A-level Computing/Print version
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A-level Computing is an A-level course run for students in the UK
Note: current version of this book can be found at http://en.wikibooks.org/wiki/A-level_Computing
Table of contents
Introduction
AS modules
- Computer Systems, Programming and Network Concepts
- Principles of Hardware, Software and Applications
- Practical Systems Development (Short practical project)
A2 modules
Answers
Authors
Contributors
- Mr. P. Kemp - East London
- Mr. A. McPherson - West London
- Mr. J. Edwards - Isle of Man
Thanks for helping out!
License
GNU Free Documentation License
Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
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Overview
Introduction
This is a book about A-Level Computing. It aims to fit in with the AQA GCE A-Level Computing syllabus but is not endorsed by AQA. It should be useful as a revision guide or to find alternative explanations to the ones in your textbook. If you haven't heard of an A-Level then this book probably won't be of much interest to you but you can find out about them at Wikipedia.
If any part of this book is unclear or even wrong then please post a comment on the discussion page or simply fix it yourself! In particular, please say if the book assumes any knowledge or skills which not all A-Level Computing students have.
Course Structure
- To be awarded an AS (Advanced Subsidiary) Level qualification in Computing, a student must take the 3 AS modules.
- To be awarded an A (Advanced) Level qualification in Computing, a student must take all 6 modules.
Modules
Please note all modules have complementary question and answer sections
AS modules
- Computer Systems, Programming and Network Concepts
(Sep 24, 2006) - Principles of Hardware, Software and Applications
- Practical Systems Development (Short practical project)
A2 modules
- Processing and Programming Techniques (June 18, 2006)
- Advanced Systems Development
- The Practical Project
Appendix
- ICT Projects using LAMP
- A2 Computing Projects using Microsoft Visual Web Developer Express Edition
- Exam Tips
- Authors
Computer Systems, Programming and Network Concepts
This is the Computer Systems, Programming and Network Concepts module of the A-level Computing Book. This module consists of four chapters listed below with their short summaries. Please follow the links to learn out more about each section.
Contents
- Introduction to Computer Systems
(Sep 24, 2006)
An introduction to the hardware components of a computer system and the different types of software. Overview of the interaction between software and hardware, binary notation in computers and execution of the processor. - Introduction to Programming
(Sep 25, 2006) - Introduction to Information and Data Representation (Sep 26, 2006)
- Introduction to Communication and Networking
Introduction to Computer Systems
Definition of this section is available at [1], page 16. This text will be expanded shortly
What is Hardware and Software?
At the highest level, a computer system is composed of hardware and software components. Hardware consists of all the physical devices. All the programs (code) that run on the computer system form the software part. The hardware and software are tightly coupled and they complement each other. Hardware is useless without software and software requires hardware to carry out computations.
Different Types of Software
System Software
System software is anything that is an essential part of the computer system; or in other words a software is the artificial intelligence which dictate the rules of operation within its systems.
Operating system software
An operating system is the low-level software that acts as an interface between the user and the hardware. The OS provides a "virtual machine" where the user is safe to execute their applications and program code.
Common operating systems include Microsoft Windows, Mac OS X and GNU/Linux derivatives.
Utility programs
Utility software helps manage and tune the computer hardware, OS or application software. It usually performs a single task or small range of tasks. Good examples include:
- Archive: utilities take a file or collection of files and output a single file or stream.
- Disk defragmenters: reorganise file structure so that all file fragments are contiguous on the disk. Modern filesystems, such as those used by Mac OS X and GNU/Linux, do not need explicit defragmenting.
- Encryption: utilities use a specific algorithm to encrypt/decrypt the contents of a file or stream using an encryption key.
- Virus scanners: scan for malicious computer program code in files.
Library programs
A collection of subprograms used to develop software and hardware compatibilities. Libraries contain "helper" code and data for other programs to use in a modular way; they are usually not executable and exist purely to provide services to other programs.
Compilers, assemblers and interpreters
A compiler is a computer program that translates code written in a high level language to a lower level language, e.g. assembly language or machine language. The most common reason for translating source code is to create an executable program (converting from a high level language into machine language).
