Computer Science Theory

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How do computers store data?
Binary
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What way to humans use numbers?
Denary
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What is another way to present numbers other than binary and denary?
Hexidecimal
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Why would numbers be saved in hexidecimal?
The binary number is very big; so in order to use less memory
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How many bits is one byte?
8
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How much memory does an integer use?
4 bytes
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How much memory does a float use?
8 bytes
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How much memory does a character use?
1 byte per character
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How much memory does a boolean use?
1 byte
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When comparing types of memory, what should you consider?
Speed of accessing files to read and/or write, price, and volatility
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What is RAM?
Random Access Memory
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Where is RAM used?
Main memory
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What kind of storage is RAM
Temporary and volitile
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Define volitile
Loses its contents when the device is turned off
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Where does the computer get it's basic start up rountine, OS and programs?
Somewhere non-volatile such as hard disk
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Why doesn't the processor get instructions from the disk?
Reading and writing to it is very slow
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Without RAM, a computer would be...
...very slow
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What software loads the OS?
Bootstrap loader
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What is ROM?
Read Only Memory
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Can you change read-only memory once it has been changed?
No
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What is the volatility of ROM
Non-volatile
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Where is every running program stored?
Main memory
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If lots of programs are running then...
..lots of main memory is needed
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If the computer doesn't have enough main memory...
...part of the hard disk can be onfigured to act like main memory
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What is Virtual Memory?
The part of the hard disk that has been configured to be like main memory
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What is faster: RAM or Virtual Memory?
RAM
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What can be stored in Virtual Memory?
Running programs
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What cannot be stored in Vitual Memory?
Parts of the program being executed
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Explain how instructions from a program stored in Virtual Memory can be executed
Parts of the programs are swapped between VIrtual Memory and RAM so parts can be executed
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Main memory is...
...Primary memory
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What are the characteristics of Secondary memory?
Long term, non-volatile, cheap, very large, robust, reliable
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Examples of Secondary memory
Memory sticks, floppy disks, tape, CDs
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Does Main memory or Secondary memory have the faster access speed?
Main memory
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When choosing a storage medium, what should you consider?
Reliability, Durability, Portability, Speed (to read and write data), capacity/storage space
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Give examples of magnetic storage media
Tape, hard disk, floppy disk
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How is data saved on magnetic storage media?
The actuator moves the write head to the correct place on the medium. the write head creates a magnetic field, this magnetises dots on the magnetic material in binary patterns, storing the data
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How is data read from magnetic storage media?
The actuator moves the read head to the correct place. the head then is able to detect the magnetic field and read the binary
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Advantages of magnetic storage media
Cheap, high capacity
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Disadvantages of magnetic storage media
Slow to read and write to, easily wiped/damaged (due to moving parts)
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Give examples of optical storage media
CD and DVD
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How is data stored on optical storage media?
A laser inside the computer marks the disk's surface with dots and dashes that represent binary's 1s and 0s
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How is data read from optical media storage?
Light is reflected of the shiny surface of the disk so it can detect the dots and dashes
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Examples of uses of flash storage media
Memory stick, in phones, tablets, PCs and cameras
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Advantages of flash storage media
Very fast access speed, reliable (due to no moving parts), good replacement to hard disk, robust, uses less power
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Disadvantages of flash storage media
Can't replace main memory (access speed too slow)
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How is data saved and read from flash storage media
The flash storage media has a chipp called an EEPROM which contains lots of tiny switches. An electrical current sets to switches to 1 or 0 which can save data. the computer reads the binary to read the data
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Define algorithm
A set of instructions followedby a computer or program in order to carra out a particular task
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Define pseudocode
Universal, non-language specific, code that is used to plan the code of a program
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Give advantages of splitting a program into modules to be developed
Different parts can be code by different people at the same time, repeated parts of code can be re-used more easily, modules can be tested induvidually, the task is easier to maintain and understand
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What is the advantage of testing modules individually?
Bugs can be found and fixed more easily
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What are the types of error?
Syntax, Run-time, and Logic
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What is a syntax error?
An error caused by an error in the code
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What causes a syntax error?
Typos, and opening, but not clsoing brackets of speech marks
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What is a logic error?
An error that occurs when the program successfully runs but doesn't do what is expected
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What causes a logic error?
Missing brackets (remember BIDMAS applies), loop that haven't been iterated the correct number of times etc
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How do you find a logic error?
Using a trace table
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How does a trace table work?
Variables are recorded in a table as the algorithm is executed line by line
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How do you fill in a trace table?
By writing down variable as they change. If they do not change, they are not written
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What is a run-time error?
An error that causes the program to crash
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What causes a run-time error?
User inputs in an unexpected data type, trying to open a file that doesn't exist, if the computer has run out of memory, and if the program tries to read from an empty file
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What is checked during the Feasibility stage of development
Technical, economic, legal, operational, and schedule feasibility (TELOS)
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What is technical feasibility?
