rotational speed = 7200 rpmSectors per track = 30Data per sector = 512 bytes = 0.5 Kbytes

A: Transfer rate = 7200 x 30 = 216,000 sectors/min

= 216,000 x 0.5 = 108,000 Kbytes/min

= 108,000 / 60 = 1,800 Kbytes/s

= 1,800 / 210 = 1.76 Mbytes/s

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Exercise - Transfer RateExercise - Transfer Rate

Q: Determine the transfer rate, in Mbytes/s, for a hard disk drive, given• Rotational speed = 7000 rpm• Sectors per track = 32• Data per sector = 1024 bytes

Skip answer Answer

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Exercise - Transfer RateExercise - Transfer Rate

Q: Determine the transfer rate, in Mbytes/s, for a hard disk drive, given• Rotational speed = 7000 rpm• Sectors per track = 32• Data per sector = 1024 bytes = 1 Kb

A: Transfer rate = 7000 x 32 = 224,000 sectors/min

= 224,000 x 1 = 224,000 Kbytes/min= 224,000 / 60 = 3,733 Kbytes/s= 3,733 / 210

= 3.65 Mbytes/s

Answer

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Typical Spec’sTypical Spec’s

Specification 3 ½” Floppy 2 GB Hard Disk

Platters/heads 1 / 2 5 / 9

Cylinders 80 4160

Sectors/track 18 Varies

Block size 512 512

Capacity 1.44 MB 2.1 GB

Rotation speed 360 rpm 7200 rpm

Avg. seek time 95 ms 8.5 ms

Latency 83 ms 4.2 ms

Transfer rate 54 Kbyte/s 10 Mbyte/s

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Track FormatTrack Format

Format of each track:

dataheadergap gap

CRC

SectorPrevious sector Next sector

Inter-blockgap

Inter-blockgap

Note:

CRC stands for “cyclic redundancy check”. It’s the “footer” at the end of each sector. CRC is a sophisticated form of parity for checking that the data read are accurate

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Disk Block FormatsDisk Block Formats

Single Data BlockSingle Data Block

Header for Windows Header for Windows diskdisk

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Disk FormattingDisk Formatting

The track positions, blocks, headers, and gaps must be established before a disk can be used

The process for doing this is called “formatting”

The header, at the beginning of each sector, uniquely identifies the sector, e.g., by track number and sector number

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Disk ControllerDisk Controller

Interface between the disk drive and the system is known as a “disk controller”

A primary function is to ensure data read/write operations are from/to the correct sector

Since data rate to/from the disk is different than data rate to/from system memory, “buffering” is needed

May also require special driver,as in CD-ROMs

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BufferingBuffering

System Diskcontroller

DiskRAM Buffer

(RAM)

1. Read data from disk into a buffer in the disk controller

2. Transfer data from buffer to system RAM (Note: this is a DMA operation)

Example: Reading data from a disk

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Multi-block Transfers (1 of 2)Multi-block Transfers (1 of 2)

The smallest transfer is one block (e.g., 512 bytes) However, often multi-block transfers are required The inter-block gap provides “time” for the

controller electronics to adjust from the end of one sector to the beginning of the next

“time” may be needed for a few reasons:Compute and/or verify the CRC bytesSwitch circuits from read mode to write mode

During a write operation the header is “read” but the data are “written”(Remember, the header is only “written” during formatting.)

Perform a DMA operation

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Multi-block Transfers (2 of 2)Multi-block Transfers (2 of 2)

Sometimes, sectors simply cannot be read or written consecutively

There is not enough time (see preceding slide)

The result is lost performance because the disk must undergo a full revolution to read the next sector

The solution: interleaving

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Data Block FormatInterblock gapHeaderDataFormatting disk

Disk Interleaving Disk Arrays

RAID – mirrored, stripedMajority logic fault-tolerant computers

Disk InterleavingDisk Interleaving

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InterleavingInterleaving

Rather than numbering blocks consecutively, the system skips one or more blocks in its numbering

This allows multi-block transfers to occur as fast as possible

Interleaving minimizes lost time due to latency

Interleaving “factor” (see next slide) is established when the disk is formatted

Can have a major impact on system performance

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Interleaving ExamplesInterleaving Examples

21 3 54 6 87 9

1 2 3 4 5

1 2 3

1:1 etc.

etc.

etc.

