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104 Cards in this Set
- Front
- Back
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Define a computer system. |
A computer system is one that is able to take a set of inputs, process them, and create a set of outputs. This is done by a combination of hardware and software. Input --> Process --> Output |
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Describe the importance of computer systems in the modern world.
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Safety - Guiding aircraft, controlling trains, supporting signalling systems, monitoring patient body signs Travel - Smart phone apps, GPS systems, train timetables, flight bookings Business - Orders, stock control, payroll Retail - Online ordering of anything, logistics systems that control delivery of goods Entertainment - DVDs, Blu Ray, MP3 players Communication - Email, chat, social networks, business transactions, mobile phones Education - Virtual Learning Environments, exam marking, unlimited sources of information on the web Politics and government - Campaigns, voting (in some countries), payment of taxes Science - Number crunching, simulations, visualisations |
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Explain the need for reliability in computer systems. |
Unreliable computer systems can be lethal, causing aircraft accidents. They can result in the loss or theft of data. The NHS IT system never delivered what was hoped for.
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Explain the need for adherence to suitable professional standards in the development, use, and maintenance of computer systems. |
Adhering to certain standards makes systems more reliable. If a system is developed according to defined standards, it is more likely to be successful and satisfy users. They also help make sure different computer systems can talk to each other. |
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Explain the importance of ethical considerations considerations when creating computer systems. |
There are codes of ethics laid down by various organisations, they include not undertaking work beyond your capability, not bringing your profession into disrepute, avoiding injuring others, and not taking bribes. |
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Explain the importance of environmental considerations considerations when creating computer systems. |
A lot of energy is wasted in the inefficient generation of heat which has to be removed from the equipment. This is of concern to us because supplies of energy are finite and expensive. E-waste (old computer equipment) contain many toxic and carcinogenic components. Electronic waste is sent to landfills where toxic materials can escape into the wider environment. |
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Explain the importance of legal considerations considerations when creating computer systems. |
Those who keep personal data on computer systems should take care of it and protect it from unauthorised people. People should be able to inspect any personal data held about them to satisfy that it is accurate. It is illegal to gain unauthorised access to computer systems or modify the data stored in them. |
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Define the term hardware. |
Hardware is the term that describes the physical components of a computer system, anything that can be seen or touched. |
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Describe the function of the CPU. |
The CPU fetches and executes instructions stored in memory. |
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How does clock speed affect the performance of a CPU? |
The speed of the fetch execute cycle is determined by an electronic clock chip (3 GHz = 3 billion cycles per second). Processors with a higher clock speed can perform more cycles per second and therefore they are faster. |
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How does cache size affect the performance of a CPU? |
To prevent the CPU from waiting for main memory to supply data, the first instruction of a program is requested by the CPU whilst the remaining instructions are copied into the cache memory. Checking if the required data is in the cache reduces the time taken to access the data. The more cache memory there is, the more likely the requested data has already been requested and copied to the cache memory. |
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How does the number of cores affect the performance of a CPU? |
A duel-core processor has two CPUs working together. They can fetch, decode, and execute instructions at the same time so the computer can process more instructions at a faster rate. |
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Describe RAM. |
RAM is the main memory in a computer. When a program is loaded, it is copied from the secondary storage into the main memory (RAM). The CPU can now access the data and instructions for the program as required. This happens because direct access from the secondary storage is slow. RAM is volatile and the data it stores is lost when the power to the computer is switched off. |
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Describe ROM. |
ROM is able to retain information programmed in by the manufacturer without power. This makes it non-volatile. ROM is often used to store the boot sequence. ROM cannot be overwritten by the computer. |
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How does the amount of RAM in a PC affect the performance of the computer? |
The more RAM there is, the more programs and data it can load at the same time meaning better performance. |
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Explain the need for virtual memory. |
When we need to run more complex programs or several programs at once, the computer will slow down if RAM is being fully used. When there is not enough RAM the computer will use a section of the hard disk as a temporary store for some of the data in main memory. Data in RAM not currently being used is stored on a specific area of the hard disk (called virtual memory), while the data needed will be loaded into RAM. Switching between programs will be slower since the computer has to move data between the main memory and hard disk before it can open the second program. |
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Describe cache memory. |
Very fast and relatively expensive memory. Where main memory will be provided in gigabytes, cache will be provided in megabytes. |
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Describe flash memory. |
Flash memory uses a relatively large electric current to force electrons through a barrier and trap them in a layer on the other side of the barrier until they are reset. It is used as removable memory in a wide range of devices. It is the main secondary storage in portable devices and on some larger installations. The constant writing and re-writing can cause deterioration and even failure. It is low cost and portable. Access to flash memory is not as fast as RAM even though it is a form of RAM, but it is faster than a magnetic hard drive. |
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Discuss how changes in memory technologies are leading to innovative computer designs.
