2/13: Storage, Input & Output

• Data storage– Magnetic– Optical

• Input & Output: Definitions– Examples: Input & Output devices– Keyboards– Fonts– Image File Size: Color Depth,

Resolution– Monitors

Data storage: what is it?

• Long-term storage, not immediate memory

• Not RAM (short-term memory)

• Synonyms: secondary storage, auxiliary storage, mass storage

images courtesy of dalelabs.com,, iomega.com, imation.com,

Data storage: where is it?

• Storage involves 2 parts: the device & the media

• Removable vs. fixed media

• Where can you store data?– magnetic media– optical media– magneto-optical media– solid state media

image courtesy of How Computers Work

Storage characteristics• Random vs. sequential access• Tracks & sectors• Speed

– spin rate (RPM)– seek time & latency– access time– data transfer rate

• Storage Capacity– areal density– size

Image courtesy of How Computers Work

Magnetic data storage

• Use magnets to store bits:– example: 0 = N , 1 = S

• Reading and writing

• Floppy disk drives

• Hard disk drives

PACE

image courtesy of How Computers Work

Floppy disk drives: types

• Low-density floppy drives: 5.25” floppy disks3.5” 1.44 MB floppy disks

• High-density floppy drives: Zip disks, LS-120 disks

Images courtesy of How Computers Work, Imation.com, and Iomega.com

Floppy disk drives: how they work• Shutter opens with an arm.• Cookie spins on the spindle.• Read/write heads get close

to the cookie inside• Magnetic particles generate

electric currents in the heads.

• Electric currents are interpreted as a series of bits.

Images courtesy of How Computers Work

Hard disk drives: overview

• Glass platters coated with magnetic particles

• Read/write heads like floppy drives but much smaller

• Multiple platters, multiple heads.

Image courtesy of How Computers Work

Optical Storage• Instead of using magnetism to store bits, we use light• A laser is the light

– Laser: “light amplification by stimulated emission of radiation”

– Extremely focused, narrow beam of powerful light– Depending on the wavelength, the beam can be narrower or

wider

• Lands are flat areas on the disc– Reflect light like a mirror

• Pits are holes in the disc– Scatter light

Courtesy of http://www.microserve.net/~tpetchy/DVD.shtml

CD Drives: Types and Operation

• CD-ROM drive speeds: how many times faster than the original CD-ROM drives• 2x, 4x, 6x, 8x, 16x, 32x, 48x

• Operation:• Diode generates laser• Laser bounces off mirrors, reaching the disc• Disc reflects or scatters laser• Light-sensing diode sees the reflections, comparing

them to a timing circuit to generate 0s and 1s

Image courtesy of c-cube.com

Types of Optical Discs

• Compact discs:– CD-ROM: read only memory (680 MB)– CD-R: Recordable (650 MB)– CD-RW: ReWritable (495 MB)

Image courtesy of c-cube.com

Types of Optical Discs• Digital versatile discs – higher density storage

– DVD-ROM: read only memory (4.7 – 17 GB)– DVD-R: Recordable (3.9 GB?)– DVD-ram (5.2 GB) & DVD+RW (6.0 GB): Rewritable

(still fighting)

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Input & Output: Definitions

• Input: “to enter data into the computer for processing; the data entered.”

• Output: “to transfer data from the computer to devices that allow you to see, hear, or feel it; the data transferred.”

images courtesy of keytronic.com, viewsonic.com

What is the essential qualification?

• For something to be qualified as an input or output device, it must be an interface between the user and the computer.

• Cables, dial-up modems, etc. would NOT be input or output devices.

images courtesy of logitech.com, viewsonic.com

Input devices: examples

• keyboards fax modems

• pointing devices scanners

• microphones

images courtesy of logitech.com, keytronic.com, buy.com,

Output devices: examples

• monitors printers

• speakers feedback game controllers

Images courtesy of viewsonic.com, yamaha.com, logitech.com

The Keys on the Keyboard

• for inputting text

• Standard keyboard– alphanumeric keys – function keys (F1)– shift keys (left shift)– toggle keys (caps lock)– special function keys (enter, windows, menu, home,

end, page up/down, delete, backspace, esc)

You will be expected to know what the keys on the keyboard do.

Image courtesy of fentek-ind.com

Ergonomic Keyboards

• Ergonomics: how machines and humans interact, with an emphasis on bodily stress and fatigue.

• Ergonomic keyboards are designed to alleviate wrist strain -- particularly carpal tunnel syndrome.

images courtesy of fentek-ind.com and darwinkeyboards.com

Fonts• Types of fonts: typeface family: Arial, Times

Roman

• serifs: things on end of letters

• Types of fonts: style: regular, bold, italic, shadow

• size: measured in points (72 pts/in)

F Fserifs

Arial, 208 pt., italic

Times New Roman, 229 pt., regular

Image File Size: Contributors• Images are stored on a per-bit

basis:– Bigger the physical image =

bigger the file size– Deeper the color depth = bigger

the file size– Higher the resolution = bigger

the file size 8-bit color 35K

50% size 10K

Lower res 51K

Original 56K

Color Depth

• Color depth is the number of bits that are stored for each pixel

• 1-bit B&W– line art– halftone

• 8-bit grayscale

• 24-bit color

Pictures appear courtesy of Mustek http://www.mustek.com.tw/Support/html/scannings.html

1 bit line art 1 bit halftone

8-bit grayscale 24-bit color

Why 24-bit Color?

• Color is stored as the combination of three colors: red, green, & blue (RGB).

• Each color has a value stored for it using 8 bits.

• 3 colors x 8 bits = 24 bits total.

• How many levels for each color can be recorded?– 8 bits per color = 2 to the 8th power = ?

Resolution: Printers & Files

• resolution: dpi dots per linear inch

• horizontal resolutionmay differ from vertical resolution

• higher the resolution, the “truer” the image.

• monitors: 50-100 dpiprinters (inkjet): 100-200 dpiprinters (laser): 300-1200 dpi

George Seurat, Sunday Afternoon on La Grande Jatte from Art.com

300 dpi: no zoom, 400% zoom 150 dpi: no zoom, 400% zoom

Resolution

How Monitors Work

• Resolution

• Refresh Rate

• Raster• scan lines

• field

• Flat-panel displays                                                                                                                              

image courtesy of sonystyle.com

How many colors are there?

Name colors possible mode

Standard VGA 16 4 bit

256 color mode 256 8 bit

High Color 65,536 16 bit

True Color 16,777,216 24 bit

Terms

• Resolution: # pixels displayed horizontally and vertically

• Refresh rate: how quickly the image is redrawn

Raster scanning

• Raster: the area that is hit by the electron beams, line by line. Each line is called a scan line.

• Field: a complete sweep of the screen.

• Refresh: rate usually at least 60/sec (60 Hz)

Flat-panel LCD Displays

• Passive-matrix vs. Active-matrix

• Resolution limitations

• Considerably more expensive than CRTs

image courtesy of Viewsonic.com

Flat-panel Plasma Displays

• Brighter than LCD

• Easier to manufacture (theoretically)

• Mainly used for large-scale applications

image courtesy of Viewsonic.com