Advantages of using a compiler
- Source code cannot be stolen/copied
- Tends to be faster than interpreting source code
- Produces an executable file, and therefore the program can be run without need of the source code
Disadvantages of using a compiler
- Object code needs to be produced before a final executable file
- The source code must be 100% correct for the executable file to be produced
An assembler translates assembly language into machine language. Assembly language consists of mnemonics for machine opcodes so assemblers perform a 1:1 translation from mnemonic to a direct instruction. Conversely, one instruction in a high level language will translate to one or more instructions at machine level.
Advantages of using an assembler
- Assembly code is often very efficient (and therefore fast) because it is a low level language
- It is fairly easy to understand due to the use of English-like mnemonics
Disadvantages of using an assembler
- Lots of assembly code is needed to do relatively simple tasks, and complex programs require lots of programming time
- Assembly tends to be optimised for the hardware it's designed for, meaning it is often incompatible with different hardware
An interpreter program executes other programs directly, running through program code and executing it line-by-line. This is slower than running compiled code but it can take less time to interpret program code than to compile in then run it — this is very useful when prototyping and testing code.
Advantages of using an interpreter
- Useful for prototyping software and testing basic program logic
- Easy to find errors in source code because the translation will stop when an error is encountered
Disadvantages of using an interpreter
- Source code is required for the program to be executed
- Interpreters are generally slower than compiled programs due to the per-line translation method
Application Software
Application software is designed for the user to allow them to solve a task. These may include Word processors, spreadsheets and database packages. (NOTE: do not use brand names in the exam, unless asked to, it is better to use the type of software instead, e.g. Excel Spreadsheet package)
General purpose
General purpose application software is designed to solve a wide range of tasks, for example:
- Word processor
- Spreadsheet package
- Presentation package
Special purpose
Special purpose application software performs a specific task or set of tasks, for example:
- Media player
- Accounting
- Vector drawing
Bespoke
Bespoke application software has been written specifically for the needs of a user or company. It is "tailored" to their exact requirements. Some examples might be:
- Air traffic control
- Factory robot
- Tourist kiosk
Introduction to how computers store data
Computers can't understand colours, words and sounds like humans. Even if you use digital cameras and voice recognition, a computer has to translate these inputs into the only language it does understand, that is the language of 1 and 0. This is called binary.
Binary is different from our own decimal numbering system. Instead of having 10 different values like decimals: 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 (this can also be referred to as denary or base 10), binary (or base 2) only has 2 values: 0 and 1. A binary digit, or bit as it is more commonly known, can either be set to 0 (off) or 1 (on).
By combining many bits together, we create what are known as "bit patterns". Inside the computer, all data is transmitted and manipulated in bit patterns. Apart from individual bits, the two other most important bit patterns are:
- Byte: This is a series of eight bits that computers tend to use as the smallest number of bits to store data, e.g. 10110110.
- Word: This is sometimes called a 'manipulation unit'. It is a set length of bits that varies between types of computers, but is usually 32 or 64 bits long in most modern computers.
- Program: A program is a set of instructions that are processed by the computer to do a specific operation. This could be anything, from adding two numbers and outputting the result, to the complex instructions in the program of a computer game.
- Data: Data (the singular is datum) are raw numbers that have no meaning by themselves. Data could be stored about parts of a video clip, an image, a sound, text or a number.
What parts make up a computer?
These components are found in virtually every computer:
- Processor: The 'brain' of the computer. It executes instructions sequentially and processes data. The processor is usually divided up into the Arithmetic and Logic Unit (ALU), and the Control Unit. The ALU carries out logical evaluations (for example comparisons), and mathematical expressions (such as addition and subtraction). The Control Unit carries out the functions that organise instructions and co-ordinates all the data and instructions, similar to traffic lights controlling the flow of cars. The processor is also called a Central Processing Unit (CPU).
- Clock: A piece of hardware used to keep the processor (and some other integrated circuits) in time by oscillating at a steady frequency.
- Main Memory: This is temporary storage that stores data currently being worked on. It is accessible to the processor directly, without going through any input/output channels. It does, however, need to connect to the processor via the data, address, and control buses. When power is lost, all data stored in main memory is lost, therefore meaning it is volatile. Main memory is also known as Immediate Access Storage (IAS).
- Address Bus: A collection of wires between the processor and main memory used to communicate the physical location (address) of data in main memory.
- Data Bus: A collection of wires between the processor and all internal devices, and is used to send and receive both data and instructions.
- Control Bus: A collection of wires between the processor and devices used to send commands and get status signals from the devices. For example, it could show whether the computer was reading or writing to memory.