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Storage in computer systems can be smaller. Faster read/write times allows increased performance. Less power consumption allows computers to last longer on battery power. Lower costs allow the ability to install more RAM in basic systems. |
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Why do we need input and output devices? |
Without a way of getting data in and information out, computer systems are of little value. |
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Describe suitable input devices for a wide range of computer controlled situations. |
Keyboard - A device that uses labelled keys to enable input into a computer. Mouse - A device that controls the movement of a pointer on screen, based on its own movement, and allows the user to select an object by pressing a button. Touch screen - A common type of input device where a user touches an icon or symbol to select it directly on the screen. Microphone - Used for inputting speech, communication, or voice commands to the system. Camera - Image or video input for taking photographs or video conferencing. They may also be used for iris or facial recognition in security applications. Bar code scanner - Bar codes can be scanned to identify an item. RFID reader - RFID is an electronic version of a bar code using radio frequencies to transfer information to a reader. They are used in shops but can also track luggage.
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Describe input devices for users with specific needs. |
Eye-typer - For users with limited physical mobility. Puff-suck switch - A switch that can be operated by blowing or sucking a small tube, used by those with severely limited physical mobility. Voice input - For those who find it difficult to use a keyboard. Joystick - For those with limited movement. Foot mouse - For those who have limited hand movement. Braille keyboard - A keyboard with raised embossed patterns on each key that match the standard Braille characters, used by blind people. |
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Describe suitable output devices for a wide range of computer controlled situations. |
Monitor - An visual output that displays message, text, images, or video. Printer - Transfers data into a hard, physical copy. Speakers - Outputs sound for warnings or music. Actuators - A computer controlled device that can make a mechanical adjustment to a system. They are fundamental in aeroplanes. |
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Describe output devices for users with specific needs. |
Screen readers - There are a range of devices used to read a computer screen to assist people with a wide range of visual impairment. Actuators - Create physical movement in response to a computer command and are incorporated into a range of devices for those with limited mobility. Voice synthesisers - Spoken output from a computer can be used for those unable to communicate verbally. |
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Explain the need for secondary storage. |
Most computing needs require general purpose computers capable of performing a range of tasks. RAM is volatile so we lose everything in it when we turn off the computer. ROM isn't volatile but can only be pre-programmed so we can't save any changes. We need a form of storage that we can change and that is not volatile. |
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Describe optical storage technology. |
CD-ROMs and DVD-ROMs are written at manufacture and used to distribute programs. CD-RWs and DVD-RWs have the ability to be written to and are used as secondary storage to transfer files between computers. Optical disks use light from lasers to detect reflections from the surface of the data area on the CD/DVD surface. In CD/DVD-ROMs this is a manufactured and raised area on the reflective layer in the disk. In RW media the writer can modify the surface of the media using a laser. The surface has a dye layer that is changed by shining a laser light at it. The colour difference is detected when it is read. |
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Describe magnetic storage technology. |
The magnetic hard disk is a magnetised rigid plate or stacks of plates with heads to read the data as the platters spin around. They are reliable and cost-effective, providing high capacity at a low cost. |
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Describe solid state storage technology. |
Flash memory is electronically erasable programmable read only memory and has better access times than magnetic disks, has no moving parts to go wrong, and uses significantly less power. It is not able to match the size of storage offered by magnetic hard disks. |
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Define the term software. |
The term software describes a set of instructions to perform a task (program). Programs in general are known as software. |
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Explain the need for the user interface in an operating system. |
Provides a user interface so it is easy to interact with the computer. |
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Explain the need for memory management in an operating system. |
Transfers programs into and out of memory, allocates free space between programs, and keeps track of memory usage. |
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Explain the need for peripheral management in an operating system. |
It is how the computer opens, closes, and writes to peripheral devices such as storage attached to a computer. |
