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.