2:1

3:1

Factor

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2:1 Interleaving2:1 Interleaving

1

2 6

7

3

84

9

5

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File System ConsiderationsFile System Considerations

There is no direct relationship between the size and physical layout of blocks on a disk drive and the size and organization of files on a system

File systemDetermines the organization of information on a computerPerforms logical-to-physical mapping of informationA file system is part of each and every operating system

Logical mappingThe way information is perceived to be stored

Physical mappingThe way information is actually stored

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Alternate Disk TechnologiesAlternate Disk Technologies

Removable hard drivesDisk pack – disk platters are stored in a plastic case that is removableAnother version includes the disk head and arm assembly in the case

Fixed-head disk drivesOne head per trackEliminates the seek time

Bernoulli Disk DrivesHybrid approach that incorporates both floppy and hard disk technologyZip drives

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Removable hard disksRemovable hard disks

Also called “disk packs” A stack of hard disks enclosed in a metal or

plastic removable cartridge Advantages

• High capacity and fast, like hard disk drives• Portable, like floppy disks

Disadvantage• Expensive

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Fixed headsFixed heads

Fewer tracks but eliminates seek time

Disk Spindle Moving head

Fixed heads

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R.A.I.D. = Redundant array of R.A.I.D. = Redundant array of inexpensive disksinexpensive disks

A category of disk drive that employs two or more drives in combination for fault tolerance and performance

Frequently used on servers, but not generally used on PCs

There are a number of different R.A.I.D. “levels” (next slide)

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R.A.I.D. Levels (1 of 2)R.A.I.D. Levels (1 of 2)

Level 0Provides “data striping” (spreading out blocks of each file across multiple disks)No redundancyImproves performance, but does not deliver “fault tolerance”

Level 1Provides “data mirroring”: (a.k.a.: “shadowing”)Data are written to two duplicate disks simultaneouslyIf one drive fails, the system can switch to the other without loss of data or serviceDelivers fault tolerance

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R.A.I.D. Levels (2 of 2)R.A.I.D. Levels (2 of 2)

Level 3Same as level 0, but also reserves one dedicated disk for error correction dataGood performance, and some level of fault tolerance

Level 5Data striping at the byte level and stripe error correction informationExcellent performance, good fault tolerance

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Fault ToleranceFault Tolerance

The ability of a computer system to respond gracefully to unexpected hardware or software failure

Many levels of fault tolerance• E.g., the ability to continue operating in the

event of a power failure Some systems “mirror” all operations

• Every operation is performed on two or more duplicate systems, so if one fails, another can take over

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Data Mirroring (Shadowing)Data Mirroring (Shadowing)

A technique in which data are written to two duplicate disks simultaneously

If one disk fails, the system can instantly switch to the other disk without loss of data or service

Used commonly in on-line database systems where it is critical that data are accessible at all times

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Data StripingData Striping

A technique for spreading data over multiple disks

Speeds operations that retrieve data from disk storage

Data are broken into units (blocks) and these are spread across the available disks

Implementations allow selection of data units size, or stripe width

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Magnetic TapeMagnetic Tape

Offline storage Archival purposes Disaster recovery (backup) Tape Cartridges

20 – 144 tracks (side by side)Read serially (tape backs up)QIC – quarter inch cartridge (larger size)DAT – digital audio tape (small size)Size typically includes (2:1 compression)

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Types of Tape DrivesTypes of Tape Drives

Two types:Reel-to-reel

Used on mainframe computers

Cartridge (including cassette, VHS)Used on PCs

In either case, the tape can be removed from the drive (i.e., the tape drive supports offline storage)

When a tape is loaded in a tape drive and is ready to be accessed, the tape is mounted

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Reel to Reel Tape DriveReel to Reel Tape Drive

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Tape ReelsTape Reels

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Tape Reel SpecificationsTape Reel Specifications

Reel diameter: 10 ½” Tape width: ½” Tape length: 2400 feet Number of tracks: 9 Drive has nine read/write heads

9 bits of data are read/written at a time (8 data + parity)Each group of nine bits is called a frame