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Explain the need for multi-tasking in an operating system. |
It allows multiple applications to be run at the same time. |
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Explain the need for security in an operating system. |
Provides security through user accounts and passwords. |
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Describe the purpose and uses of computer security utilities. |
An antivirus can be used to defend the PC against spyware. Firewalls can be set up by software utilities and restrict outgoing and incoming access to certain network addresses. |
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Describe the purpose and uses of disk organisation utilities. |
They let you format new disks, move files from place to place, and carry out jobs such as renaming files. After a while files on your hard drive get broken up into fragments. This slows down loading when a new file is split across several fragments. Defragmenters reorganise files so individual files and all the free space are put together. |
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Describe the purpose and uses of system maintenance utilities. |
System information and diagnosis, system cleanup tools, and automatic updating are all system maintenance utilities. |
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Define the term bit, nibble, byte, kilobyte, megabyte, gigabyte, and terabyte. |
Bit - A single binary digit that can be either 0 or 1 Nibble - 4 bits Byte - 8 bits Kilobyte - 1024 bytes Megabyte - 1024 kilobytes Gigabyte - 1024 megabytes Terabyte - 1024 gigabytes |
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Why must data need to be converted to a binary format? |
So it can be processed by a computer. |
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How do you convert from denary to binary? |
Divide by 2 repeatedly noting the remainder value each time until the answer is zero. The answer is the remainder column starting at the last value. |
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How do you add binary integers? |
The same way we add denary numbers. 0+0 = 0, 0+1 = 1, 1+1 = 0 and carry the 1, 1+1+1 = 1 and carry the 1. |
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What is overflow? |
An 8-bit overflow occurs if two 8-bit numbers are added, and the total binary number is bigger than 8 digits. When this happens the CPU drops the overflow digit because it cannot store it anywhere so it thinks 255 + 1 = 0. |
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How do you convert denary into hexadecimal? |
First convert to binary. Split the binary into groups of four digits and find out the denary value if each of those sets of four digits where an individual number. Convert the new denary numbers to hexadecimal. Hexadecimal is when after 9, letters are used so we can get symbols from 0 to 15. |
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Why are hexadecimal numbers used to represent binary numbers? |
It is a shorter way of representing data. It is more readable. |
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Explain the use of binary codes to represent characters. |
The characters available to a computer are its character set. Each character is represented by a binary number. |
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Describe the relationship between the number of bits per character in a character set and the number of characters that can be represented. |
The more bits used, the more characters in the character set. ASCII uses 7 bits containing codes for 127 characters. Unicode uses up to 32 bits containing codes for over 4 billion possible character codes. The 16-but version of Unicode (with 65,000 characters) is sufficient for most purposes. |
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Explain the representation of an image. |
A series of pixels represented in binary. |
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Why is metadata needed for an image? |
It stores things like height, width, and colour depth so the computer can make sense of the binary data. |
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Discuss the effect of colour depth and resolution on the size of an image. |
The bigger the resolution and colour depth, the larger the size of the image. |
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How can sound be sampled and stored in digital form? |
Sampling the sound wave at set intervals and recording the values is how we store sound in digital formats. |
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Explain how sampling intervals and other considerations affect the size of a sound file and quality of its playback. |
If the sample rate increases, more data would be needed but the sound will be closer to the original analogue sound. The bit rate used to store the sampled data also has an effect on the quality of the recording. The bit rate is the amount of space available to store the sampled data per second. |
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How are instructions coded as bit patterns? |
A program instruction has two parts - the instruction or operator, and a data part or operand. |
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How does the computer distinguish between instructions and data? |
The program must tell the CPU if it is data or an instruction, since the CPU has no way of knowing. |
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What is a database?
