Lecture 2:
Secondary Storage, Input and Output
Devices
Dr Yingchao ZHAO

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After this lecture, you should be able to:
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Describe the different types of secondary storage devices
Be aware of the existence of different input devices and their basic mechanisms.
Be aware of the existence of different output devices and their basic mechanisms.

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Storage holds data, instructions, and information for future use.
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Storage medium is the physical material on which a computer keeps data, instructions, and information.
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Two key areas in evaluating storage systems:
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Capacity
Access time

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Capacity is the number of bytes a storage medium can hold.
This shows common units for counting size.
From Wikipedia

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What can be stored in 1TB space?
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500,000,000 pages of text
285,000 digital photos
250,000 songs
120 hours of digital video

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One of the most popular secondary storage.
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Mainly magnetic disks.
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Properties:
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Random access – at any time, any part on HD can be accessed.
High capacity – up to TB
Medium access time (several ms) – ~100000 times slower than RAM, ~100 times faster than DVD.
Data stored on hard disks are first loaded into RAM before being processed or displayed.

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A head crash occurs when a read/write head touches the surface of a platter.
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E.g., when something happened suddenly (power off, detach, fall down, etc.) during read/write.
Read/write head is really close to the platters!

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If a HD crashes, data inside it cannot be retrieved by normal OS.
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Recovery is costly!
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> $1000 for simple cases and >$10000 for more complex cases
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Recovery of data is not guaranteed.
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Imagine the case where the read/write head scratched a portion of disk platter. No way to recover the data stored inside.

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Hard disks must be formatted before use
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The OS can then read/write files on the disks.
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Different OSes format disks to different formats, e.g.,
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FAT32 / NTFS for Windows ext4 for Linux / UNIX
HFS+ for MacOS
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New HDs are usually formatted before put on shelves.

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RAID ( redundant array of independent
(inexpensive) disks ) is a group of two or more integrated hard disks.
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Data are duplicated automatically.
Data can be recovered even if one HD fails.
Faster read access.
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A network attached storage
( NAS ) device is a server connected to a network with the sole purpose of providing storage.

An external hard disk is a separate freestanding hard disk that connects to your computer with a cable or wirelessly
A removable hard disk is a hard disk that you insert and remove from a drive
Internal and external hard disks are available in miniature sizes ( miniature hard disks )
SATA EIDE
SCSI SAS
A disk controller sits between a hard disk and other parts in the computer like memory or CPU
- Consists of a special-purpose chip and electronic circuits.
- Control the transfer of data to and from the disk through system bus.
Common disk controllers include:

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Flash memory chips are a type of solid state media (like EEPROM)
Non-volatile
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No moving parts (unlike hard disks)
In the form of flash cards or solid state drives
( SSD )
SSD is better than HD (and more expensive) in the areas that:
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Shorter access time
Higher transfer rates
Generate less heat and consume less power
Last longer

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A memory card is a removable flash memory device that you insert and remove from a slot in a computer, a mobile device or a card reader/writer.
from Wikipedia from Wikipedia from Wikipedia from Wikipedia

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SD Cards (SD, SDHC, SDXC)
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One of the most commonly used flash cards
Current SDHC cards may have capacity of 128GB
Different form factors: SD, Mini SD, Micro SD
Memory Stick (Duo, PRO Duo, PRO-HG)
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Originated from, and mainly used in Sony
Compact Flash (CFast)
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Much faster than SD, more expansive
Mainly used in high-end digital camera xD-Picture Card
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Originated from Olympus & Fujifilm
Fading out
See this for a comparison of memory cards http://en.wikipedia.org/wiki/Comparison_of_memory_cards

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USB flash drives (or, thumb drives) are plugged into a USB port on a computer.
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It’s very convenient:
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Small, light-weight, removable, rewritable.
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But, handle with care!
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Security is a big concern.
Have you heard about the news about privacy data leakage through unattended USB thumb drives?