Data density/capacity1600 frames/inch 2400 x 12 x 1600 = 46,080,000 bytes/reel6250 frames/inch 2400 x 12 x 6250 = 1,800,000,000 bytes/reel

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Nine-track Tape LayoutNine-track Tape Layout

Physicalrecord

Inter-recordgap

1 byte of data(8 data bits + parity)

Track 1

Track 9

½”

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Tape CartridgeTape Cartridge

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Types of Tape CartridgesTypes of Tape Cartridges

QIC (Quarter Inch Cartridge) DAT (Digital Audio Tape)

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QIC (Quarter Inch Cartridge)QIC (Quarter Inch Cartridge)

Pronounced: quick Introduced in 1970s Popular format for backing up personal

computers Two general classes

Full-sized, 5¼” (also called “data cartridge”)Mini-cartridge, 3½”

Capacities up to 10 GB

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DAT (Digital Audio Tape)DAT (Digital Audio Tape)

Tape width: 8 mm or 4 mm Uses helical scan technique to record

data (like VCRs) Capacities to 24 GB (4 mm) or 40 GB

(8 mm)

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Optical StorageOptical Storage

Uses light generated by lasers to record and retrieve information

Information is stored by varying the light reflectance characteristics of the medium

Reflected light off a mirrored or pitted surface CD-ROM

Spiral 3 miles long, containing 15 billion bits!CLV – all blocks are same physical lengthBlock – 2352 bytes

2k of data (2048 bytes)16 bytes for header (12 start, 4 id)288 bytes for advanced error control

DVD-ROM4.7G per layerMax 2 layers per side, 2 sides = 17G

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CD-ROMCD-ROM

CD-ROM stands for “compact disc, read-only memory”

Evolved from audio CDs Disk size: 120 mm (5¼”) Capacity: 550 MB

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CD-ROMsCD-ROMs

Seek Time(milliseconds)

Single-Speed 600 150K per second

2X 320 300K per second

3X 250 450K per second

4X 135-180 600K per second

6X 135-180 900K per second

8X 135-180 1.2 MBps

10X 135-180 1.6 MBps

12X 100-150 1.8 MBps

16X 100-150 2.4 MBps (maximum)

24X 100-150 3.6 Mbps (maximum)

32X 100-150 4.8 Mbps (maximum)

General Speed Data Transfer Rate

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Layout: CD-ROM vs. Standard DiskLayout: CD-ROM vs. Standard Disk

CD-ROM Hard Disk

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CD-ROM vs. Magnetic DiskCD-ROM vs. Magnetic Disk

CD-ROM Magnetic Disk One spiral track (3

miles long!) Multiple tracks of

concentric circles Constant bit density Variable bit density Disk speed varies

(CLV, constant linear velocity)

Disk speed constant (CAV, constant angular velocity)

Constant transfer rate Constant transfer rate

Capacity: 550 MB Capacity: varies

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CD-ROM Data OrganizationCD-ROM Data Organization

270,000 blocks of 2048 bytes each (typically)

270,000 2048 = 552,960,000 bytes Extensive error checking and correction

(e.g., bad regions of the disk flagged) Substantial overhead for error correction

and identifying blocks Capacity can be as high as 630 MB

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Optical StorageOptical Storage

Laser strikes land: light reflected into detector Laser strikes a pit: light scattered

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Pits and Lands (1 of 2)Pits and Lands (1 of 2)

Data are stored as “pits” and “lands” These are burned into a master disk by a

high powered laser Master disk is reproduced mechanically by

a stamping process. ( Like a coin, sort of ) Data surface is protected by a clear coating Data are read by sensing the reflection of

laser lightA pit scatters the lightA land reflects the light

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Pits and Lands (2 of 2)Pits and Lands (2 of 2)

Laser

Land

Reflectedlight

LaserLaser

Pit

Scatteredlight

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CD-ROM Read ProcessCD-ROM Read Process

Laserdiode

Prism

Light detector

Land Pit

Transparentprotective layer

More detail

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WORM Disks and DrivesWORM Disks and Drives

WORM = Write-once, read many Also called CD-R, for CD Recordable Begin with blank CDs WORMs drives are used to write the CD The write process is irreversible Many standards, some disks may be read

on standard CD-ROM drive, others may not Applications

Infrequent data distributionSmall quantitiesFor large quantities, cheaper to have CD-ROMs manufactured