- I/O Port: An interface and physical connector that allows peripherals, such as a keyboard, mouse or monitor, to communicate with the 'heart' of the computer system — the processor and main memory. I/O stands for Input/Output.
- Secondary Storage: This is computer memory that is not directly accessible to the processor but uses the I/O channels. It is for storing data not in active use and preserves data even without power, meaning it is non-volatile.
diagram is needed here
How to run programs
All programs are stored as a series of bit patterns ready to be executed (or "run") by the processor. All modern computer systems use the "stored program concept". This is where program instructions are loaded into main memory for the fetch and execute cycle.
The stored program concept basically states that both instructions and data to be operated on can be loaded into memory at the same time, as opposed to having the instructions pre-programmed into the hardware, and then passing this hardware the data to be processed.
The fetch-execute cycle is the retrieval of data and instructions from main memory through the data bus, and then executing the data or instructions using the processor.
An example of these ideas working together would be when a computer system was required to add two numbers together. A program that adds numbers is loaded into main memory. Then each instruction of the program is fetched and executed one after the other by the processor, along with any data required (in this case the numbers to be added). The processor stores the current instruction in a special register and uses its Arithmetic and Logic Unit to process the instruction.
Introduction to Programming
What is Programming?
Programming is the ability to get a computer to perform tasks by writing instructions that a computer can understand and execute. You must remember that the only language a computer understands is binary, a combination of 1s and 0s. This section looks at how we can write instructions and get the computer to understand those instructions.
Programming Languages
When computers were first developed in the 1940s the only way to send instructions to them was by sending them 1s and 0s through flick switches and buttons. Even though the process of sending a computer instructions got better evolving through punch cards, paper tape, magnetic tape and disks, the language computers understand has not changed from the pattern of 1s and 0s, machine code. However the way humans construct these 1s and 0s has gotten easier.
Levels of Programming Language
High/Low level programming languages are terms used to describe how abstracted the language is from the raw machine code and hardware manipulation. Whether a language is high or low level is purely subjective towards the comparison made. Assembly is considered a low level language but is a higher level langauge than machine code as it resembles English more closely. B.A.S.I.C is even further abstracted and can thus be considered a high level language.
Machine Language - First Generation
The 1s and 0s that a computer can understand and execute
100100101110101000101011010010100101
It is very difficult for humans to understand and difficult to write unaided. Machine code tends to be produced for a specific hardware set up and thus it is not portable to different machines.
Low Level Language - Second Generation
In a low level language the programmer controls and specifies the specifics of how to handle the data, where to store it, how to access it and so on. Assembly is said to be a low level language. Here is a source extract to print "Hello World!" to the screen
; This program displays "Hello, World!"
dosseg
.model small
.stack 100h
.data
hello_message db 'Hello, World!',0dh,0ah,' '
.code
main proc
mov ax,@data
mov ds,ax
mov ah,9
mov dx,offset hello_message
int 21h
mov ax,4C00h
int 21h
main endp
end main
 |
easier to write and understand when compared to machine code |
|
allows low level access to hardware features |
|
can produce small program sizes |
|
can produce very fast code |
 |
not as easy to understand and write when compared to high level language |
|
may be written specifically for a certain hardware set up and will therefore not be portable |
High Level Language - Third Generation
A high level programmming language is one in which the specifics of data handling and manipulation is abstracted away (more so than in a low level language). A high level language generally has more built in functionality than a lower level language and is closer to English for a person to understand. C++ is considered a high language. Here is the source to print "Hello World!".
#include <iostream.h>
using namespace std;
int main()
{
cout << "Hello World!";
return 0;
}
//Note: This code may or may not be compilable, as it varies between compilers and platforms.
|
easy to write and understand |
|
built in libraries to perform routine tasks |
|
can be ported to multiple hardware setups from same code |
|
may be slower than second generation languages |
|
may produce larger program files for same functionality than second generation langauge |
|
may not allow for low level hardware access |
Program Translators
We already know that computers can only execute Machine Code, so we need a way to convert from 2nd and 3rd generation languages to 1st generation, machine code.
There are three different methods that you may have to use. Assemblers, Compilers and Interpreters
Assemblers
When using Assembly language you will have to use an Assembler. The Assembler will take the assembly code and convert it into the correponding Machine Code 1s and 0s (actually current flowing and current off). There is a one to one correspondence between a single assembly language instruction and a machine code instruction. In general there will be one line of Machine code produced per line of assembly language. This translation or conversion is called 'assembling' and is performed by a piece of software called an assembler before execution of the code can take place.