Checking if the technology exists to be able to do what you want
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What is economical feasibility?
Checking if the project if worth the money
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What is legal feasibility?
Checking if the project would have any copyright or licensing issues
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What is operational feasibility?
Checking if the user will be able to operate the program
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What is schedule feasibility?
Checking if it is possible to develop the softeare in the timescale
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What is done during the Analysis stage of development?
Data is gathered about the project through interviews and questionnaires to create a specification and user requirements
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What is done during the Design stage of development?
Flow charts, pseudocode are produced of the main algorithms to show how data will be processed, and details of HOW the program will be tested are decided
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What is done duting the Implementation stage of development?
The program is coded, tested and installed
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What is done during the Evaluation stage of development?
Checking the software against the original specification and user requirements
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What is done during the Maintainence stage of development?
The software is maintained and updated while it is in use to fix problems found by users
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What are the three types of maintainence?
Corrective, adaptive and perfective maintainence (CAP)
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What is corrective maintainence?
FIxing problems that were not found in testing
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What adaptive maintainence?
Updating the software to fit changing user requirements
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What is perfective maintainence?
Cosmetic improvements to change the way the software looks
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Advantages of the Waterfall model
Self contained, easy to manage stages; defined output and processes per stage; good for managing large groups of developers working in parallel
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Disadvantages of the Waterfall model
Requirement changes means going back to previous stages;changes can be costly in both time and money; lack of customer involvement means issues aren't found until evaluation
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Advantages of the Cyclic model
Self contained, easy to manage stages; defined output and processes per stage; good for managing large groups of developers working in parallel
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Disadvantages of the Cyclic model
Requirement changes means going back to previous stages;changes can be costly in both time and money; lack of customer involvement means issues aren't found until evaluation
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Advantages of the Spiral model
Well defined, managable stages; prototypes highlight issue quickly; changes can happen easily
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Disadvantages of the Spiral model
Takes a long time, and more time means more money; prototypes are expensive to create
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Advantages of the Agile model
Well defined, managable stages; prototypes highlight issue quickly; changes can happen easily; small multitasking groups make the team flexible to changing requirements
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Disadvantages of the Agile model
Takes a long time, and more time means more money; prototypes are expensive to create; only suitable for smaller development teams
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What is a prototype?
An approximation of the finished piece; a model, sample
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Advantages of prototyping
Customers can give feedback, the developer can get useful feedback before it is too late, the product can be changed during development
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Disadvantages of prototyping
Expensive, time consuming, if the customer keeps changing what they want it takes even longer
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What are methods of testing?
Tracing algorithms, module testing, integration testing, peer review, beta testing, and acceptive testing
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What is alogrithm testing?
Using a trace table to record changing variables
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What is module testing?
Testing modules individually
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What is integration testing?
Testing modules together
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What is peer review?
When collegues test the software
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What is beta testing?
Testing the software on a small group of potential users
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What is acceptance testing?
When the developer goes through a test plan to prove to the customer that the software works
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What is computer hardware?
The physical components of the computer
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What is computer software?
The programs that run on a computer
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Examples of computer input devices
Mouse, keyboard, camera, microphone, touchscreen etc
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Example of computer output devices
Monitor, speakers etc
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What is a peripheral device
A computer device that is not an essential part of the computer
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Examples of peripheral devices
Printers, scanners etc
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How do you measure reliabilty of a system?
System availability OR mean time between failure (mbtf)
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How do you calculate system availability?
Number of hours available out of 100 as a percentage (ie. If a system was down for 1/100 hours, its reliability is 99%)
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What is robustness?
How tolerant a system is to failure
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What is the CPU and where is it?
The CPU is in the hardware that executes programs and manages the rest of the hardware
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What is the fetch-execute cycle?
(After the program is loaded into main memory...) An instruction is fetched from the main memory, it is decoded, it is executed. This is repeated
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What is the CPU made up of?
Main memory, the processor, and cache
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How does data move between main memory and the processor?
On internal connections called system buses
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What is the purpose of the CPU?
To fetch data and instruction from main memory, to decode and execute instructions, to perform calculations, to manage the movement of instructions and data to and from peripheral devices
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What is clock speed?
The speed at which a processor operates measure in electrical cycles per second (Hertz)
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How does cache memory/RAM speed up a computer?
The the less often the processor has to access the main memory, the faster it can work. Cache/RAM is small amount of much faster memory that is used to store frequently used instructions and data so the speed of the computer is improved
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How many levels of cache are there?
3
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Describe Level 1 cache
Built on to the processor chip, fastest type of cache, most expensive, stores most critical data and instructions
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Where is Level 2 cache?
On the motherboard or processor chip
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Where is Level 3 cache?
If Level 2 cache is on the processor chip, L3 cache is on the motherboard
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What effect does having a multi-core processor have on the speed of the CPU?
More processors means the computer is faster
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Why is a dual core processor only twice as fast IN THEORY?