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Magneto OpticalMagneto Optical

Disk may be written, read, and rewritten Write process is preformed at high

temperature Combines features of optical and magnetic

technology Data are stored as a magnetic charge on

the disk surface During reading, the polarity of the reflected

light is sensed (not the intensity)

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DisplaysDisplays

Pixel – picture element Size: diagonal length of screen Resolution (pixels on screen)

VGA: 480 x 640SVGA: 600 x 800768 x 10241280 x 1024

Picture size calculationResolution * bits required to represent number of colors in pictureExample: 16 color image, 100 pixels by 50 pixels

4 bits (16 colors) * 100 * 50 = 20,000 bits

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PixelsPixels

A Pixel is a “picture element”a single point in a graphic imageA graphics display is divided into thousands (or millions) of pixels arranged in rows and columnsThe pixels are so close together, they appear connectedThe number of bits used to represent each pixel determines how many colours or shades of grey can be representedFor a B&W (black and white) monitor, each pixel is represented by 1 bitWith 8 bits per pixel, a monitor can display 256 shades or grey or 256 colours (Note: 28 = 256)

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Display SizeDisplay Size

Usually specified in “inches” and measured diagonally

Value cited is the diagonal dimension of the raster -- the viewable area of the display

E.g., a 15” monitor: ( v.i.s. = ?? 13.6? )

15”

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Display ResolutionDisplay Resolution

Resolution is the number of pixels on a screen display

Usually cited as n by mn is the number of pixels across the screenm is the number of pixels down the screen

Typical resolutions range from…640 by 480 (low end), to1,600 by 1,200 (high end)

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Video RAM RequirementsVideo RAM Requirements

Total number of pixels is n m Examples

640 480 = 307,200 pixels1,600 1,200 = 1,920,000 pixels

Video RAM required equals total number of pixels times the number of bits/pixel

Examples640 480 8 = 2,457,600 bits = 307,200 bytes = 300 Kbytes1,600 1,200 24 = 46,080,000 bits = 5,760,000 bytes = 5,625 Kbytes = 5.49 Mbytes

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Video RAM (KB) Per ImageVideo RAM (KB) Per Image

ResolutionBits per pixel

8 bit 16 bit 24 bit

640 x 480 300 600 900

800 x 600 468.75 937.5 1406.25

1024 x 768 768 1536 2304

1152 x 1024

1152 2304 3456

1280 x 1024

1280 2560 3840

1600 x 1200

1875 3750 5625

See previous slide for calculations

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Aspect RatioAspect Ratio

Aspect ratio is the ratio of the width to height of a display screen

4:3 on most PCs16:9 on high definition displays

For a 640 by 480 display, the aspect ratio is 640:480, or 4:3

Related termsLandscape

The width is greater than the height

PortraitThe height is greater than the width

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Dot PitchDot Pitch

Dot pitch is a measure of the diagonal distance between phosphor dots (pixels) on a display screen

One of the principal characteristics that determines the quality of a display

The lower the number, the crisper the image Cited in mm (millimeters) Typical values range from 0.15 mm to 0.30 mm Note

Dot pitch, as specified, is the capability of the displayFor a particular image, dot pitch can be calculated as…

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Dot Pitch Image: ExampleDot Pitch Image: Example

Q: What is the dot pitch of an image displayed on a 15” monitor with a resolution of 640 by 480?

A:

640

480Z1. Z = (6402 + 4802)1/2 = 800

2. 1 mm = 0.039 inch

Dot pitch = 15 / 800 inches= 0.01875 inches= 0.01875 / 0.039 mm= 0.481 mm

Notes:

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Dot Pitch IllustratedDot Pitch Illustrated

Pixel

0.481 mm

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Dot Pitch Image TableDot Pitch Image Table

ResolutionDisplay Size

14” 15” 17” 19” 21”

640 x 480 0.45 0.48 0.54 0.61 0.67

800 x 600 0.36 0.38 0.44 0.49 0.54

1024 x 768 0.28 0.30 0.34 0.38 0.42

1152 x 1024 0.23 0.25 0.28 0.32 0.35

1280 x 1024 0.22 0.23 0.27 0.30 0.33

1600 x 1200 0.18 0.19 0.22 0.24 0.27

Note: Dot pitch figures in mm (millimeters)

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Colour and DisplaysColour and Displays

Pixel colour is determined by intensity of 3 colours – Red Green Blue or RGB

4 bits per colour16 x 16 x 16 = 4096 colours

24 bit color (True Colour)16.7 million colours

Video memory requirements are significant!