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An optical disc consists of a flat, round, portable disc made of metal, plastic, and lacquer that is written and read by laser.
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Typically store software, data, digital photos, movies, music, etc. (mainly for archive)
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Read only vs. rewritable
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DVD vs. DVD-R, DVD+R vs.
DVD-RW, DVD+RW, DVD-RAM

A CD-ROM can be read from but not written to
• Read from a CD-ROM drive or CD-ROM player
• A capacity of 650MB
A CD-R is a multisession optical disc on which users can write, but not erase
• You may delete files, but the location can’t be used to store other data.
A CD-RW is an erasable multisession disc
• Must have a CD-RW drive

A DVD-ROM is a high-capacity optical disc on which users can read but not write or erase
• Requires a DVD-ROM drive, capacity : 4.7-17 GB
• Single-sided, double-sided, single-layered, double- layered.
The most updated optical disc standard. A
Blu-ray Disc-ROM (BD-ROM) has a storage capacity of 100 GB. Usually stores HD video.
DVD-RW, DVD+RW, and DVD+RAM are highcapacity rewritable DVD formats

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Tape is a magnetically coated ribbon of plastic. It is capable of storing large amounts of data and information.
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A tape drive reads and writes data and information on a tape sequentially.

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A magnetic strip card contains a magnetic strip that stores information.
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A smart card stores information on a thin microprocessor embedded in the card.

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Input (noun) is any data and instructions entered into the memory of a computer.
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An input device is any hardware component that allows users to enter data and instructions into a computer.

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A keyboard is an input device that contains keys on which a user presses to enter input.
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A standard input device in most of the computers.
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> 100 keys
Wired or wireless
Small or virtual keyboards on mobile devices.
Wired
Keyboards
USB port
Keyboard port
Wireless
Keyboards
Bluetooth
IrDA
Short range radio

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A pointing device is an input device that allows a user to control a pointer on the screen
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A pointer is a small symbol on the screen whose location and shape change as a user moves a pointing device
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A mouse is a pointing device that fits under the palm of your hand comfortably
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Most widely used pointing device on desktop computers
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A mouse can be wired or wireless

• A trackball is a stationary pointing device with a ball on its top or side
• A touchpad is a small, flat, rectangular pointing device that is sensitive to pressure and motion
• A pointing stick is a pressure-sensitive pointing device shaped like a pencil eraser positioned between keys on a keyboard

Microsoft Surface

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Video games and computer games use game controllers as the input devices that direct movements and actions of on-screen objects
Gamepads
Joysticks and Wheels
Light guns Dance pads
Motionsensing controllers

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Digital camera
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A digital camera is a mobile device that allows users to take pictures and store them digitally.
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Scanner
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Flatbed
Pen or handheld
Sheet-fed drum
Flatbed Pen or
Handheld
Sheet-fed
Drum

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Factors affecting image quality include:
Resolution
• Dimensions of the image in terms of pixels.
• e.g., 640x480
(300k pixels),
3872x2592
(10M pixels)
No. of bits per pixel
• More bits  more colors, more grayshade levels.
• e.g.,
24-bit
Sensor (CCD) size
• Larger CCD  more light collected per pixel  more accurate color information
• e.g.,
½”, 1”, 4/3”,
35mm, etc.

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A Web cam is a type of digital video camera that enables a user to:
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Capture video and still images
Send e-mail messages with video attachments
Add live images to instant messages
Broadcast live images over the Internet
Make video telephone calls
A video conference is a meeting between two or more geographically separated parties.

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Voice input is the process of entering input by speaking into a microphone
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Voice recognition is the computer’s capability of distinguishing spoken words
Siri on iPhone 4S use your voice to send messages, schedule meetings, place phone calls, and more.

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Optical character recognition ( OCR ) involves reading characters from ordinary documents.
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A turnaround document is a document you return to the company that creates

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A bar code reader , also called a bar code scanner uses laser beams to read bar codes

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RFID ( radio frequency identification ) uses radio signals to communicate with a tag placed in or attached to an object.
In HK, we have Octopus card ( 八達通 ) which uses RFID technology
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An RFID reader reads information on the tag via radio waves
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RFID can track:
Inventory
Location of soldiers
Employee wardrobes
Airline baggage
Gauging tire pressure and temperature
Library books
Prepaid tolls

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Reads the magnetic stripe on the back of cards such as:
Credit cards
Entertainment cards
Bank cards
Other similar cards

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A magnetic ink character recognition (MICR) device reads text printed with magnetized ink.
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An MICR reader converts MICR characters into a form the computer can process.
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Bank industry uses MICR for check processing.

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Biometric authenticates a person’s identity by verifying a personal characteristic.
Fingerprint reader
Face recognition system
Hand geometry system
Voice verification system
Signature verification system
Iris recognition system
Retinal scanners

fingerprin t reader iris recognition system hand geometry system

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Output is data that have been processed into useful forms.

