Storage

1
Storage
CHAPTER 4
Objectives

• Discuss the various types of media storage.
• Understand the characteristic of the hard disk
  floppy disk.
• Understand how the data is stored, fragmentation
  defragmentation.
• Differentiate among CD-ROM, CD-RW, DVDs

2

• Storage holds data, instructions and information
  for future use. Inside your computer there are
  two types of data storage
• Permanent - stay in the system even when the
  computer's power is turned off.
• Temporary - when the system is turned off, data
  in temporary storage disappear.

3
What is storage?

• Holds data, instructions, and information for
  future use

• Storage medium is physical material used for
  storage

• Also called secondary storage

4
4.1 Criteria for rating secondary storage

• Storage capacity / size
• High capacity storage devices are required for
  many sophisticated programs and large databases.
• Speed
• People prefer whichever that is fast, but the
  problem is, it will cost more. The fastest
  storage is RAM ? Hard Disk ? CD ?Zip Drive,
  Floppy and Magnetic Tape. The speed is usually
  measured by access time.
• Access time
• Refers to the average time needed to locate data
  on the medium. Measured in ms for secondary
  storage, ns for RAM.
• Cost
• The faster the storage device , the more
  expensive it is. RAM ? Hard Disk, CD, Zip Drive,
  Floppy and Magnetic Tape.

5
4.2 Magnetic Disk Storage

• Based on the technology of representing data as
  magnetized spots on the disk.
• With a magnetized spot ?1 bit and without such
  spot ? 0 bit.
• To open a file means
• read data from the disk by converting the
  magnetized data to electrical impulses that are
  sent to the processor.
• Saving means
• writing data to disk by sending electrical
  impulses from the processor to be converted to
  magnetized spots on the disk.

6
4.2.1 Diskettes

• A removable round, flat piece of Mylar plastic
  that stores data and programs as magnetized
  spots.
• Sizes of diskettes
• 3 ½-inches

7
4.2.1 Diskettes

• Disk drive - device that holds, spins and reads
  data from and writes data to a diskette.
• A diskette is inserted into a slot, called the
  drive gate or drive door.

8
(No Transcript)
9
(No Transcript)
10
4.2.2 Hard Disks

• What is a hard disk?
• High-capacity storage
• Consists of several inflexible, circular platters
  that store items electronically
• Components enclosed in airtight, sealed case for
  protection

11
4.2.2 Hard Disks
11
12
4.2.2 Hard Disks

• What is a head crash?
• Occurs when read/write head touches platter
  surface
• Spinning creates cushion of air that floats
  read/write head above platter
• Clearance between head and platter is
• approximately two-millionths of an inch
• A smoke particle, dust particle, or human hair
• could render drive unusable

12
13
(No Transcript)
14
(No Transcript)
15
4.2.2.1 The Roles That DOS Plays
A typical floppy disk stores data on both sides.
It has 80 tracks on each side and 18 sectors per
tracks. Calculate the capacity of the floppy disk
.
16

• What are tracks and sectors?

16
17

• DOS keeps track of the various portions of a file
  with a device called a File Allocation Table
  (FAT).
• The FAT is a directory of sectors it serves as a
  guide in locating all the clusters in which
  portions of a file are stored.

• Formatting prepare a track on floppy so that
  the operating system can write information on it.
  
• The most common reasons to format a hard disk
  are 1) The drive has contracted a virus that
  cannot be removed without destroying the
  boot sector. 2) The drive is developing bad
  sectors.
• 3) You are changing from one operating system
  to another and wish to remove everything from
  the drive.
• Write-protect features - protect a diskette from
  being written to.

18
Sectors and Clusters
19
4.2.2.2 How data is organized on a disk
20
3 - Cylinder method

•                                                 
                                                   
  
• The organizational is vertical to reduce the time
  it takes to move the access arms of a disk pack
  into position. Once the access arms are in
  position, they are in the same vertical position
  on all disk surfaces.
• Tracks within a cylinder are numbered according
  to this vertical perspective.

21
4.2.2.3 Fragmentation and Defragmentation
Defragment your own pc Start gt program files gt
accessories gt system tools gt disk defragmenter
22
4.3 Optical Disk Storage

• Is a removable disk on which data is written and
  read through the use of laser beams.
• A high-power laser beam is used to represent data
  by burning tiny pits into the surface of a
  hard-plastic disk.
• To read data, a low-powered laser light scans the
  disk surface
• Pitted areas are not reflected ?0 bits
• Smooth areas ?1 bits.
• Main types of optical storage are CD-ROM, CD-R,
  CD-RW and DVD.

• CD-ROM (compact discread only memory)
• Is an optical-disk format where the content is
  recorded at the time of manufacture and can only
  be read. Capacity is up to 660 megabytes per
  disk.

23
4.3 Optical Disk Storage
Step 2.If light strikesa pit, it scatters. If
light strikes a land, it is reflected back toward
diode.
Step 1.Laser diode shines a light beam
towarddisc.
23
24

• CD-R (compact disc - recordable)
• Permits writing on optical disk where CD-R drive,
  CD-R disks and accompanying software are
  required. Once written, data can't be modified
• CD-RW (rewritable)
• Erasable disc allows you write on it multiple
  times. To write on CD-RW, you must use CD-RW
  drive
• DVD-ROM (Digital video disc-ROM)
• Looks like an audio compact disk but can store
  4.7 to 17 GB, allowing great data storage,
  studio-quality video images, and theater-like
  surround sound.

25
4.3 Optical Disk Storage
single trackspirals to edgeof disc

• How is data stored on an optical disc?
• Typically stored in single track
• Track divided into evenly sized sectors that
  store items

disc sectors
25
26
4.4 Magnetic Tape Storage

• One of the first storage used with mainframe
  computer.
• It's a thin plastic tape that has been coated
  with substance that can be magnetized
• Mainly used for backup
• not used for primary method of
• storage because it is a sequential-
• access media (slow to access data)

27
4.4 Magnetic Tape Storage

• How is data stored on a tape?
• Sequential access
• Reads and writes data consecutively, like music
  tape
• Random access
• Used on hard disks, CDs, and DVDs which can
  locate particular item immediately

11/10/2009
27
28
4.5 PC Cards

• PC Card is a thin, credit-card-sized device that
  fits into a PC Card slot and is commonly used in
  notebook computers.

4.6 Miniature Mobile Storage

• Allow mobile users easily to transport digital
  images, music or documents to and from computers
  and other devices. E.g USB Flash Drive, Smart
  Card .

4.7 Microfilm and Microfiche

• Store microscopic images of documents on roll or
  sheet film.

29
4.8 Online Storage

• What is online storage?
• Service on Web that provides storage for minimal
  monthly fee
• Files can be accessed from any computer with Web
  access
• Large files can be downloaded instantaneously
• Others can be authorized to access your data

29
30
Tutorial 1. Given the size of a movie is 20 GB
and the capacity of a backup storage X is 2MB.
Calculate how many X are needed to copy the whole
movie ? 2. The capacity of a floppy is defined
as 1.38MB . Calculate how many floppies are
required to copy all the data from a 2GB DVD. 3.
Which one is cheaper ? 20GB of Hard disk for
RM220 or 1TB of Hard disk for RM 11 000 . Prove
it.