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Colour DisplaysColour Displays

CRT displayseach pixel is composed of three superimposed dots: red, green, and blueHence, RGB displayThe three dots are created by three separate beamsIdeally, the three dots should converge at the same point, however, in practice there is a small amount of convergence error, and this makes the pixels appear fuzzy

LCDsColour is created by filtering/blocking different frequencies of light

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CRT DisplayCRT Display

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Operation of a CRT DisplayOperation of a CRT Display

A CRT display contains a vacuum tube At one end are three electron guns, one

each for red, green, and blue At the other end is a screen with a

phosphorous coating The three electron guns fire electrons at

the screen and excite a layer of phosphor Depending on the beam, the phosphor

glows, either red, green, or blue

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Operation of an LCDOperation of an LCD

Two sheets of polarizing material with a liquid crystal solution between them

An electric current passed through the liquid causes the crystals to align so that light cannot pass through them

Each crystal, therefore, acts like a shutter, either allowing light to pass through or blocking the light

Operation1st filter polarizes light in a specific directionElectric charge rotates molecules in liquid crystal cells proportional to the strength of colorsColour filters only let through red, green, and blue lightFinal filter lets through the brightness of light proportional to the polarization twist

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Liquid Crystal DisplayLiquid Crystal Display

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Colour Transformation TableColour Transformation Table

With 8 bits per pixel, there is no way to represent red, green and blue colours separately

256 arbitrary combinations are chosen to form a palette of colours

A value from 0-255 represents the colour of a pixel Table holds the RGB values for each of the 256

possible colours To display a pixel, the system reads the RGB values

from the table and converts to screen colour With 16 bits per pixel, the table represents 64,000

colours With 24 bits per pixel, no table is needed: 8 bits per

each RGB colour

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Colour Transformation TableColour Transformation Table

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Raster scanRaster scan

Scanning and displaying each pixel , one row at a time, from left to right

More than 30 times a second Interlacing

Less demanding on the monitor (each row is displayed half as often)Flickering

Noninterlacing (progressive scan)

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InterlacingInterlacing

Interlacing is an image drawing technique whereby the electron guns draw only half the horizontal lines with each pass

The odd lines are drawn on the 1st pass, the even lines are drawn on the 2nd pass

A non-interlaced imaged is completely drawn in one pass

Let’s see…

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Interlacing AnimationInterlacing Animation

Non-interlaced scanning Interlaced scanning

Electron beam “on” (drawing)

Electron beam “off” (retracing)

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Raster Screen GenerationRaster Screen Generation

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Display: ExampleDisplay: Example

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Scan FrequencyScan Frequency

Horizontal scan frequencyThe frequency with which an electron beam moves back-and-forthThe rate of drawing each line in an imageTypical range: 30-65 kHz

Vertical scan frequencyThe frequency with which an electron beam moves up-and-downAlso called vertical refresh rate , refresh rate, vertical frequency, vertical scan rate, or frame rateThe rate of drawing imagesTypical range: 45-120 Hz

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Multi-scan MonitorsMulti-scan Monitors

A multi-scan monitor can adjust to the horizontal and vertical scan frequencies of the video signal produced by the interface

Also called multi-sync, multi-frequency, or variable-frequency monitors

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Video FrequencyVideo Frequency

The frequency at which pixels are drawn on the display

Specified as a maximum capability of the monitor

Also called video bandwidth Typical ranges 50-100 MHz

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Video Frequency vs. Resolution Video Frequency vs. Resolution and Frame Rateand Frame Rate

Video Frequency > Resolution Frame Rate

Example: Daewoo CMC-1703B specifications: Video frequency = 85 MHz Max resolution = 1280 by 1024 @ 60Hz