It would only be faster if the computer has different programs running parallel becuase then a different core does each program
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Where are the system buses found?
On the motehrboard
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How many system buses are there?
3
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What are the names of the system buses?
Address bus, Control bus and Data bus
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Which bus is used during the "fetch" part of the fetch-execute cycle?
Address bus
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How many directions can information travel along the address bus?
One way
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Which bus is used to send instructions from its place in memory, to the processor?
Data bus
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How many directions candata travel along the data bus?
Two ways: data can be sent from memory to the processor, and, in the opposite direction, data can be sent back to main memory or secondary storage
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How many components can use the bus at once?
Only one
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What is the purpose of the Control bus?
It carries signals that show if the data and address buses are free
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What is a relational database?
A database that uses separate tables that are related so there is no data duplication
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Advantages of less data duplication
Less risk of data inconsistency, easy to maintain database, makes the database smaller
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Define table
A collection of data about a specific entity eg. Movies
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Define record
All the information about one thing eg. Genre, Cast, Rating
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Define primary key
The field that uniquely identifies each record in a table eg. Movie ID
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Define field
Each data item in a record eg. The genre of film ID0023
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What does a query do?
Search a database using a search criteria to find particular records
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What is a LAN?
Local Area Network: A collection of computers and peripheral devices connected together within a single site (NOTE: site not building)
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What is a WAN?
Wide Area Network: A collection of computers, peripheral devices, and networks connected over a geographically remote area (NOTE: Geographically remote doesn't mean the networks are miles apart, it's about what separates the sites such as a road)
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What kind of network is the internet?
WAN
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Advantages of networking computers
Sharing resources, communication between computers, and centralised management
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What resources can be shared over a network?
Files, peripheral devices, an internet connection
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How can computers communicate over a network?
Emails, a messaging system, and by transfering files between computers
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How does a network use centralised management?
User profiles and security are managed centrally; softeware can be distributed across the network rather than to each individual PC, and users are able to access their files from any PC on the network
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What is a network topology?
The different layouts for which computers in a network can be connected
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How does the ring network work?
Computers are connected to those next to them in a ring. Each computer takes turns to transmit, controlled by passing around a tocken. Only the computer with the token can transmit. Used in LANs
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Advantages of the ring network
Not dependant on a central computer, token passing protocol is simple and therefore reliable, consistent performance even with high traffic
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Disadvantages of the ring network
One link failure could disrupt the whole network, not secure because all connections are shared, all data goes around the network so it's slow
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How does a bus network work?
All computers are connected to a single backbone cable that computers use to transmit; only one computer can transmit at a time. Used in LANs only
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Advantages of the bus network
Easy and inexpensive to install, easy to add new computers, transmitting onto a bus is quicker than sending data around the network
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Disadvantage of the bus network
If the main cable fails, the whole network goes down; cable failure are hard to isolate as they affect the attached computers; not secure; slow when there is traffic
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How does a star network work?
Each computer is connected to a central hub which controls the network. this is usually a server where all files are saved. Used for LANs and WANs
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Advantages of the star network
One failure will only affect one computer, consistant performance, easy to add new computers, more sercure becuase links aren't shared
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Disadvantages of the star network
Can be costly becuase there is lots of cabling, dependance on central switch so if it goes down the whole system does
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How does a client-server network architechture work?
Every user's files are saved on the central server so they can be access from every PC in the network. Used in a WAN
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How does the peer-to-peer network architechture work?
The user's files and documents are saved on the individual PC but are configured to share them with the other PCs on the network if access has been granted. All computers have equal status. Used over a small LAN
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Which network architechture has computers all of equal status?
Peer-to-peer
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Which network architechture has computers with specialised roles?
Client-server
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Which network architechture is easy to set up and maintain?
Peer-to-peer
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Which network architechture needs a network manage to run the network?
Client-server
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Which network architechture has no centralised management?
Peer-to-peer
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Which network architechture has centralised management?
Client-server
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Which network architechture has no dependancy on a server?
Peer-to-peer
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Which network architechture has dependancy on a server?
Client-server
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Which network architechture is only used in LANs?
Peer-to-peer
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Which network architechture is used in WANs and LANs?
Client-server
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Which network architechture is used for a small group of computers (10 or less)?
Peer-to-peer
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Which network architechture can be used for hundreds of computers?
Client-server
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What is between the client and server?
Their internet connection
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Other cards in this set

Card 2

Front

What way to humans use numbers?

Back

Denary

Card 3

Front

What is another way to present numbers other than binary and denary?

Back

Preview of the front of card 3

Card 4

Front

Why would numbers be saved in hexidecimal?

Back

Preview of the front of card 4

Card 5

Front

How many bits is one byte?

Back

Preview of the front of card 5
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Comments

nerdwow

Wow this really good

swifty017

Very good enjoy revising from this

Basital

Thank you. This is very useful for revision!

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