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A persistent organised store of data. |
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Explain the use of data handling software to create, maintain, and interrogate a database. |
Most database systems are handled by a database management system. This software handles the data directly and provides an interface to the applications. It can separate application programs from the data. |
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Describe how a DBMS allows the separation of data from applications and why this is desirable. |
It prevents applications from conflicting with each other and compromising the integrity of the database. Programmers who write applications do not handle the data directly, but have to work through the DBMS. |
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How can a DBMS be used to create customised data handling applications? |
It allows different applications to access the data at the same time. It controls access to the data with security features. It provides backups and the ability to restore from a backup. It supports query language and other languages which can extract, add, and amend data. New applications can be written using supported languages. It can force referential integrity, this means it prevents operation that could damage the relationships. It controls concurrency, so it locks the data when someone is working on it so no one else may change it at the same time. |
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Understand the relationship between entities and tables. |
A relational database stores data in tables. Each table contains data about just one entity. A table is called a relation. |
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What are tables? |
Tables have attributes, arranged in columns. A single instance of an attribute is a field. A table has rows, equivalent to records. Tables must have a primary key, so each row must be uniquely identifiable. Each row has the same data structure. Tables are linked by primary and foreign keys. |
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What are forms? |
The average user doesn't want to use SQL queries to find or change data. On-screen forms are provided so the information is easy to see and modify. They are user friendly and sit on top of hidden program code that does the work of finding or changing data. |
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What are queries? |
Queries are objects that extract data from a database. They are used to select the fields required and the conditions that need to be met. |
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Learn SQL just in case. |
Okay. |
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What are reports? |
These are often printed output of data from the database. They can be tables of data or fully formatted and well presented reports for management. They are usually based on queries that have done the work of extracting and collating the fields required. |
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What are modules? |
Database software and languages contain modules, which are pre-written programs. You can edit modules in the programming language and your own procedures. |
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Explain the use of key fields to connect tables and avoid data redundancy. |
Tables can be connected with primary and foreign keys. Primary keys must be a unique value. Compound primary keys are made from more than one field. Primary keys are often used to link a table to a foreign key in a different table. A foreign key doesn't have to be unique. This allows data for something to be held just once. |
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Describe methods of validating data as it is input. |
Validation is the process where data is checked as it is entered into a system done by the data handling software. For example: Check digit - When data is entered, the calculation is repeated and if the same check digit is not generated, the input is rejected. Common in bar codes. Format check - The data might have to conform to a particular pattern. For example, the UK car registration numbers are in the format LLNNLLL. Length check - The data must be within certain digits. A phone number could be set up to be no longer than 12 digits. Lookup check - Some fields might be looked up to see if they are from an allowed range. Postcodes could be checked to see if they exist. Presence check - This is to ensure all important information has been included in something like an application. Range check - A number must fall within limits. Type check - The data type might be restricted. For example, no numbers allowed in a name field. |
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Explain the advantages of networking stand-alone computers into a local network area. |
They allow groups of users to share and exchange information very easily. Networks bring people and data together, which improves productivity. Groups of users can send data to each other over networks. Centralised databases are made possible. It is possible to hold data and software anywhere so it does not need to be installed in each machine. |
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What is a network interface card? |
The circuitry that prepares and generates the signals presented to the carrier medium on a network. |
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What is a termiantor? |
A device attached to the end of a bus network to prevent signals from bouncing. |
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What is a repeater? |
Any signal transmitted along a medium will weaken. A repeater cleans up a message and sends it to the next segment. |
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What is a hub? |
Hubs are effectively repeaters but have more than one output port. They can boost a signal and then sent it onto all the devices connected to the output ports. Only the intended receiver of the data will process it. |
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What are bridges? |
Devices that connect different segments as well as different media. They operate on data packets and send them to the right segments. |
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What are switches? |
A switch is a high speed bridge. It is high speed since it has a dedicated CPU designed purely to perform switching operations. A bridge has a general purpose CPU and uses it to route packets to segments. |
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Explain the different roles of computers in a client-server network. |
One or more computers are designated as servers. These provide services to the rest of the machines in the network, known as the clients.
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Explain the advantages of a client-server network. |
Central control of security Easier to supervise network performance Easier to perform software upgrades Faster performance because of fewer data collisions Client machines freed up to perform their jobs Easier to perform backups |
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Explain the disadvantages of a client-server network. |
A knowledgeable admin is needed Only the admin can set up access and enforce security rules The admin has enough work to do to justify paying someone else to carry out that role There is more infrastructure to be set up with wiring cabinets and building work may be necessary If a server malfunctions it will have more impact on work than in one peer is lost on a peer-to-peer network |
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Explain the different roles of computers in a peer-to-peer network.
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In a peer-to-peer network, all computers are equal. Every user is a network administrator and has to control their own machine. Access can be given to anyone else on the network. There are no restrictions on how the network is organised. It will often make use of a hub to connect computers. |
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Explain the disadvantages of a peer-to-peer network. |
No network-wide security is in place - security is up to each user They soon become unworkable because the users have too much to worry about A machine slows down when being accessed by another A user might restart a machine when someone else is accessing it It is difficult to keep track of who has what information Backup becomes complicated |
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Describe the ring topology. |
The devices are arranged in a circle. Each computer is responsible for passing the message on. A ring topology guarantees that a computer can send a message since there's no need to wait. |
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Describe the bus topology. |
A bus network has a single backbone cable and all the devices are attached to it. When a message is sent it is divided into chunks and sent both directions along the cable. All computers receive it, only the one addressed accepts it. Only one computer can transmit at a time, they need to wait if the network's busy. Terminators are at the end to stop bouncing. |
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Describe the star topology. |
The most common way to set up a network. All connections are to a central device such as a wiring cabinet with switches. Installation is labour intensive and cables have to go through walls and ceilings or under floors. The network performance is faster than a bus. If one part of the network is damaged it does not necessarily affect the entire network. |
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What is the difference between a local area network and a wide area network such as the internet? |
LAN - Local area network. A LAN is located at one site. The site might be one building or several buildings. The infrastructure is owned by the organisation that uses the network, the cabling and hardware are the owner's responsibility. WAN - Wide area network. Made from widely spread LANs connected together. The different parts of the WAN are connected by telecom companies who own the infrastructure and charge for use. MAN - Metropolitan area network. It covers a wide area such as a city. PAN - Personal area network. Set up by one or a few individuals to connect a range of devices. |
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What is IP addressing? |
Each computer on a TCP/IP network has an IP address, which is a 32-bit numerical identifier. IP addresses are allocated to a device which allows switches to locate a resource on a network by its IP address. |
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What is MAC addressing? |
MAC stands for Media Access Control. Each physical interface connected to a network has a unique number written to the device. The MAC address is used to identify a device on a network. |
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What are packets? |
The internet is a packet switching network. This means that data is sent as bundles of data called packets. |
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What are protocols? |
Protocols are the rules used for devices to communicate. It is important to have a common protocol for the internet.