Compilers
When using a high level language you will have to use a compiler to turn your code into the corresponding machine code. This is done using a compiler and performed before the execution of the code. A program like a Playstation computer game will be written in a High level language and compiled into machine code. This code will then be burnt to disk at the factory and sent to the shops, when you buy it and place it in the DVD drive of the PS2, the processor will execute the machine code.
Interpreters
Another way of running code written in High level languages is to use an interpreter. This will convert the code you write in machine code for the processor to execute. However the difference here is that the code is converted into machine code as you are running the program, so the code is interpreted only when you need to run it, line by line. This can be much slower than compilation but allows for you to correct errors in the code (debugging) when you meet them. It is also used in common languages like Java and allows you to run the same code on multiple hardware set ups as long as you have an interpreter for that hardware. Think along the lines of running the same Java Application on Linux, Windows and your mobile phone.
Comparisons
You may be asked in the exam which translator you would recommend, here are a few things to think about
- If the code is in Assembly Language (2nd Generation), then you will use an Assembler
- If you want the fastest code you will use a compiler
- If you want the code to be able to run on multiple machines you will need an Interpreter
- If you want to debug code and not have to recompile with every change you make, you want to pick an Interpreter
Programming Concepts
In this module we will be looking at Imperative languages, Imperative languages are languages that execute one line after another, take this example for instance
int x = 1; x=x+1; x=x+1; x=x+1; cout << "x = " << x; // print x
output:
x = 4
Declaring a variable then assigning a value to that variable is called Assignment
int x; x = 45; // this is assigning the value 45 to the variable x
There are other sorts of languages that you will meet in module 4, but for the moment you only need to know about imperative languages. You will not need to know a particular language for the exam but knowing the concepts behind them and how to understand the pseudo code is essential - pseudo code is close to a third generation language, which is understandable what it should do to you and me, but probably wouldn't run on a computer. This section will now outline a few of the concepts you need to understand
Type Definitions
You may have met datatypes in GCSE when using databases or spreadsheets. The idea behind them is to use a type of data to store information that best matches the data you want to store. In computers this is incredibly important as you are trying to make the best use of the computing resources available, so picking the data type that matches the information you are declaring will be the most efficient way of storing the data. For example if you want to store a number you don't want to use a data type that can also store letters and other characters as this would be a waste of space. e.g.
3 stored in ASCII is 0010 0011 3 stored in pure binary is 0011, thus saving 4 bits
In any programming language you generally have 4 different data types.
- Integers
- Integers are whole positive numbers, but unlike in maths the integer range will have limitations to the maximum number. The limitations can vary greatly.
- e.g. 104
int x = 45; //declares an integer called x and sets the value to 45
- Strings (Characters)
- Strings are a collection of single block characters. e.g.
- e.g. as54sfgjf/.dfg4
string x = "herman";
- Booleans
- Booleans are variables that are like on/off switches and generally can only equal two values.
- e.g. TRUE/FALSE ON/OFF 1/0
bool x = TRUE;
- Pointers
- Pointers are an advanced variable type. A Pointer is a 32bit or 16bit or 64bit number (depending on the environment), this number represents a single block in your computer memory. In essence it points to this memory block because you know that it is th nth memory block. Pointers are probably the most useful variable type however you may or may not come accross them depending on what language you are using and how high/low level it is. You do not need to know about pointers for module 1.
There are also other datatypes that languages may possess, such as:
- Character
- The Character data type is a single character.
- e.g. g
char x = 'g';
- Real
- Real is a more advanced number system than integer, allowing for rational and irrational numbers, decimal places and negatives
- e.g. -12.3231
real x = -23.432;
- Array
- Arrays are collections of other datatypes, generally able to store only one datatype, for example an array of type string may look like this:
- (red, green, orange, blue, brown)
array x = new array ("red", "green", "orange", "blue", "brown")// declare array with five elements, each of type string.
-
- Think of an array as a spreadsheet; you have the array (x), which is like a spreadsheet file, and you have the columns inside, e.g. x[2] (array x, 'column' 2). This is a one dimensional array. A two dimensional array would be where you have rows; e.g. x[2,3] (array x, column 2, row three). One can have, in theory, as many dimentions in an array as one likes.
