Keywords

Databases

Any collection of data, or information, that is specially organized for rapid search and retrieval by a computer. Databases are structured to facilitate the storage, retrieval, modification, and deletion of data in conjunction with various data-processing operations. A database management system (DBMS) extracts information from the database in response to queries.

Serial file

A file where the records are held and accessed in sequence but where they are not sorted on any key field and the order is random.

Sequential file

A sequential file is one which must be read in serial order; processors cannot skip around or begin to read or write to a sequential file in any other direction but forward.

External view:

 This is the highest level view, as seen by the user. This level of view describes only one part of entire database that you specifically want to see.

Conceptual view:

 This level describes what data is actually stored in the database. This level contains information about entire database in text form.

Physical level:

This is the lowest level of view at which one describes how the data is physically stored. For example this could be in hex or binary.

 

Flat file

A flat file database is a database that stores data in a plain text file. Each line of the text file holds one record, with fields separated by commas or tabs. It uses a simple structure, usually a table.

 

Hierarchical file

A hierarchical file system is how drives, folders, and files are displayed on an operating system. In a hierarchical file system, the drives, folders, and files are displayed in groups, which allows the user to see only the files they're interested in seeing. For example, in the picture the Windows directory (Windows\) folder hierarchy

that contains the System32, Tasks, and Web folders. Each of these folders could have hundreds of their own files, but unless they are opened the files are not displayed.

 

CPU

CPU

The central processing unit is the core of the computer, it does all the processing.
It has two main components: the control unit, this uses to direct and execute instructions in stored programs,  the ALU(arithmetic and logic unit) this carries out all arithmetic and logical operations including addition, subtraction and comparisons.

 The CPU also runs an endless fetch execute cycle. This is when the CPU fetches the next instruction before decoding it and finally executing it. this happens infinitely until you turn the computer off.

Clock speed

The clock speed is the speed that the microprocessor executes each instruction or each vibration of the clock. The CPU requires a fixed number of clock ticks, or cycles, to execute each instruction. The faster the clocks rate, the faster the CPU, or the faster it can execute instructions. Clock Speeds are usually determined in MHz, 1 MHz representing 1 million cycles per second, or in GHz, 1 GHz representing 1 thousand million cycles per second. The higher the CPU speed, the better a computer will perform, in a general sense.

Cache size

This is very fast memory that can work at a similar speed as the CPU, however it is very expensive and can only be used to store data waiting to be processed by the CPU.

Internet

The internet

The internet is a network that links computer networks all computers over the world using The Internet is used to send information quickly between computers around the world. It has millions of smaller domestic, academic, business, and government networks and websites, which together carry many different kinds of information and services. So in other words, the Internet is a network of networks.
No one owns Internet, although several organizations the world over collaborate in its functioning and development. The high-speed, fiber-optic cables (called backbones) through which the bulk of the Internet data travels are owned by telephone companies in their respective countries. 

World wide web

The World Wide Web is a network of computers that serve webpages. The World Wide Web is a major component of the Internet, along with email, usenet, ftp, and some other minor protocols. The term "world wide" refers to the global nature of the World Wide Web, and the term "web" refers to the interlinking of documents by means of hypertext. In simple terms, this means that documents on the Web (or WWW for short) can reference, or link to, other documents by simply stating on which machine they reside, and where on that machine.

TCP/IP

Standard Internet communications protocols that allow digital computers to communicate over long distances. The Internet is a packet-switched network, in which information is broken down into small packets, sent individually over many different routes at the same time, and then reassembled at the receiving end. TCP is the component that collects and reassembles the packets of data, while IP is responsible for making sure the packets are sent to the right destination. TCP/IP was developed in the 1970s and adopted as the protocol standard for ARPANET (the predecessor to the Internet) in 1983.

Redundancy

The idea that the internet will never go as it is hosted everywhere and is all around us and hosted by anyone shared.

 

 

Digital and Analogue internet 

A dial-up modem converts digital signals from a computer to analogue signals that are then sent down the telephone line. A modem on the other end converts the analogue signal back to a digital signal the computer can understand.

The maximum theoretical connection speed is 56Kbps. Dial-up is very slow by today’s standards and in real world use will typically result in a download speed of roughly 5KBps.
Phone calls cannot be made whilst connected to the Internet.

ISDN

An ISDN (Integrated Services Digital Network) capable phone line can provide connection speeds of up to 128Kbps (dual channel) using a terminal adapter often referred to as an ISDN modem. The terminal adaptor removes the need to convert digital signals to analogue signals before they’re sent down the telephone line, this results in a more reliable Internet connection.

ADSL

ADSL (Asymmetric Digital Subscriber Line) provides connection speeds of up to 24Mbps and uses a telephone line to receive and transmit data.