Note: 1280 1024 60 = 78,643,200 = 78.6 MHz

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PrintersPrinters

Output as dots (like pixels in displays) Dots vs. pixels

300-2400 dpi vs. 70-100 pixels per inchDots are on or off, pixels have intensitiesIntensity of dots is fixedTo create a gray scale, it is necessary to congregate groups of dots into a single equivalent point and print different numbers of them to approximate different colour intensities

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Creating a Gray ScaleCreating a Gray Scale

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PrintersPrinters

Four main types:ImpactLaserInk jetThermal dye transfer and thermal wax transfer

Impact

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Impact vs. Non-ImpactImpact vs. Non-Impact

Impact printers physically transfer a dot or shape to the paper

Include dot-matrix, belt, & solid line printers

Non-impact printers spray or lay down the image

Impact printers remain important because they can print multi-part forms (e.g.: carbon or NCR copies)

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PrintersPrinters

Four main types:Dot matrix (sample impact)LaserInk jetThermal dye transfer and thermal wax transfer

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How it worksHow it works( Impact Type Dot-Matrix )( Impact Type Dot-Matrix )

A print-head moves back-and-forth in front of forms (paper) on which characters or graphic images are transferred. The print-head contains numerous wires, typically from 9 to 24. Each wire is part of a solenoid-like unit. An electrical pulse applied to the solenoid creates a magnetic field which forces the wire to move briefly forward then backward. As the wire moves forward, it strikes a print ribbon containing ink. The impact transfers an ink dot to the paper. The paper is supported from behind by a platen (a hard flat piece)

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IllustrationIllustration

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Dot Matrix Print HeadDot Matrix Print Head

Front view Side view

Print wires(e.g., 12)

One print wire

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Dot Matrix Impact PrintingDot Matrix Impact Printing

Printwire

Ribbon

Paper

Platen

Side view Front view

Paper

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SpecificationsSpecifications

cpscharacters per secondVaries by quality of print (e.g., draft vs. final (NLQ))

lpmlines per minute (related to cps)

FormsMaximum number of layers of paper that can by printed simultaneouslySpecified as n-part forms (e.g., 4-part forms)

mtbfMean time between failure (e.g., 6000 hours)

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Dot Matrix Printer: Example - 1Dot Matrix Printer: Example - 1

FormsMaster 8000 by Printek, Inc.

http://www.printek.com

Specifications

• 800 cps

• 400 lpm

• 6-part forms (max)

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Dot Matrix Printer: Example - 2Dot Matrix Printer: Example - 2

Pacemaker 3410 by OKI Data, Inc.

http://www.okidata.com

Specifications

• Printhead wires: 9

• Printhead life: 200 million characters

• Print speed:

• near letter quality: 105 cps

• utility: 420 cps

• high speed draft: 550 cps

• Number of copies: 8

• MTBF: 8000 hours @ 25% duty cycle, 35% density

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PrintersPrinters

Four main types:Dot matrixLaserInk jetThermal dye transfer and thermal wax transfer

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Laser Printer OperationLaser Printer Operation

1. Dots of laser light are beamed onto a drum2. Drum becomes electrically charged3. Drum passes through toner which then sticks

to the electrically charged places4. Electrically charged paper is fed toward the

drum5. Toner is transferred from the drum to the

paper6. The fusing system heats and melts the toner

onto the paper7. A corona wire resets the electrical charge on

the drum

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First stepFirst step

A laser is fired in correspondence to the dots to be printed. A spinning mirror causes the dots to be fanned out across the drum. The drum rotates to the next line, usually 1000th or 1600th of an inch.

The drum is photosensitive. As a result of the laser light, the drum becomes electrically charged wherever a dot is to be printed.

Laser

Spinningmirror

Photosensitivedrum

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Second stepSecond step

2. As the drum continues to rotate, the charged part of the drum passes through a tank of black powder called toner. Toner sticks to the drum wherever the charge is present. Thus, the pattern of toner on the drum matches the image.

Toner

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Third stepThird step

3. A sheet of paper is fed toward the drum. A charge wire coats the paper with electrical charges. When the paper contacts the drum, it picks up the toner from the drum

Paper

Chargewire

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Fourth stepFourth step

4. As the paper rolls from the drum, it passes over a heat and pressure area known as the fusing system. The fusing system melts the toner to the paper. The printed page then exits the printer.

As the same time, the surface of the drum passes over another wire, called a corona wire. This wire resets the charge on the drum, to ready it for the next page.