Variables
In mathematics the idea of variables are introduced. Variables in a program are very similiar EXCEPT that they may equal different values at different times of the program (this is why indeed they are called variables, they vary). They are used to store values that may be needed for the program, you can declare variables of any of the data type declared above. Think of them as a box with a name, you can change the contents of the box and look inside to see the value at any time:
int x = 5; print x; x = 104; print x; x = 32; print x;
output:
5 104 32
Depending on the programming language you may or may not have to declare variables (in Basic you don't in C you have to). Declaring variables is simply telling the compiler/interpreter that you want to use a variable with that name.
Global and Local Variable
Dependant on where a variable is declared,the variable can be seen by other elements of the program code. There are two types of variable declarations, that is the Global and the Local variables.
Global variables are declared in the root area of the program code, that may be right at the beginning of the code (in C for example). The values stored in these variables will be accessible from any area of the code. This can be useful if you need to access a varibale from anywhere in the program, but if you declare global variables when you don't need to access them all the time, they will sit and take up main memory, thus wasting precious computing resources. Use with care.
Local variables are declared in a sub area of the program code, this may be in a function or procedure. The values stored in these variables will only be accessible from the sub program they are declared in. This can be friendly on computing resources as they are declared when the sub program is called, used, and when the sub program is exited, destroyed. So you only use main memory when you need to store the variable and it does not waste main memory like global variables do. However if you think you will need to variable outside the sub program you should think of using a global variable.
An easy way to think about local and global variables is to think of them as local and global tv channels. Global channels such as Fox and MTV can be accessed from anywhere in the world, but local tv channels such as Channel 5 or Yorkshire TV, can only be accessed in certain areas.
Special cases could be where you declare a global variable called holder, if you then call a sub routine and in this routine there is a local variable declaration of another holder, you do not overwrite the global variable. What happens is for the duration of the sub routine the local variable holder is in charge, when the sub routine exits, the local variable is destroyed and the original value of the global variable now becomes dominant. Take this code for example
code:
main program code
int holder = 4
print holder
...
subroutine caller
int holder = 9
print holder
end subroutine
...
run caller
print holder
end main
output:
4 9 4
[[Rule of thumb:]] If you want to quickly tell the difference between a global and a local variable use these quick rules.
- If a variable is declared inside a function or a procedure it is a local variable
- If a variable is declared inside a iterative or selective statement it is local
- If the declaration is indented from the left hand boundary it probably meets one of the above criteria and is local
- If it meets none of the above statements and is declared in the main body of code it is a global variable
Constants
Constants are like variables in their declarations and the ability to look at the value stored inside them, however you can not change the values, the value of a constant remains, constant.
constant int x = 34; print x
output:
34
Order of Operation
Program Design
There are several very useful programming statements that you can use. You probably use these in your everyday lives with out even thinking about it
Selection
An important part of programming is the use of selection, that is the ability to do something if a certain criteria is met. This may be as simple as increasing your health bar in a computer game if you eat a chicken drumstick or inserting the cooling rods into the nuclear reactor if the temperature exceeds a certain value.
The most common selection statement is the if statement, the idea is that you compare a value to some criteria, if the value and criteria match then you proceed in a certain way, otherwise you do something else. For example:
If Hungry Then Eat Else 'Go Out' End
The other type is the Case statement, this can be summarised by several if statements where the value is compared to several criteria and the action of first criteria matched is performed, otherwise a default action may be performed.
Case Enter Restaurant and pick up menu If Egg and Chips available Then Order Egg and Chips End If If Pie and Chips available Then Order Pie and Chips End If If Curry and Chips available Then Order Curry and Chips End If If Pizza and Chips available Then Order Pizza and Chips End If Default Leave hungry End
Iteration
An incredibly important part of computing is the idea of iteration, that is repeating the same thing again and again. You probably use iteration every day. Take writing lines in a detention for example; you write some lines, check to see if you have met the line limit, and if you haven't you write some more lines, check if you have met the line limit and so on, until you do meet the line limit and then you can stop. There are three main sorts of iteration.
The while loop: For example:
While Hungry Do Eat End
Another type of while loop is a Do-While loop. This is slightly different from the While loop in that you perform the task before you check that you have to perform the task:
Do Eat While Hungry End
The most complicated tool you may meet is the for loop. This is a glorified While loop and don't be put off by how complicated it looks.
