Computer Science- Unit 2

How can the binary data be transmitted?
When the computer turns it into a steam of on/off signals so they can be transmitted ( send from one place to another ).
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What are 3 examples of a transmission medium?
Electrical pulses that travel down a metal cable, light pulses that travel down a fibre- optic or wireless signals that are sent as EM waves and can travel through any medium.
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What is data transmission used for?
Data transmission is used to link computers, so they can send and share data. For example: the internet is based along long communication links, different parts of a computer share data by short communication links.
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What is Simplex, duplex and half- duplex?
Simplex (one way link communication- it can only go one way- e.g. radio - printer), Duplex (two way communication link- it can go both ways at the same time- e.g. a phone call), Half- duplex ( 1 signal at a time e.g. walkie- talkie)
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What do cables do and what are the 3 types?
Cables connect devices together and send signals. Twisted pair: pairs of copper wires individually insulated and the twisted together. It is inexpensive, not suitable for links, doesn't reduce electrical interference, inexpensive and convenient.
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What are the three types of cables? (continued)
Coaxial cable : metal cable, layer of insulation, layer of metal. Protected against interference but more expensive and less flexible (used close to radio). Fibre- optic: expensive, not affected by electrical interference- long- distance links.
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What is serial transmission?
When the bits are sent one at a time and all travel through the same transmission medium (single wire or wireless) one after the other. - most reliable (bits are kept separate from each other- long distance). But it can take longer to transmit.
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What is parallel transmission?
When several wires are used at the same time, each wire carries a bit- all bits in a byte can be sent/ arrive at the same time. Quicker (several bits / time),not accurate microscopic differences in wires= transmit at different speeds. Short distances
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What is an Integrated Circuit (IC)?
A collection of microscopic electronic circuits sealed into a plastic or ceramic package. Different ICs are used for different tasks, but mostly for data storage. Different ICs are connected by data buses ( wired connection ), really quick.
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What are the advantages and disadvantages of using parallel transmission as a data bus?
The buses inside the CPU and between the CPU and the RAM use parallel. Adv: the speed (the speed od this will affect the speed of the computer). Dis: multiple wires are used so it takes up more space.
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What are peripherals and how are they connected?
Additional devices that a computer needs, which have to be connected to the processor by data buses ( permanent wiring, plug- in cable or wireless connection). Peripherals use serial, as a high speed isn't needed and its also cheaper - single signal.
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Why use USB for all peripherals?
Its a standard connection, and used by most modern computers so more people will buy the peripheral- more practical.
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How can transmission errors be caused?
By flaws in the medium (imperfections in wire) or by external factors (electrical fields). But we can design systems to reduce these errors as all types of transmission media can be affected by these errors.
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Why are transmission errors so dangerous?
Because they can have serious effects, changing one bit of data will alter the value of the binary number , all the signal will be wrong.
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Examples of errors in transmission:
Some of the bits are lost, some are gained. Transpostion-a 1 changes to a 0 and a 0 to a 1. Transcprition- copied out wrongly.
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How are the transmitter and receiver used in data transmission?
Transmitter: has the data to start with and sends it. The receiver: the device that gets the data after transmission (check the accuracy of the data- if an error is found it will ask the transmitter to re-send the data).
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What is Automatic Repeat reQuest and how does it work?
The process where error checks methods are used- to ensure correct transmission of data. Transmitter sends data, receiver checks it, if no errors it will send an acknowledgment, if transmitter doesn't receive an acknowledgment= send again.
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What is parity ?
Means whether a number is odd or even. Used to check if data has errors in it. Transmitter counts 1 and adds an extra bit to ensure that there are an even number (even parity). The receiver counts the 1s, if odd number = transmission error.
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What is odd parity?
The same as even parity but there are an odd number of 1s. The transmitter and receiver have to use the same method.
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What are the disadvantages of parity check?
If there are two errors in a byte then it will fail and won't detect transposition errors.
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What is Check digit?
Similar to parity but added at the end of a deanery number, it is worked out from the digits in the number. The simple method of calculating it : add up all digits, divide the sum by 10, remainder is used as the check digit. (mod 10). mod 11, 10= X.
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What is check sum?
Way of checking a group of numbers the check digit is the sum of the digits. You can use it even f the sum doesn't represent a real sum. (hash total)
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What is the internet and what do you need to have to be connected it it?
Connected computers can share data through data transmission links the Internet is a system of computer connections that covers the whole world. A data transmission connection, Internet software and shared protocols.
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What is an Internet Service Provider (ISP) ?
Most people are connected to the Internet through an ISP. They are mostly commercial companies that offer a connection in exchange for a fee. Services: send signals between Internet and computer, provide email service and hosting a web page.
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What does Software mean?
The instructions that let your computer carry out actions. Several softwares are used to connect you to the internet. It turns signals that come and leave into an understandable way. The most common internet software is a web browser.
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What are protocols?
Protocols are communication standards. Standard rules about how data is tuned into signals. All computers that connect to the internet use the same protocol (TCP and IP)
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What is the world wide web?
A collection of all web pages in the world. Most popular service through an internet connection.
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What is a web page?
