Computing Theory

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  • Created on: 01-06-13 13:49
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1
CG1.1
Processor:
ALU - performs the calculations on the data.
Control Unit - controls all of the operations inside the computer.
Register ­ stores a single item of data.
Memory:
RAM - is the type of memory used for temporarily storing programs and data.
· Volatile ­ the data is lost when the power switched off
ROM - is used for storing permanent data.
· Non-volatile ­ the data is never lost
· Uses: Stores bootstrapping program\ embedded systems
RAM Cache ­ used to temporarily store frequently used data
· Faster than RAM\ Speeds up Computer
Buses:
1. Data Bus ­ carries data from the processor to different parts of the computer.
2. Address Bus ­ carries the memory location of data to be stored in RAM.
3. Control Bus ­ carries control signals from the control unit to other parts of the computer.
Bit: a single binary digit. 0 or 1
Byte: a group of 8 binary digits.
Word: is the number of bits that the CPU can handle at a time.
Secondary Storage:
Disk Cache - stores data when it is input from a disc for faster access.
Web Cache ­ stored data of frequently used webpages for faster access.
Magnetic tape
o Access: Sequential\ Slow
o Storage: Very large
o Cost: Very cheap
o Portability: Good\ Durable
o Use: Large back ups
Magnetic disk
o Access: Direct\ Fast
o Storage: Large
o Cost: Reasonably cheap
o Portability: only as an external hard drive
o Use: Computer hard drive
Optical disk (CD-ROM ; DVD)
o Access: Direct\ Fast
o Storage: Small to medium
o Cost: Cheap
o Portability: very portable but some durability issues
o Use: Software install disks
Flash memory
o Access: Direct\ Very fast
o Storage: Small to medium
o Cost: Quite expensive

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Portability: very portable due to size
o Use: portable data transfer
Analogue\ Digital:
1. Difference - analogue is a continuous varying signal and digital consists of discrete bit patterns
2. Computers are digital and analogue signals such as temperature\ voice need converting
to digital for processing
Hand Shaking - A signal sent from one device to another. Acknowledges devices are ready to
communicate.…read more

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VoIP (Voice over Internet Protocol) - used for sending voiced messages over the Internet.
WAP (Wireless Application Protocol) - enables the transmission of data over a wireless network.
Wireless Networks:
Hardware ­ Wireless Router\ Wireless network card
Advantages:
No need for cabling.
Computers can be used anywhere within range of the signal.
Disadvantages:
Data transmission speeds can be slow.
Data signals can only be received within a limited range.…read more

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A new master file is created and copied across
3. Data that needs updating is updated from transaction to master file
4. New master file replaces the old master file
Verification:
ensure data is consistent
ensure data have not been corrupted
Carried out when d_ata is being entered or transferred
Types:
Screen verification: A visual check by eye that no errors have been made.
Example: proof-reading work submitted.
Double-keying: This is a check to see if data has been keyed in correctly.…read more

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Data can be accessed speedily and manipulated to form new data
A single database can be shared, internationally if need be
Data duplication can be avoided
Security of data can be centralised
Disadvantages:
Centralised data can be easier to steal than decentralised data
If data is not correct, it filters through to all users of the data
CG1.…read more

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Variable: A name used to refer to a memory location used to store data. The value can be changed
when the program running.
Global Variable:
Declared at the beginning of the program and is available throughout the code, including all
subroutines.
Local Variable:
Declared and used inside only one subroutine. It is created and destroyed when the subroutine
exits.
Sequence:
A set of instructions are executed once in the order written.
Selection:
Different options are decided upon based on a condition. Not all are executed.…read more

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· Initialising Variables
· Annotation
Levels of Languages:
Machine Code
1. Consists of a series of zeroes and ones to make up both instructions and data.
2. Processed by all computers,
3. Very difficult for people to learn
4. Prone to difficult-to-detect errors
Assembly Language
1. One assembly language instruction translates to one machine code instruction.
2. Great deal of skill to program
3. More flexibility in the applications that can be created.
High-level Languages
1.…read more

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Advantages
1. It is much faster to send a message (seconds instead of days)
2. It is cheaper - there are no extra charges for sending emails
3. One message can be sent to a number of people.
4. You can send 'attachments' - pictures; sounds; video clips etc
5. It does not matter if the recipient is on-line when the email is sent.
Disadvantages
1. you cannot send physical objects - eg a parcel
2. a large volume of emails are unwanted 'spam'.…read more

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Example: Pay roll system ­ All hours worked are stored up and processed at the end of the
month
Example: Electricity bill system ­All the meter readings from premises that use electricity are
collected together and processed as a batch.
Real Time Processing:
1. data received by the computer is immediately processed
2. stored data is updated and any necessary actions taken.
3. The computer used in a real-time system is dedicated - it does nothing else.
Example: Controlling temperature in an industrial process.…read more

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Direct ­ Changing over to new one immediately
Advantage: Not very costly
Disadvantage: Could be disastrous if there are errors in the new system
Parallel ­ Running both systems together until no issues
Advantage: no disasters if there are errors in the new system
Disadvantage: a lot of duplication of work
Piloting ­ Trying out system in small area of company
Advantage: Problems will only impact pilot area.…read more

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