For (start with Empty stomach, Is stomach empty?, Eat) Wipe mouth
Procedural Code
Procedures and Functions are very slightly different. Functions return a value whilst Procedures do not. An easy way to remember this is by saying that functions are fun, if you call them they will send you something back, procedures return nothing.
Functions - note the return value
code: a = addtogether(2,3) + 4 print (a)
output: 9
Procedure - note the lack of value returned by the procedure
code:
addtogether(2,3)
proc addtogether(a,b)
{
print(a+b)
}
output: 5
To communicate between different parts of the program and to pass variables to the the functions and procedures we use Parameters. For example
Function addtogether (number1, number2)
{
return: number1+number2
}
where this code will add together the numbers 1 & 2.
Object Oriented Code
Structural Concepts
Methods
Objects
Call Stack
FIXME Expand this article. NB I cannot guarantee the accuracy of the information here, nor how relevant it is to the A Level Syllabus. It is worth knowing, anyhow. if it makes no sense to you then there are plenty of tutorials out there!
Object Orientated code is code which forms resides in blocks. An object, such as a class is declared, similar to how one would declare a variable.
class myClass {
public:
void SayHello(string text) {
cout << text;
return void;
}
} anInstanceofmyClass myClass;
The above code declares an object (of type class) called myClass.
Within myClass a function is declared called SayHello(text), with protection level public (as opposed to protected, or private. Protection layers are effectively the same thing as local and global terms as used for variables. 'Public' means that the function is global, and can be accessed wherever an instance (creation) of the class exists. An object (by which I mean a variable, class, structure or any defined thing in memory) declared with modifier 'private' can only be used, called or accessed by something in that class, e.g. if I declared a private variable in myClass called text it could only be accessed by another Object within myClass, such as the SayHello() function. Protected is the protection modifier inbetween public and private. It can only be accessed by something within the same class, or by an object within a class derived from its class. Derivation, or Inheritance, as it is more often called, is a powerful feature or Object Orientated Programming (OOP), which basically means passing on the objects in one class to a 'child' class. The child class can have its own objects, as well as the objects it recieved from as many 'parent' classes as required. It can also redefine these objects within itself, e.g. SayHello() no longer takes a variable, it prints the text "hello" on the screen without input. I hope this is all making sense to you!
After the class is defined, as instance (Object) of the class is created, called anInstanceofmyClass. One can create as many instances of a class as one likes, e.g. anInstanceofmyClass1, anInstanceofmyClass2, anInstanceofmyClass3 myClass; To call the SayHello() function, one would type anInstanceofmyClass.SayHello("Hello Text"); anInstanceofmyClass1.SayHello("") and anInstanceofmyClass2.SayHello("") both do the same thing.
Introduction to Information and Data Representation
What is Data and Information?
You may have used the words data and information to mean the same thing in everyday conversation, but it is very important that you know the difference between the two when it comes to computers. Roughly speaking data is the raw stream of 1s and 0s inside the computer and information is when the computer makes sense of this stream. It is interpretation of data in computers and different ways of storing information, that we shall now cover.
Consider data as an encoded form of information and information as any form of communication that provides understandable and useful knowledge to the recipient. - AQA[2]
Data
"Data consists of the raw facts and figures that a computer will process into useful information"
Sources of Data
Data can come from a wide variety of areas, but a good way to think about it is data comes from anywhere where there is an input into a computer. This may be from a keyboard, a scanner, a microphone or a disk drive, amongst many others.
Direct and Indirect Data
Data may be collected with a desired purpose in mind, for example collecting data from a weather station. This kind of data collection is called direct data collection. Other times data may become useful for reasons that it was not originally collected for. This is called indirect data collection. An example of this could be, "The data collected above is used to record where a particular video is" this would be an example of direct data and and example of indirect data would be "The data collected is used to build up a profile of the members for targeted advertising".