 

Cable

Cable companies do not use traditional telephone lines to provide broadband Internet access. They have their own network, a combination of co-axial copper cable and fibre optic cable.
With their purposefully built infrastructure cable companies are able to provide speeds of up to 50Mbps - considerably faster than the highest available ADSL speed (24Mbps).
The making and receiving of phone calls is not affected because the telephone line is not used.

Networks

LAN

A LAN is useful for sharing resources like files, printers, games or other applications. A LAN in turn often connects to other LANs, and to the Internet. Local area networks are supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home.

 

Advantages

• They are faster than wireless networks
• many computers in the same LAN have access to the same files, folders and peripherals like printers
• they are cheaper

Disadvantages

•  Special security measures are needed to stop users from using programs and data that they should not have access to;  
• Networks are difficult to set up and need to be maintained by skilled technicians.  
• If the file server develops a serious fault, all the users are affected, rather than just one user in the case of a stand-alone machine.

Hardware

 

NIC

An adapter circuit board installed in a computer to provide a physical connection to a network.

 

Hub

In computer networking, a hub is a small, simple, inexpensive device that joins multiple computers together. Many network hubs available today support the Ethernet standard. Other types including USB hubs also exist, but Ethernet is the type traditionally used in home networking.

 

Router

A network device that forwards packets from one network to another. Based on internal routing tables, routers read each incoming packet and decide how to forward it. The destination address in the packets determines which line (interface) outgoing packets are directed to.

 

Switch

A network switch (sometimes known as a switching hub) is a computer networking device that is used to connect devices together on a computer network by performing a form of packet switching. A switch is considered more advanced than a hub because a switch will only send a message to the device that needs or requests it, rather than broadcasting the same message out of each of its ports.

Wireless access point

In computer networking, a wireless Access Point (AP) is a device that allows wireless devices to connect to a wired network using Wi-Fi, or related standards. The AP usually connects to a router (via a wired network) as a standalone device, but it can also be an integral component of the router itself.

Protocols

When data is exchanged through a computer network, the rules system which the computer follows is called a network protocol.

Topology

There are three main 

Bus topology:

the advantages of a bus topology are that there is one common linking cable,nodes connected off the cable and it is cheap

slows down with heavy traffic

lots of data collisions

breakage to cable affects whole network

limited distance possible

Star topology:

shared link to servers

most common

few data collisions

fast

can set up independent segments

Ring topology:

one common liknking cable

passes all nodes

one direction traffic

fast performance

Homework- 10/03/15

When a user types a certain website's domain name such as http://www.neatorama.com into their browser the DNS server translates this address into an IP address such as "23.239.6.122" in this instance. This IP adress is used to locate the server of that websit and give you access to it.

Within the DNS server there is a table of domain names that are linked to IP addresses. There are a lot of DNS servers for the internet so if your local DNS server does not have the domain name you want to access listed, the request can be forwarded to more servers.

The advantage of DNS servers is that you do not need to remember a long number to go to each website but only an address. However, disadvantages are that it is a centralized server that you have to connect to every time you access a new website. This also means that the breakdown of key DNS servers could seriously harm the world wide web. Finally, a common form of computer hacking is done by DNS spoofing, meaning you are sent to the wrong IP address and therefore website that could be malicious or harmful.

SOFTWARE

System software

 

Types of software

 

System software:

operating system, device drivers, firmware, servers, utilities, interfaces

Developer software:

Programing languages

utilities

 

Applications

Web browsers, Games

 

 

Multitasking

 

Allows the computer to make best use of the CPU. A multitasking operating system allows more than processes in the RAM at a time, they can be in multiple states:

Running-

CPU is currently processing this program

 

Runnable-

Ready to go in the queue, its waiting for current program to finish

 

Waiting-

Waiting to go in the queue to become runnable 

 

 

Operating system

An operating system is a collection of software that manages the hardware in a computer.

 

Windows: the most popular OS that is used in most desktop and laptop computers. it also has a GUI that allows all programs running under windows to look the same.

 

UNIX: A OS used on servers and workstations, traditionally it ha a command line interface.

 

MacOS: Apple Computers’ own proprietary operating system based on UNIX

 

LINUX: designed to behave like UNIX but was developed separately and is the basis for many other operating systems.

 

Operating systems also have supporting software to manage various aspects of the system:

Utility software

–is often loaded with the operating system

–comes as small-scale programs used to carry out simple maintenance tasks.

Security

–Anti-virus software to detect and remove viruses that could damage the data on the computer;

–Anti-spyware to detect and remove spyware such as a Trojan that logs key strokes to steal passwords and other sensitive data;

–Firewalls that restrict incoming and outgoing access to certain network addresses.

