3.1.3 Information Coding Schemes

ASCII

ASCII is a form of coding language that started to be created in the late 1960's. This coding language was created to represent text in computer, communications equipment and other devices that use text. ASCII stands for America Standard Code for Information Interchange. here is an example of a ASCII table;

ASCII uses 8 bit coding to represent each of the characters.


















Unicode


Unicode is another different coding language, but unlike ASCII, unicode uses 16 bit. This is enough  for all the character used in every language in the world, including technical and mathematical symbols in the world.


Some of the different tables are here; http://www.unicode.org/charts/ be sure to check this!! To know what the tables look like etc.


Error Checking


There are a few different error checking systems;

Parity Bit error checking

A parity bit is a bit that is added to a group of source bits to ensure that the number of set bits (i.e., bits with value 1) in the outcome is even or odd. It is a very simple scheme that can be used to detect single or any other odd number (i.e., three, five, etc.) of errors in the output. An even number of flipped bits will make the parity bit appear correct even though the data is erroneous.


The majority vote method


Send the data three times
Use the most common value for each bit as the received value:
E.g we try to transmit: 01100110
So we send


01100110
01000110
01101110

3.1.4 Systems development lifecycle

Following s structured lifecycle can reduce the risk of projects failing. When projects fail....at best the is a lot of money, at worst people loose their lives.

There are 5 phases of the lifecycle;

Analysis
Why???
- new business opportunities
- new laws
- mergers
- new technology etc.

Design
The design phase is used to create a specification for a system that will meet the need identified in the analysis

Included is;
- hardware
- software
- data
- buildings?
implementation
- build the system
- hw racking
- sw install
- data migration
- training
- documentation

Testing
- verify (have we built the thing right)
- test part on their own
- test the whole
- test the people!

Evaluation

Used for:
- validate (have we built the right thing)
- check it's effectiveness
- identify future work

After
O maintenance, where we;
- fix/detect problems
- adapt the system over time
- add new features
- can cause the whole cycle to be used again for big changes.

3.1.1 Finite state machines

Finite State machine (FSM)


A FSM is a machine (physical or computer program) that consists of a fixed set of states. The FSM has a set of allowable inputs that change the state. The FSM has a set of possible outputs which depend on the current state (and thus the history of inputs which led to the current state)


Finite state automation (FSA)


A FSM with no outputs is called a finite state automation.


State Transition Diagrams
Are there to represent an FSM

State Transition Tables
Are there to represent an FSM

Decision Tables


Decision tables are a very useful tool when you are designing/testing algorithm. They let you map out all the possible combinations and what should happen..so that you can check you have handled them in the code.

Different notations

3.1.3 representing sound

Analogue


Analogue data varies continuously (all values are possible), think about how an analog clocks hands sweep every place on the clock face.


Digital


Digital data varies in discrete steps(only certain fixed values as possible)
Signal

Analogue to Digital (ADC)

•First, the continuous (analogue) sound signal is sampled at regular intervals. This is called Pulse

Amplitude Modulation (PAM)

• Each value is then rounded down to an approximate value dawn from a range of possible

discrete (digital) values.

•The value is then stored as a binary digit

•The technical term for approximating a sound sample to the closest digital value is

quantization

•Each quantized number represents a Pulse Code Modulation (PCM)

•Each individual PCM (binary number representing one sample from the sound) is stored in

sequence in a file to record the sound in a digital, binary file

Sampling


there are two factors that affect sound quality

• Sound rate - how many times per second a sample is taken.
• Sampling resolution the number of bits available to encode each sample

Sound files


- WAV : 1 min = 2.5mb
- MPEG (used in .mp2, .mp3, .mp4)
discards frequencies that the ear/brain cannot handle


which make the file about 10% of the original
1min = 0.25mb


Streaming audio


-The server sends the sound bit by bit
- The client buffers it and plays it when it has enough to keep going whilst buffering more


Advantages
- no need to download the file - just start playing
- saves hard drive space
- makes copying harder


Disadvantages
-cannot listen when not connected
- affected by bandwidth


Nyquist's theorem


frequency is measured in Hz (KHz, MHz)
Nyquist's theorem states that: "we must sample at a frequency at least twice the rate of the highest frequency in the signal"

3.1.3 representing images

 Bitmaps
A bitmap image is a spatially mapped array of bits. It is simply a file holding an array of 1s and 0s which when arranged create a shape, (eg a square) forms an images.