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Why do we need security measures in networks? |
Organisations depend so much on their networks so it is important that they are protected against failure or malicious acts. Users must enter a user ID and password, which must be suitable. The ID determines what level of access will be available. Traffic sent over a network is usually encrypted so that if it falls into the wrong hands, it won't be usable. |
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Describe and justify acceptable use policies. |
Human carelessness allows network security to be breached. To avoid this employees sign acceptable use policies which include things like: Use polite language online Not revealing personal details Not using the network for sending unsolicited mail Not sending offensive documents or images Not using the network for personal commercial purposes Not defaming anyone Not downloading programs |
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Describe and justify disaster recovery policies. |
Disasters, such as earthquakes and fires may happen. Most networks have recovery plans, which usually includes three elements: Prevention Detection Correction |
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Describe and justify failover. |
Failover is the process when software detects a problem in the system and the network switches to a duplicate system. |
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Describe and justify back up. |
Data is replicated off site and stored. |
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Describe and justify archiving. |
When data is no longer in regular use, it is copied and stored somewhere safe, just in case someone needs it one day. Then it is deleted from the working environment. |
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Describe the nature of the internet. |
A worldwide collection of computer networks. |
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Describe the hardware needed to connect to the internet. |
Modems are needed to transmit data to computers. Routers are needed in large networks. The routers ensure that information doesn't go where it's not needed and to make sure the information gets to the correct destination. |
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Why do we need IP addressing and how can it be facilitated by DNS services? |
IP addresses allow data to be sent to the right computers. Domain name servers translate website names into IP addresses. |
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Explain the importance of HTML and its derivatives as a standard for the creation of web pages. |
Uniform standards allow communication between devices of different specifications and from many different manufacturers. The world wide web has its own standards and HTML forms the basis of all web pages. |
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Explain the importance of compressing files that are transmitted via the internet. |
It is necessary to reduce download times for what might be very large files. |
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Describe the difference between lossy and lossless compression. |
Lossy compression involves removing some of the data from a file in order to reduce its size. Lossless compression is the opposite of this, for when information must be transmitted 100% correctly. |
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What is the difference between high level code and machine code? |
Machine code is the code the CPU uses when it decodes an instruction and is specific to the processor. High level code is closer to spoken language and does not have a one-to-one correspondence between the commands and the machine code and one high-level command may represent many machine code commands. |
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Why are translators needed to convert high level code to machine code? |
The computer can keep a list of what the codes are and labels for memory locations instead of the programmer having to do this themself. |
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Describe the characteristics of an assembler. |
Machine code is in binary, the list of commands available in mnemonic form is called the assembly language and the program to convert the mnemonics to machine code is called an assembler. |
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Describe the characteristics of a compiler. |
The compiler converts all of the high-level source code to machine level object code before attempting to run the object code produced. |
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Describe the characteristics of an interpreter. |
The interpreter converts the source code one instruction at a time into machine code then runs it before translating the next instruction. |
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Describe common tools and facilities available in an IDE. |
The code editor provides a text editing area that helps to organise the code by managing the layout. The error diagnostics include an errors and warnings list to identify any problems in the code. The run time environment allows the developer to run the code during development. This can be used to check for logical errors or that the code does what it is expected to do. The translator compiles or interprets the source code into suitable machine code instructions that can be run on the computer The auto documentation feature takes note of all the variables, modules, subroutines and comments as the project is developed and tidies this up into a text file. |