Maintenance:

Disk organisation tools allow formatting and management of files on disks, for example:

–Disk defragmenters: As files are deleted and added, the data gets spread around the disk, leaving gaps. The defragmenter moves the files to put all the free space together to improve access speeds.

–Other utilities include:

–Archive

–Backup

–Data compression

–Disk cleaners

–Network utilities

Development software

Editors:

These are used to write programs, these are usually just word processors that don't save formatting. Editors will often have features to help organise the code by detecting program constructs and indenting loops, using different colours for key words and automatic line numbering.

Compilers:

These translate the high-level code used by the programmer into the machine instructions required by the computer. The high level code produced by the programmer is called source code, and the machine instructions created by the compiler, object code.

Interpreters:

These also translate the high level code into machine instructions but they translate the code one line at a time and execute it, instead of translating the whole program to create the object code.

Assemblers:

These are used to translate assembly language programs into machine instructions. Assembly language is not machine code but each assembly language instruction translates to just one machine instruction.

Linkers:

These are used to connect sub programs that are often written using different languages or tools the linker combines all these bits of code to make them work together.

Applications software

 

Applications are programs that do real world jobs:


There is a huge range of applications (or apps) to do all sorts of jobs and for a wide range of devices.

Office software

–Word processor

–Spreadsheet

–Presentation software

–Drawing package

–Database management software

Enterprise software

 This may include standard office applications alongside specialist items, for example:

–Stock control

–Payroll

–Electronic Point of Sale

–Customer management

Questions

1. An IDLE can help a programmer by checking for syntax errors in his code and by making it easier for new users to work out what the code does.
2. a) open source software is software that anyone can use or edit to make better and can be accessed for free
b) two advantages are that it is free and that anyone can add to it to improve it however two disadvantages are that there is no guarantee of updates because it is being developed for free and that most open source software isn't reliable.
3.
a) an editor is a piece of software used to edit the code of a program and is used by developers.
b) a disc defragmenter is a piece of software used to free up space on a hard drive by organising your files so that you are using up a your hard drive efficiently.
c) a firewall is a real-time protection against viruses infecting your PC.

A Computer System

System

A system is an assortment of software and hardware that, from physical or digital input, creates an output that is intended and useful to you. For a system to work you first need an input, then for the system to process the information, then for you to get the output. If a system has no output it is useless.

Reliability

Reliability is the measurement for how much faith and trust you have in a system working. If a system you use will work without fail it is reliable however if your system has a chance of breaking then it isn't reliable, however reliability cannot be guaranteed. This can be extremely dangerous as some systems (like in aeroplanes) could result in death if they aren't reliable.

 In most systems reliability is important (you don't want your pc to crash whole doing something) however in some systems that we rely on every day reliability is one of the most vital components. For example on a rocket if the computer failed everyone

Input> Process> Output

Embedded Systems

 An embedded system is a computerized system, usually within a larger device that has a specific set of functions or tasks. This could be anything from temperature control in a washing machine to air bags, abs or traction control in a car. Embedded systems are useful because they have low power, low cost and can still have a sophisticated functionality.

Regulations and Data Protection

Regulations exist to protect your identity from being stolen, for example in 2010 in fewer than 6 months $900,000 of one mans debit card was taken out of his account after they put keystroke malware on his computer. "It was nasty," he said, admitting that he even contemplated suicide. "I just couldn't take it. I didn't feel like a man anymore. I was violated and I didn't know what to do."

The data protection act contain eight principles that say data must be:

1. Processed fairly and lawfully.

2. Obtained for specified and lawful purposes.

3. Adequate, relevant and not excessive.

4. Accurate and up to date.

5. Not kept any longer than necessary.

6. Processed in accordance with the “data subject’s” (the individual’s) rights.

7. Securely kept.

8. Not transferred to any other country without adequate protection.

The Copyright, Designs and Patents Act says that you cannot take things (like music, films and software) without their permission. 95% of music downloaded online is illegal; 42% of software in the world is illegal; the three most downloaded programs illegally are Adobe Photoshop, Microsoft office and Nero 9; 91% of files on Cyberlockers like Megaupload, Rapidshare and Mediafire are copyrighted material; 2/3rds of bit torrents online are copyrighted material.

  http://www.marketwatch.com/story/the-rise-of-identity-theft-one-mans-nightmare-2010-02-10
http://dataprotectionact.org/1.html
http://www.infographicsarchive.com/interesting-facts/online-piracy-in-numbers-facts-and-statistics/

http://www.infographicsarchive.com/interesting-facts/online-piracy-in-numbers-facts-and-statistics/

 

Kernel

 

A kernel is the lowest level in an operating system. It controls the hardware. It manages the inputs and outputs of the operating system. It is also responsible for the management of the hardware like the memory.

