For data transmission these factors are considered:
The direction of the data transmission (one direction only or both at the same time?)
How many bits are sent at the same time.
Simplex data transmission is in one direction only.
Examples, data sent from: a microphone to a computer, a sensor to a computer, computer to speaker, computer to monitor, webcam to computer.
Half-duplex data transmission is in both directions but not at the same time.
Duplex data transmission is in both directions simultaneously.
Examples: telephone call, VOIP (Voice over the Internet Protocol (Skype)), video conferencing, instant messaging.
Method of transmission
Serial data transmission is when data is sent, one bit at a time, over a single wire or channel (bits are sent one after the other in a single stream). Bits can be transmitted as simplex, half-duplex or duplex.
This method of transmission works well over long distances. However, data is transmitted at a slower rate than parallel data transmission.
Using a single wire there is less chance of interference, so little or none data corruption occurs.
Using a single wire reduces costs.
Bits will still be synchronised after transmission.
Example, sending data from a computer to a modem for transmission over a telephone line.
Parallel data transmission is when several bits of data (usually 1 byte) are sent down several wires or channels at the same time; one wire or channel is used to transmit each bit.
This method of transmission works very well over short distances (over longer distances, the bits can become skewed, which means they will no longer be synchronised).
This method is faster than serial data transmission.
Parallel data transmission is used in the internal electronics of the computer system. The pathways between the CPU and the memory all use this method of data transmission. Integrated circuits, buses and other internal components all use parallel data transmission because of the need for high speed data transfer.
Example, sending data to a printer from a computer using a ribbon connector.
Integrated Circuits (IC)
An Integrated Circuit (aka chip, microchip) uses parallel data transmission for sending data internally. For example, the CPU is an integrated circuit which uses parallel data transmission to send data.
An IC is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material that is normally silicon. The integration of large numbers of tiny MOS transistors into a small chip results in circuits that are orders of magnitude smaller, faster, and less expensive than those constructed of discrete electronic components. The IC's mass production capability, reliability, and building-block approach to circuit design has ensured the rapid adoption of standardized ICs in place of designs using discrete transistors. ICs are now used in virtually all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other digital home appliances are now inextricable parts of the structure of modern societies, made possible by the small size and low cost of ICs. (Source: wikipedia)
Universal Serial Bus
What is USB?
Watch this video
Essentially, the USB cable consists of:
a four-wire shielded cable.
twwo of the wires are used for power and the earth.
two of the wires are used in the data transmission.
When a device is plugged into a computer using one of the USB ports:
the computer automatically detects that a device is present (due to a small change in the voltage level on the data signal wires in the cable)
the device is automatically recognised, and the appropriate device driver is loaded up so that computer and device can communicate effectively.
if a new device is detected, the computer will look for the devie driver which matches the device, if this is not availabllee, the user is prompted to download the appropriate software.
Internet principles of operation
Internet Service Provider (ISP)
Each user makes use of an ISP; these are companies that provide the user with access to the internet. A monthly fee is usually charged for this service. The ISP will set up a user account which will contain a username and a password; most ISPs also give the user an email address.
Before ISPs became common in the ‘90s, internet access was usually limited to users who were part of a university or a government agency.
A Media Access Control address refers to a number which uniquely identifies a device on the internet. The MAC address is rarely changed so that a particular device can always be identified no matter where it is.
A MAC address is usually made up of 48 bits which are shown as six groups of hexadecimal digits:
NN - NN - NN - DD - DD - DD
where the first half (NN - NN - NN) is the identity number of the manufacturer of the device and the second half (DD - DD - DD) is the serial number of the device. For example: 00 - 1C - B3 - 4F - 25 - FE is the MAC address of a device produced by the Apple Corporation (code 001CB3) with a serial number of 4F25FE. Other manufacturer identity numbers include:
00 - 14 - 22 which identifies devices made by Dell
00 - 40 - 96 which identifies devices made by Cisco
00 - A0 - C9 which identifies devices made by Intel
Internet Protocol (IP) adress
Each device on the internet is given a unique address known as the internet protocol (IP) address. This is a 32-bit number which is usually written in the form:
A home computer is given an IP address when it connects to the internet. This is assigned by the ISP and is unique for that particular internet session. The only IP addresses that remain fairly unchanged are web servers.
An IP address can be used instead of typing in the full URL. For example:
would take you straight to the device corresponding to this address.
IP addresses and MAC addresses
The IP address gives the location of a device on the internet, whereas the MAC address identifies a device.
Think of the IP address as your house number and the MAC address as your identification (DNI) number. If you move house your house number will obviously change, same as the IP address. But your DNI will remain the same, same as the MAC address.
Cookies aren’t programs but are simply pieces of data. They can’t actually perform any operations. They only allow the detection of web pages viewed by a user on a particular website and store user preferences.
The information gathered by cookies forms an anonymous user profile and doesn’t contain personal information (such as credit card numbers). Because of the information they do collect, however, they are subject to privacy and security concerns.
Uniform Resource Locator (URL)
HyperText Mark-up Language (HTML)
HTML is used when writing and developing web pages. HTML isn’t a programming language but is simply a mark-up language. A mark-up language is used in the processing definition and presentation of text (for example, specifiying the colour of the text).
HTML uses <tags> which are used to bracket a piece of code; for example, <td> starts a standard cell in an HTML table, and </td> ends it.
HTML structure and presentation
Structure is used to create the layout of the document. Consists of the mandatory parts of an HTML document plus the semantic (meaning) and structured markup of its contents.
HTML tags are added to each element of content in order to provide meaning and context. Further HTML tags can be used to divide a page into logical sections (divisions), making different layouts possible when combined with CSS.
Presentation is the style of the document; i.e. how the document will look.
These two features must be kept separate throughout the designing of a web page. At the end of the design process, the author should have an HTML document (which contains the structure and the actual content) and a separate css (cascading style sheet) file. The css file will contain everything to control the actual presentation of the web page.
Hypertext Transfer Protocol (HTTP)
HTTP is a set of rules that must be obeyed when transferring files across the internet.
When some form o security is used, then this changes to https, The letter s after http refers to: http over secure. It is slower to use https than http.
A web browser is software which allows a user to display a web page on their computer screen. Web browsers interpret or translate the HTML code from websites and show the result of the translation. This can often be in the form of video, images or sound. Most web browsers share the following features:
they have a home page
they have the ability to store a user’s favourite websites
they keep a history of the websites visited by the user
they give the ability to go backward and forward to websites opened
Users can either click on a link, or they can type in the uniform resource locator (URL) manually.
The web browser will break up the URL into three parts:
http:// -> this is the protocol used
www.codingclub.co.uk -> this is the domain name
book2_home.php -> this is the file name
The web browser translates the web server domain name into an IP address which is part of the URL. The HTML code is returned and is shown as a correctly formatted page on the computer screen. It is also possible that cookies may be sent from the web browser to the web server when the code is executed.