Notes for CAIE IGCSE Computer Science . Covering ( Data representation , Data transmission , Hardware ) Notes are not handwritten . Covers - Number system , Text sounds and images ,Data storage and file compression . Types of methods of Data transmission , Error detection . Computer architecture , ...
Binary shifts :
To multiply by two, all digits shift one place to the left
To multiply by four, all digits shift two place to the left
To multiply by eight, all digits shift Three place to the left
To divide by two , all digits one place to the right
To divide by four all digits shift two places to the right
To divide by eight , all digits shift three place to the right
Two's complement
Overflow occurs when a value cannot be represented in the number of bits allowed
Underflow occurs when a number is too small too small to be stored in the allocated number of bits, A number
is too small if it is too close to zero to be represented
Text
The ASCII character set is a 7 bit set of codes that allows 128 different characters, That is enough for every
upper-case letter, lower case letter, Digit punctuation mark on most keyboards. ASCII is only used for the
english language
Extended ASCII code is an 8 bit character set that represents 256 different characters, It is useful for European
languages.
Unicode uses 8 and 32 bits per character - giving billions of combinations - so it can represent characters from
languages from all around the world.It is commonly used around the internet.Unicode takes up more storage
space when saving documents. Companies like Facebook and google would use Unicode because their users
communicate in different languages
Sound
How is sound recorded? First sound is recorded using a device that can
Sound waves into an electrical signal . Then, Measurements of the level
Of the signal , called samples , are taken at regular intervals
The measurements are then converted into binary To convert the
Measurements into binary, a unique binary code is assigned to each
sample .After that, the digitised sound can be stored and processed by
a computer as a sequence of 1s and 0s.
Sample: Measurements of signal level of sound taken at regular intervals
Sampling rate is defined as the number of samples taken per second
It is measured in hertz, The higher the sampling rate the higher the
Quality of the audio recording
Sample resolution is the number of bits used to represent each sample the higher the sample resolution the
better the quality of the audio recording
To find the size of a sound file :
Sampling rate x Sample resolution x Seconds
This means that the size of a sound file will increase if the sampling rate, Sample resolution or duration of the
recording increases
Flowcharts
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