Vectors
vector graphics are much, much smaller in file size and do not suffer from this scaling problem. This is how they achieve it;
instead of storing the image as a set of pixels they store the instructions (genetic info and properties) needed to recreate the image
eg. rect(0,0,2700,2700,black,filled,none)


The advantages

• Smooth scaling 
• Smaller files
• load faster from storage

Compression
There are two methods of compression;

first options with out losing any information - run length encoding (RLE) replaces continuous blocks with just the colours and numbers of the blocks

second option throwing away some information - remove bits we find hard to see/wont notice (JPEG)
                                                                 - every time you save a JPEG again as a JPEG you lose more info

consequences of uses of computer

The computer misuse act 1990
exists to protect against unauthorized use of computer systems.
There are three levels of security:
1. unauthorized access to data and/or programs
2. unauthorized access with intent to omit a further offence
3. unauthorized modification of computer material


Data protection act 1984 and 1998
There are 8 key principles to the data protection act:
1. data gathering - do they know im collecting it?
2.data purpose - do i know an exact reason for collecting it?
3.data quantity - am i sure the data is no more than is needed?
4.data quality -  am i keeping accurate and up to date data?
5. data lifetime - do i really need to keep this data anymore?
6.data subject - can they be told what data i am holding?
7. internal data security - have i put in place sufficient security?
8. external data security - am i moving data to a country which does not have the same level of protection?


Regulation of investigatory powers act 2000 (RIPA)

• prevents the interception of public and private messages
• allows security and intelligence services to intercept
• can be used to force ISP's to help
• only applies to a message that is moving

Copyright, designs and patents act 1988

• copyright protects materials like art, music, sound recording and films
• Design rights protects somethings looks
• Patents protect how an innovation works or what it does
• Trademarks protect the name or logo of a business

Health and safety (display screen equipment)
obliges employers to look after (provide training and information) for staff who use computers for extended periods

Digital Right management
is an application of controls to limit to use of digital media, used by the copyright holder to try and limit when you can use digital media


Robotics 
robotics is a huge factor in daily life at the moment and there are many strengths and weaknesses that come with it; they are extremely versatile and very efficient but cannot make complex emotional or social decisions. they are used in various different areas including; deep sea diving, manufacturing and bomb disposal.




Code of conduct
sets out how an organisation expects you to use its computers and behave when on them

What are the basic internal components of a computer system?

3 box model

Processor


The processor is the brain in the system. It is responsible for executing programs and supervising the functioning of the other parts of the system. The processor is perhaps the most complex element in the system.


Main Memory

Main memory can be split into two categories;

RAM


Or random access memory is used for memory that is readable and writable. It can be implemented in many technologies. RAM is used by the processor to store (write) data and load (read) it back. The contents of RAM is volatile - they are forgotten when the power is turned off
 
ROM

Read-only memory (ROM) doesn't forget when the power is turned off - the content is not volatile. ROM provides random access like RAM but it cannot be written to once it is set up. It is used to hold fixed programs such as the bootstrap program in a PC.

I/O


To be useful, the CPU needs to communicate with devices known as peripherals. 

I/O controller: allows the computer to communicate with peripherals without the CPU knowing how they work.

I/O Ports: its a method of performing inputs and outputs between CPU and peripheral devices in a computer.

Bus

Address
a unidirectional bus, typically consisting of 32 wires, used to address memory and I/O locations
Data
a bidirectional bus, typically consisting of 32 wires, used to transport data between the three components of the three box model
Control
a bidirectional bus, typically consisting of 8 wires, used to transport control signals between the three components of the three box model