Module 2 – Using the Computer and Managing Files
Utilities
File Compression
In computer science and information theory, data compression is the process of encoding information using fewer
bits than an unencoded representation would use through use of specific encoding schemes. For example, the ZIP
file format, which provides compression, also acts as an archiver, storing many source files in a single destination
output file.
As with any communication, compressed data communication only works when both the sender and receiver of the
information understand the encoding scheme. For example, this text makes sense only if the receiver understands
that it is intended to be interpreted as characters representing the English language. Similarly, compressed data
can only be understood if the decoding method is known by the receiver.
Compression is useful because it helps reduce the consumption of expensive resources, such as hard disk space or
transmission bandwidth. On the downside, compressed data must be decompressed to be used, and this extra
processing may be detrimental to some applications. For instance, a compression scheme for video may require
expensive hardware for the video to be decompressed fast enough to be viewed as it's being decompressed (the
option of decompressing the video in full before watching it may be inconvenient, and requires storage space for
the decompressed video). The design of data compression schemes therefore involves trade-offs among various
factors, including the degree of compression, the amount of distortion introduced (if using a lossy compression
scheme), and the computational resources required to compress and uncompress the data.
( Source: http://en.wikipedia.org/wiki/Data_compression )
1. Define the following words in relation to the above article;
Compression
Data compression is the process of encoding information using fewer bits than an unencoded
representation would use through use of specific encoding schemes
Decompression
Data decompression is the process of decoding compressed data back to it’s original state
Encoding
Encoding is the process of transforming information from one format into another
Decoding
Opposite of encoding
CODEC
COMpression / DECompression - is a device or program capable of encoding and/or decoding a digital
data stream or signal
Algorithm
A set of instructions / mathematical steps used to produce an encoding/decoding method
Archive
Is an organized collection of files / data, normally stored in one compressed file
2. Name three pieces of software which provide file compression/decompression and archiving features
WinZip
WinRAR
Stuffit ( Mac )
3. MP3 ( Mpeg 1, Audio Layer 3 ) is a is a digital audio encoding format using a form of lossy data
compression.
Why is this method termed as “lossy”?
Because sound quality is lost when the music file ( normally a .wav or .cda file ) is compressed/encoded.
Higher compression leads to lower bitrates and the introduction of mp3 artefacts
What would be the difference between an mp3 music file with a bitrate of 32kbit/sec compared to one
with a bitrate of 320 kbit/sec?
32kbit/sec is the highest compression and the quality would only be suitable for voice files. 320 kbit/sec is
uncompressed and the quality/filesize would be the same as the original. 128kbit/sec is considered “near
CD” quality resulting in about 1Mb of storage space per 1 minute of music file
4. Explain what is meant by a Computer Virus
A computer virus is a computer program that can copy itself and infect a computer without permission or
knowledge of the user. A virus can only spread from one computer to another when its host is taken to the
uninfected computer
5. Give three typical ways that a computer virus might infect a personal computer
Network / Internet / Removable Storage Medium / Email / Instant Messaging / File Sharing, etc.
6. What are the two main differences between a computer virus and computer worm?
A worm can spread itself to other computers without needing to be transferred as part of a host
Worms may cause harm to either a computer system's hosted data, functional performance, or networking
throughput, when executed. In general, a worm does not actually harm either the system's hardware or
software
7. Why does anti-virus software need to be updated regularly?
Because the list of virus “signatures” changes on a daily basis
8. What is meant by heuristic scanning and how might this help to protect a computer without the most
recent virus updates?
“Heuristics” simply explained means “Learning by Experience”. Using a heuristic algorithm to find viruses
means the solution is based by analysing common behaviors of known viruses. This method has the ability
to detect viruses that anti-virus security firms have yet to create a signature for.
9. Give two methods other than use of anti-virus software that would help reduce the effect of a virus attack
Make regular backups of data
Use different operating systems and different filesystems