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An output device is any type of hardware component that conveys information to one or more people.
Display devices
Interactive whiteboards
Printers
Speakers, headphones, and earbuds
Data projectors
Force-feedback game controllers
Tactile output

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A display device visually conveys text, graphics and video information.
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A monitor is packaged as a separate peripheral.
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LCD monitors
LED monitors
Widescreen

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The quality of an LCD monitor or LCD screen depends primarily on:
Resolution Response time Brightness
Dot pitch Contrast ratio

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It is a screen that uses Light Emitting Diodes to portray different colored pixels. It has better contrast and is more efficient than the LCD Monitors which constantly has a flash lamp that is turned on and the Plasma and the old tube monitors.
The difference between LED and LCD is the back-light of the monitors. While the technology of the displays of LCD’s and LED’s is basically the same, the LCD monitor uses cold cathode fluorescent lamps as back-lights as compared to the LED monitors that emit diodes.
CRT
Monitor

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TV can also be used as an output device.
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May require a converter if you are connecting your computer to an analog computer.
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Digital televisions offer a crisper, higher-quality display.
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HDTV is the most advanced form of digital television.

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A printer produces text and graphics on a physical medium.
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Printed information is called a hard copy , or printout.
Landscape or portrait orientation

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A non-impact printer forms characters and graphics on a piece of paper without actually striking the paper.
Ink-jet printers
Mobile printers
Photo printers
Label and postage printers
Laser printers
Plotters
Thermal printers
Largeformat printers

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An ink-jet printer forms characters and graphics by spraying tiny drops of liquid ink onto a piece of paper.
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 black-and-white, or colors (CYMK)
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Cyan, Yellow, Magenta
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One key property of a printer is dpi
(dots per inch).

 Produce color photolab-quality pictures
 Mostly use ink-jet technology
 PictBridge allows you to print photos directly from a digital camera
 Support printing from a memory card and preview photos on a built-in LCD screen

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High quality
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High speed
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A thermal printer generates images by pushing electrically heated pins against the heat-sensitive paper.
Plotters are used to produce high-quality drawings.
Large-format printers create photo-realistic quality color prints on a larger scale.

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Impact printers from characters and graphics on a piece of paper by striking a mechanism against an inked ribbon that physically contacts the paper.

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A dot-matrix printer produces printed images when tiny wire pins on a print head mechanism strike an inked ribbon.
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Advantageous to print multiple copies at a time.
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A line printer prints an entire line at a time.

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A label printer is a small printer that prints on adhesive-type material
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A postage printer prints postage stamps
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Postage also can be printed on other types of printers

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An audio output device produces music, speech or other sounds.
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E.g.,
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Speakers, headphones, earbuds
A 5.1 surround sound speaker set.
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Usage of speakers:
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Generate high-quality sounds for playing games
Interact with multimedia presentations
Listen to music
View movies, etc.

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Headphones are speakers that cover our head or are placed outside your ears.
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Earbuds (also called earphones ) rest inside your ear canal.

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Some speakers are specifically designed to play audio from a portable media player.
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E.g., wireless speakers with dock.

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Voice output occurs when you hear a person’s voice or when the computer talks to you through the speakers (and microphones).
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Often works with voice input.
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E.g., VoIP, Site readers

They are available for specific uses and applications.
Data projectors
Interactive whiteboards
Forcefeedback game controllers
Tactile output

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A data projector is a device that takes the text & images displaying on a computer screen and projects them on a larger screen.
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E.g., digital light processing (DLP) projector
You’re now viewing a projector screen!

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An interactive whiteboard is a touchsensitive device, resembling a dry-erase board, that displays the image on a connected computer screen

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Force-feedback sends resistance to the device in response to actions of the user
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Tactile output provides the user with a physical response from the device

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Many accessibility options exist for users with various disabilities.
Magnifier
Braille printer

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DualShock and Wiimote, are they input devices? Or output devices? Why?

 Imagine, one day, your boss asks you to copy many data of a project to his client.
 As you know, the data files are about 2GB in size.
 How will you help to pass the data to your client? Why you choose that method or storage media?

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Different secondary storage devices in computer systems are introduced.
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Hard disk, SSD, Flash memory, USB thumb drive, magnetic tape.
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Common output devices include
 monitors, printers, speakers and projectors
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Various input devices can help us to instruct or provide data to the computer.
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Keyboard, mouse, track ball, voice input, web cam, scanner, OCR, biometric, etc.