Computing Notes f451

Not organised, detailed

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  • Created by: Jenny Lea
  • Created on: 13-05-12 11:32
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Exam technique
Lots of 3 mark questions
2 marks ­ A
1 mark - E
UNIT 1: Components of computer system
Physical parts of a system
You can actually touch it and smash it
Printer, monitor, mouse
Electrical/electronic components
Electromechanical components
Disk drives
Mechanical components
Peripheral devices
Outside the computer processor
Connected by cables
E.g. printer/hard disk
Input, output, storage
Make machine produce useful results
Sets of instructions that tell the computer to do things
Instructions collected into workable groups called programs
Without programs computers couldn't function as they wouldn't know what to do
Word processor, spreadsheet, database
Systems software
Set of instructions that make hardware usable

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Keep a computer running
Allow human beings to communicate with the computer
Control movement of data around the computer
Allows software and hardware to communicate
Operating system (OS)
Applications packages
Designed for a particular task
Word processor, presentation software
Sends data to the computer
Converts electrical signals representing data into a form that can exist outside the computer
Piece of hardware that receives data from the computer
Maintain records that can be accessed and edited at another time
Stored outside the processor…read more

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Fail to fully understand business opportunities
Difficulties arising
Organisational factors ignored
Jobs of individual users may be ignored/have to be changed
Aims of systems life cycle
Thoroughly understand goals
Formal procedures and methods
On time delivery to required specification
UNIT 3: Binary, Hex
Base 2
1s and 0s
128 64 32 16 8 4 2 1
The highest you can get is 255
8 bits of binary in one byte
2 (denary) = 10
10 (denary) = 1010
Half a byte (4 bits)…read more

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Subtracting binary
Like long subtraction
Use two's complement then add the minus so it's like taking the number away
UNIT 4: CPU Architecture
Control unit
Organises everything
Fast but slowed down by memory
Memory unit
Stores information
ALU does calculation and passes it on to memory unit
Speeds of CPU clapping
Electrical pulse
Arithmetic logic unit
Does the arithmetic
Does the logic
Handles numerical mathematical functions
Deals with non-numerical logic operations
And or not
Boolean values…read more

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And makes use of two separate statements only when both apply
Both inputs have to be true
Or makes use of two statements when only one needs to apply
Only one input has to be true
Boolean logic ­ only two states
Operator ­ thing that makes it do stuff
Connection of wires in parallel to transmit information
Low level ­ not as smart
First click ­ CPU specifies
Second click ­ Memory gets file
Third click ­ Memory sends it back (if needed)…read more

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Quick to write data to
Save before turning computer off saves to hard disk and makes it none volatile so you won't lose it if the
computer goes off
Store numbers whilst doing a calculation
-R discs
Writeable, not rewriteable
+R discs
ROM read only memory
Put on by the manufacturer and you can't change it
Non rewriteable CD
Helpful as people can't edit/break it
Computer will work
"Burnt into the memory"
Computer knows how do work stuff when turned on
Lots…read more

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Doesn't take long to give you your stuff
Can't change or update it
Backing store/secondary store
Hard disk
Slow but cheap
Closer memory > secondary storage
Secondary storage is cheaper
Closer memory is more expensive
Do spontaneous things
RAM is volatile
If you cut the power you lose what was stored
Data bus
Sends data from CPU to write to memory
Sends data from memory to CPU on request
All sent in binary/ASCII in binary
Keyboard connected to data bus
Address bus…read more

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Local store of memory
More expensive than other memory
An store less than other memory (depending on cache size)
Quicker access
Memory bus takes time
For things you know will be used regularly
L1 cache
If needed quickly
Notepad right in front of you
L2 cache
If needed not quite so quickly
Book on desk
Takes longer to access
Miss Morris in the library
Magnetic discs
Concentric "tracks" split into "sectors"
Looks like old fashioned record player
Hard disk is a magnetic disk…read more

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There are better ways of doing it
Still being used today
Hard drive disk
Needle reads disk
More precise
Multiple disks increase capacity
Very common
Flash storage
Do not call USB sticks
Can call memory sticks
The whole things fit into
Flash storage
Bluetooth dongles
Printer is miles slower than CPU
If writer goes slower you will be there for ages
Store data when there is a speed mismatch between computers/processors
E.g.…read more

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Computers RUN or EXECUTE programs
In order to execute a program it must be stored in the computer memory
It must occupy a set of consecutive bytes
Be written in the computer's specific internal machine language
Each CPU has its own internal machine language
Program has to be rewritten to be executed on another CPU
Program stored in computer memory IMPORTANT CONCEPT
If you change the program stored in memory the computer can carry out a completely different task
"Stored program concept"
Instructions are split…read more


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