Multimedia (many different types of data- text, images, sound, video) document that you can read over the internet . They are created in HTML an can be viewed by a web browser.
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What is a website?
A collection of webpages stored on a web server anybody with an internet connection can connect to te website and look at the web pages.
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What is a web server?
A computer that is permanently connected to the internet. It hosts web pages (holds the content of the web page in its storage). It will send the content of the web page to another computer along the internet.
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Web Addresses
Every web server has its own IP address, and a number of names. Every website and web page hosted by the server has its own URL ( contains the web servers name ).
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What is a web browser?
(Chrome...) A software that lets you look at web pages. You type the URL code and the web browser will get its name from the code, connect to the server, transfer a copy onto your computer, display so you can interact. HTML - content.
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What are the most common shared protocols?
HTTP- allows web pages to be shared. IP- gives every web server an address.
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What is HTML (hypertext markup language)?
A mark up language ( add descriptions (tags) to text). The tags tell a browser how to display the content of the web page.
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Why do tags come in pairs?
Because one tags turns a feature on and one turns a feature off.
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What are the different types of tags?
Structure: control the layout of the web page (tile, headings, paragraphs...). Presentation: change how the web page is displayed (or you can add the command- style)
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What is a hypertext?
A text that makes a link to a new web page. When you click on them you web browser will connect to the linked page and it will be displayed in your browser. In this way you cab browse moving from one website to another.
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How do you make a website?
A web hosting service will help you. The page of your site will be stored in their storage (publishing) . It will provide software that will make it easy to design the web page - instead of typing tags you chose features, turned into HTML by software
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What are hyperlinks?
A key feature of all web pages. It is a piece of text that when you click on it your browser re directs you to a new web page or a different part of the same web page and displays it on your screen.
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What is HTTP (hypertext transfer protocol)?
Is the protocol that makes hyperlinks work, used by all web servers and all web browsers - making links work in all web pages. With it the www wouldn't work.
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What us HTTPS?
It stands for HTTP secure (extended protocol) and has extra features of authentication (checking if a website is fake) and encryption ( private and important details are put into a secret code so that nobody can see what you are sending).
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What are cookies?
Sometimes websites need data that relates specifically to you but HTTP doesn't transmit details. So websites use cookies. When you use a website it collects key data, this is saved as a small binary file in your computer. Next time goes to the site.
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What are the main Internet protocols?
Transmission control protocol- controls the way data packets are transmitted. Internet protocol- make sure that data packets go to the right place.
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What is an IP address?
A number given to every device connected to the internet. Finds a route to the local area network. IP addresses are stored by a service calles Domain Name System.
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What is URL (uniform resource locator)?
Every web browser has an address bar, where you enter the URL code the browser will once to the web server.
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What is the URL made of?
The protocol used (http or https), domain name (identifies server and the web site), the path name (web page) and top- level domain (.com)
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What is a domain name?
Identifies the server that hosts the website and the website itself.The top-level domain code tells you information about the type of business or the country where is comes from. Internet Assigned Number Authority- maintains top- level domains.
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What is a MAC address?
Media Access Control- identifies a single device such as a computer or a printer. Often shown in hexadecimal form.
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Staying Safe Online
Do not use 1234 or password, make sure you remember, do not use the same password and keep it private. Think before writing something online as it stays there forever. If a bully tries to contact you block him. Watch out for tricks, don't open files.
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What is malware?
Malicious software E.g.(virus- set of computer commands, attaches to a file that is already there and copies into other files.)
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What can a virus do and why make them?
Delete files, wipe entire storage, alter settings and make your computer carry out actions. Sometimes they are a joke and others they are used to steal money or to harm enemies.
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What is spyware?
Special type of malware that records everything you do on your computer.
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How does different malware stay hidden?
Worm: malware in its own file. Trojan: malware disguised as a good file, Rootkit: changes operating system so you can't spot it, Backdoor: switches off security letting malware in.
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What is hacking?
When data links are used without permission to look at or change the data on your computer.
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Why use anti-virus software and what does it do?
Malware always hides so you can't delete it . It will check files, scan the computer, delete malware and warn you about risks. It has to be updated regularly to keep up with changes, new malware might've been invented.
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What is Spam?
Bulk undated email, sent using automated systems.
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What us an Internet filtering?
Blocks unsuitable content.
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What is a firewall?
Software designed to screen all data that comes from the internet. Traps every packet of data and checks it, only passes data that follows the rules. Almost every internet connection uses some type of firewall
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Other cards in this set

Card 2


What are 3 examples of a transmission medium?


Electrical pulses that travel down a metal cable, light pulses that travel down a fibre- optic or wireless signals that are sent as EM waves and can travel through any medium.

Card 3


What is data transmission used for?


Preview of the front of card 3

Card 4


What is Simplex, duplex and half- duplex?


Preview of the front of card 4

Card 5


What do cables do and what are the 3 types?


Preview of the front of card 5
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