 

Binary Logic

 

 In an AND gate only when Both inputs are 1 do you get an output of 1.

In a Not gate the output is the opposite of the input.



In an OR gate you will always get an output of 1 unless both inputs are 0.

In the AND NOT gate the output is always the opposite of the and gate (where there was once a 0 there is now a 1)

Binary is a number system using only ones and zeros. One being ON and zero being OFF. These systems also use logic gates. These are used to manipulate the signals.

 

Ram

Ram is "random access memory" and the main source of memory in a computer system. RAM is needed to run any application or operating system. This means that the more RAM the more applications can run at any one time resulting in better performance. When a program is loaded it goes from the hard disk to the RAM then finally to the CPU via the cache,

 

There is two types of RAM:

Dynamic RAM- Only has one transistor and capacitor that can hold a small charge for a few milliseconds.

Static RAM- does not need to be refreshed as they have four or five transistors that have a constant charge.

 

Input and Output Devices

An input device is anything that can control the output device. Without input or output devices you couldn't control a computer or see/hear etc. what the computer wants you too.

An example of an input device is the mouse which navigates your pointer on the screen (output device).

Some input or output devices are for users with specific needs, for example the braille keyboard which is a specialist keyboard for people who have a visual impairment and cant see a normal keyboard. 

 

Secondary Storage

Secondary storage is a non-volatile way to store data. your primary storage is your hard drive but then your secondary storage is another way to store your data outside your hard drive. you do this because secondary storage can be useful for many reasons.

1. Portability, You can buy a small 16GB usb stick for £7 which you can carry around with you wherever you go.

2. Speed, You can buy a SSD for £45 which are much faster and reliable than your normal hard drive.

3. Durability, most secondary storage is more durable than normal hard drive.

 

Binary

 

 Binary is a number system using just ones and zeros to represent all denary numbers in base 2. Numbers form 1 to 15 are represented in four numbers or a "nibble" and numbers 15 to 255 are represented as 8 numbers or a "bite". The four or eight numbers represent denary numbers like this:

128/64/32/16/8/4/2/1

 

Therefore an example would be 128=10000000, or 50= 00110010.

 

Hex

Hex is a base 16 number system used to represent binary in a simpler form.  The numbers from 0-9 are represented as themselves but from 10-15 are represented as letters. Hex works by the first number being what you imes by 16 and the second number is what you add on after, for example the hex number 32 means 3*16+2=50.

 

ASCII

ASCII (American Standard Code for Information Interchange) is a set of 127 codes that represent all characters on an English keyboard (56 UPPER and lower case alphabertic characters, all numbers 0-9, 32 punctuation and other symbols (space, !"£$%^&*()_) and 32 codes reserved for non-printable control codes) there is also an additional code for "null" (00000000). ASCII was first used for telegraph systems in the 1960s.

 

 

Instruction Sets

An Instruction Set is a set of programming instructions, which allow a computer system to carry about commands necessary for operation. Instruction Sets vary by the design of a processor. A program instruction has two parts, the instruction part that tells the CPU what to do (operator) and the data part that the CPU what to apply the operation to (operand). When the CPU fetches the data from the memory it cannot tell the difference between instructions and data but does what it expects to based on the program its running.

 

File sizes

Bit- The most basic unit of information, most commonly a 1 or a 0

Nibble- 4 bits

Byte- 8 bits or 2 nibbles, can represent numbers 0 to 255

Kilobyte- 1024 bytes

Megabyte- 1048576 bytes or 1024 kilobytes

Gigabyte- 1024 Megabytes

Terabyte- 1024 Gigabytes

 

Images

Images are represented digitally in binary where each bit represents a pixel that each have a different colour. Images stored like this are called bit mapped images, the more pixels in a given area the higher the resolution of the image, giving it a higher quality. The higher the resolution the higher the file size as well because there are more bytes. 

Colour depth is the number of colours that can be used to represent a single pixel, for example in a  8 bit image there is 256 colours.

Metadata is data about the data; it is useful to provide extra information about a file, in a image this could be: the height, width, colour depth.

 

Development software

 Editors

To write programs you need an editor, they are cut down word processers that do not save formatting . There are some advanced editors that enable "pretty printing" which can detect errors and make them a different colour.

 

Compilers 

Compilers turn high level code back into machine instructions so the CPU can execute them. Each statement in high level code relates to many machine instructions.

 

Interpreters

Interpreters also convert high level code into machine code but do so a line at a time and execute the code as they go. This uses more RAM and is slower to translate and run one line at a time.

 

Assemblers

Assembly language is a low level code that has a direct correspondence of one line of code to one instruction. Assembly language changes from one processor to another.

 

Linker

In one program there can be many different subprograms made by different teams. Linkers combine these programs together to create one big program.