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Computer Applications-COB2

Computer Applications - CPA
by

Annie Clare Lee

on 24 June 2010

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Transcript of Computer Applications-COB2

Devices How
storage media
work Units
to measure
Data Dealing with Large files Back-ups It is different from back ups. What is a Storage media? Is a representation of information in a manner suitable for computers
Is meaningless on its own
Becomes information when interpreted
Data A form of material
Used to store data Storage medium Storage enables computers to Store information
Retrieve information for later use Different Storage Media Zip disk
250 MB Memory Card/
USB flash card
32 MB - 100 GB Diskette
1.44 MB Hard Disk
10 - 200 GB CD- ROM
650 MB DVD
4.7 GB Most common form of storage:
Magnetic
Optical
Computers store data in 1s and 0s
These are binary numbers. Magnetic storage
Has a layer of many tiny magnets
1s and 0s represented by the directions magnets are pointing
Directions of magnets can be changed can erase and add data
Smallest unit of data is the bit
Can store two values: 0 and 1
Next level unit of data is the byte

Consists of 8 bits
A character (e.g. A, B, C, a, b, c, 1, 2, 3, $, …) is represented by 8 bits 1 kilobyte = 1,024 bytes
1 kilobyte is written as 1 kB

1 kB = 1 kilobyte = 1,024 bytes = 1,024 x 8 bits
1 kb = 1 kilobit = 1,024 bits

1 megabyte = 1,024 kilobytes
1 gigabyte = 1,024 megabytes
What is considered a large file?
Depends on the context
Capacity of commonly used storage media
Data transmission speed
The more data a document contains, the larger the file
File compression A technique to make a file smaller
While preserving all its data Popular file compression programs WinZip
WinRar File compression is possible because most files contain empty space Another reason why files can be compressed is that
Files can only be saved in fixed sizes. However, you need to decompress to use the file before you can use it
Decompressing a file will slow down your computer if you use the file frequently Compressing a file saves space Memory Management Memory is used to
Store data
Pass data around

Computer has limited memory because memory is expensive
Supplied with “just enough” memory
What is “just enough” depends on the memory requirements of the programs
Because memory is limited,
how it is managed is important
What happens when a PC is short of memory? allocates less memory to applications
prevents applications from running
borrows memory from slower running storage devices such as the hard disk Back up is
Copy files to another medium (a disk or tape)
For possible recovery
In case the first medium fails and the originals are lost.
Data loss due to virus infection
Restore uninfected backed up data files

However, it may take weeks for viruses to appear.
Hence,
Keep normal back-up for at least a few weeks so you can restore computer to uninfected state. To create and maintain a reliable back-up system, you need to determine:
What data needs to be protected
What media to use
How to protect the media
Establishing a Back-up Plan Schedule back-ups
Frequency of back-ups depends on
Importance of data
How quickly data changes To ensure backed-up data can be restored
This is important as storage media can deteriorate with time Test backed-up data regularly Getting a new storage device! Factors to consider
Reliability
Speed
Capacity
Cost
Compatibility with your OS
Most back-up systems allow you to back up on removable storage




Types of storage media
Match capacity of storage media with quantity of data to back up
Reasons
Preserve older backup versions
Faulty storage media
Longer life span of storage media
Rotate your back-up media! Archives Good performance
High media capacity
Good read/write speed
Lowest cost possible

The magnetic tape is commonly used
Meets the performance and cost criteria
Reasons for Back-up Requirements
Reasons for Achive Requirements Archives may be recalled after years
Media’s longevity and data authenticity are very important

The storage media needs to have a stable and long life
Otherwise need to change media frequently

Archives optimise data by removing seldom used historical data
Improves system performance
Archives need to be accessible

Archives are sometimes used as evidence
Must be protected from modification

Archives need to provide fast information retrieval

The total cost of ownership for archives must be considered
(Cont'd)
Reasons for Achive Requirements Hard disks
Best performance
Highest capacity
Relatively short lifespan of several years
DVDs
Long life
Reasonably priced
Low capacity (9.4 GB)
Average performance
Archival Storage Technologies
MOs (Magneto-Optical storage)
Old-generation disks that have a storage capacity of 9.1 GB
Superseded by UDOs which can store 30 GB
Record only once
Fast random access
Long media lifetime. (Cont’d)
Archival Storage Technologies Archives secure historical data; back-ups secure current data
Consistent back-ups ensure that data can be recovered in the event of a disaster
Archives improve performance of back-ups by removing historical data so that there will be less data to back-up
Archives and back-ups complement each other
Full transcript