Coronawire

Fusingsystem

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SpecificationsSpecifications

ppmPages per minuteTypically 4-10 ppm

dpiDots per inchTypically 600-1200 dpi

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Laser Printer: ExampleLaser Printer: Example

Laserjet 5000 Series from Hewlett Packard Co.

(http://www.hp.com)

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PrintersPrinters


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BackgroundBackground

Inkjet technology was developed in the 1960s

First commercialized by IBM in 1976 with the 6640 printer

Cannon and Hewlett Packard developed similar technology

Also called bubble jet

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How it worksHow it works

Characters and graphics are 'painted‘ line by line to from a pattern of dots as a print head scans horizontally across the paper. An ink-filled print cartridge is attached to the inkjet's print head. The print head contains 50 or more ink-filled chambers, each attached to a nozzle. An electrical pulse flows through thin resistors at the bottom of each chamber. When current flows through a resistor, the resistor heats a thin layer of ink at the bottom of the chamber to more than 900 degrees Fahrenheit for several millionths of a second . The ink boils and forms a bubble of vapour. As the vapour bubble expands, it pushes ink through the nozzle to form a droplet at the tip of the nozzle. The droplet sprays onto the paper.

The volume of the ejected ink is about one millionth that of a drop of water from an eye-dropper. A typical character is formed by an array of these drops 20 across and 20 high. As the resistor cools, the bubble collapses. The resulting suction pulls fresh ink from the attached reservoir into the firing chamber.

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Inkjet Printer: ExampleInkjet Printer: Example

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PrintersPrinters


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How it worksHow it works

Thermal dye transfer printers, also called dye sublimation printers, heat ribbons containing dye and then diffuse the dyes onto specially coated paper or transparencies. These printers are the most expensive and slowest, but they produce continuous-tone images that mimic actual photographs. Note that you need special paper, which is quite expensive. A new breed of thermal dye transfer printers, called snapshot printers, produce small photographic snapshots and are much less expensive than their full-size cousins.

Thermal wax transfer printers use wax-based inks that are melted and then laid down on regular paper or transparencies. Unlike thermal dye transfer printers, these printers print images as dots, which means that images must be dithered first. As a result images are not quite photo-realistic, although they are very good. The big advantages of these printers over thermal dye transfer printers are that they don't require special paper and they are faster.

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DitheringDithering

Dithering is creating the illusion of new colours and shades by varying the pattern of dots. Newspaper photographs, for example, are dithered. If you look closely, you can see that different shades of grey are produced by varying the patterns of black and white dots. There are no grey dots at all. The more dither patterns that a device or program supports, the more shades of grey it can represent. In printing, dithering is usually called halftoning, and shades of grey are called halftones. Example: traditional B & W newspaper.

Note that dithering differs from grey scaling. In grey scaling, each individual dot can have a different shade of grey.

black grey light grey white

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Scanner: How it worksScanner: How it works

A scanner works by digitizing an image. A scanning mechanism consists of a light source and a row of light sensors. As 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. Colour filters can be used to produce colour images, either by providing multiple sensors or by scanning the image three times with a separate colour filter for each pass. The resolution of scanners is similar to that of printers, approximately 300-600 dpi (dots per inch).

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ScannersScanners

Three main typesFlatbedSheet-fedHandheld

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Flatbed Scanner: ExampleFlatbed Scanner: Example

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Sheet-fed Scanner: ExampleSheet-fed Scanner: Example

OfficeJet Series 700 from Hewlett Packard Co

(http://www.hp.com)

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Handheld Scanner: ExampleHandheld Scanner: Example

QuickScan GP Bar Code Scanner from PSC, Inc.

(http://www.pscnet.com)

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Pointing DevicesPointing Devices

User Input DevicesKeyboard, mouse, light pens, graphics tablets

Communication DevicesTelephone modemsNetwork devices

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Computer Humour Computer Humour

http://www.funnyhumor.com/pictures/217.php

1 Lecture 10 Computer Peripherals ITEC 1000 “Introduction to Information Technology”

Documents

cpuexpanded storage

floppy disk drives

pcmciastorage devices

reelstorage devices

kbytess reel

floppy drivescdrom

flexible disks

kbytess cartridge200