Information
Information is meaningful data
| Denary | Binary | BCD | ASCII |
|---|---|---|---|
| 0 | 00000000 | 0000 | 0100 0000 |
| 1 | 00000001 | 0001 | 0100 0001 |
| 2 | 00000010 | 0010 | 0100 0010 |
| 3 | 00000011 | 0011 | 0100 0011 |
| 4 | 00000100 | 0100 | 0100 0100 |
| 5 | 00000101 | 0101 | 0100 0101 |
| 6 | 00000110 | 0110 | 0100 0110 |
| 7 | 00000111 | 0111 | 0100 0111 |
| 8 | 00001000 | 1000 | 0100 1000 |
| 9 | 00001001 | 1001 | 0100 1001 |
| 10 | 00001010 | 0001 0000 | 0100 0001 0100 0000 |
| 11 | 00001011 | 0001 0001 | 0100 0001 0100 0001 |
| 12 | 00001100 | 0001 0010 | 0100 0001 0100 0010 |
Consider data as an encoded form of information and information as any form of communication that provides understandable and useful knowledge to the recipient.
Number Representation Systems
Binary number system
Describe the representation of unsigned decimal integers in binary. Perform conversion from decimal to binary and vice-versa. Pure binary representation of decimal integers
Binary-coded decimal (BCD) representation
Describe the representation of unsigned decimal integers in binary-coded decimal. Perform conversions from decimal to BCD and vice versa. Explain advantages of BCD.
Information Coding Schemes
ASCII EBCDIC Unicode
Describe standard coding systems for coding information expressed in character form and other text-based forms. Differentiate between the character code representation of a decimal integer and its pure binary representation.
Introduction to Communication and Networking
Definition of this section is available at [3], page 19.
Communication Methods
Serial
Like a single lane road, all the cars arrive one after another. There is only ever one car going through the check point at any one time.
Parallel
Define both serial and parallel methods and illustrate where they are appropriate. Consider the effect of distance on the transmission of data.
Baud rate
The speed at which telecommunicated data is transmitted, measured in bytes-per-second (BPS).
Bit rate
The rate at which bits are transmitted over a communication path. Normally expressed in bits per second (bps). The bit rate should not be confused with the data signaling rate (baud), which measures the rate of a signal changes being transmitted.
bandwidth
A measure of information or carrying capacity of a signal, expressed as the width of the spectrum of that signal in Hertz..
Asynchronous data transmission
The ASYNCHRONOUS (ASYNC) format for data transmission is a procedure or protocol in which each information CHARACTER or BYTE is may be transmitted and received at irregular and independent time intervals. The characters or bytes may also be transmitted as a contiguous stream or series of characters.
Start and stop bits
Describe the purpose of start and stop bits in asynchronous data transmission.
Parity Bits
Parity is a system in which we use a parity bit to check for errors in a communicating system. Parity bits are generally the most simple way of checking for errors. At the end of a byte sent, an extra bit will be added to the end of the byte. We use two different types of parity bits. These are called even and odd parity bits. If we are using even parity, the bit on the end will ensure that the number of ones sent in the previous data is even. If we are using odd parity, then the bit on the end will ensure that the amount of ones in the sent data is odd.
Handshaking
Handshaking is an automated process of negotiation that dynamically sets parameters of a communications channel established between two entities before normal communication over the channel begins. It follows the physical establishment of the channel and precedes normal information transfer.
Protocol
A protocol is a set of rules which computers use to allow them to communicate. There are many different communications protocols, including WiFi (a low level protocol that stipulates how bits should be converted into radio signals), and IP (a higher level protocol which provides addresses for different locations on a WAN, such as the internet).
Modem
A modem is a piece of electronic equipment that takes data from computers and superimposes it onto the carrier signals of public telecommunications systems. This process is called modulation. The equipment also takes previously modulated data from the public telecommunications system and returns them to state that can be read by computers. This process is called demodulation. Modems can be either built-in units or plugged-in units
Networking
Local area network (LAN)
Bus
Ring
Star
Wide area network (WAN)
The Internet
Intranet
Network adapter
Leased line
==Dial up== networking Candidates should be familiar with LAN topologies but will not be required to know details of their operation. Candidates should be aware of the advantages and disadvantages of each LAN topology. Candidates should be able to compare local area networking with standalone operation.
Uniform Resource Locator (URL)
Describe the term URL in the context of Internetworking. .
Domain names
IP addresses
Explain the term domain name and IP address. Describe how domain names are organised
Principles of Hardware, Software and Applications
A-level Computing/Principles of Hardware, Software and Applications
Practical Systems Development (Short practical project)
CPT3 as is the course reference is a practical based project, normally based upon a database of some description but a pure-coding or part-coding, part-database project are also acceptable. This is examined in the summer of the first year of study.