Cambridge IGCSE and O Level Computer Science Second Edition
These are notes which cover the whole Cambridge IGCSE computer science syllabus. They have been made from a variety of sources to ensure you can understand. It is enough to make you ready for exams.
Detailed flash cards for Computer Science, 0478 ( Full syllabus covered )
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o 1-Data representation
Number systems
Why is the binary number system used for computers→This is
because data is processed in a computer by the use of logic gates
which have only 2 states, ( 1 and 0)
What is the hexadecimal number system→This is a base 16
number system that uses the values 0-9 and A-F.
What are the advantages of hexadecimal compared to binary for a
programmer
Hexadecimal is a shorter way of representing binary, hence
it takes up less screen space
Hexadecimal is easier for a programmer to read, write and
understand
Hexadecimal is easier to debug and locate errors in data
What are the different uses of the hexadecimal number system
Error codes―these numbers usually refer to the memory
location of the error
MAC addresses
IPv6 addresses
HTML colour codes―Colour codes are always 6
hexadecimal digits and different hexadecimal values
represent different colours.
What is an overflow error→This is whereby the result of carrying
a calculation is too large for the computer's allocated word size
( e.g. an 8-bit register can only hold 8 bits not more )
What is a logical shift→This is an operation that shifts a bit to the
right(dividing it ) or to the left( multiplying it) in a register.
This is how you write it if there is an error in shifting
What is two's complement→This is a method of representing
negative numbers in binary. ( range of values that can be
represented is -128 to +127)
Text, sound and images
Metadata→This is the additional data that is stored with an image
that can provide information such as the dimensions of the image
and the time and date the image was taken.
, What is the ASCII code system→This is a character set for all the
characters on a standard keyboard and control codes which
consists of 7-bit codes ( 0 - 127 in denary )
The Extended ASCII uses 8-bit codes to allow for characters in
non-English alphabets and for some graphical characters to be
included
What is a character set→A list of characters that the computer
recognises and supports. It contains unique binary numbers for
each character and is necessary so that the computer can
understand human characters.
What are the disadvantages of the ASCII code
It does not represent characters in non-Western languages
What is Unicode→This is a character set which represents all of
the languages in the world. Unicodes use of up to 4 bytes per
character
Just in case→
Representation of sound
, What is sampling→This means measuring the amplitude of
the sound wave. This is done using an analogue to digital
converter
How is the sound converted from analogue to digital→The
sound waves are sampled at regular intervals, and since the
amplitude cannot be measured precisely, approximate
values are stored
What is the sampling resolution→These are the number of
bits that are used to record each sample ( the higher the
number of possible values used to represent the sound
sample, the higher the accuracy of the sampled sound )
What is the sampling rate→These are the number of sound
samples taken per second
What are the benefits and draw backs of using a higher
sampling resolution
Benefits―Large dynamic range
Better sound quality
Less sound distortion
Drawbacks―Produces larger file size
Takes longer to transmit/download
music files
Requires greater processing power
How is the filesize of a sound file calculated
sample rate ( in Hz ) x sample resolution ( in bits )
x length of sample ( in seconds )
IF IT IS A STERIO SOUND FILE, MULTIPY
THE RESULT BY 2
Representation of bitmap images
What is a bitmap image→This is an image made up of a 2-
dimensional array of pixels
What is colour depth→These are the number of bits used to
represent each colour.( If each pixel is represented by 2
bits, 2^2 number of colours can be represented )
What is image resolution→This refers to the number of
pixels that make up an image
What is a pixel→This is the smallest element used to make
up an image on a display
How is the filesize of an image calculated
, Image resolution ( in pixels ) x colour depth ( in
bits )
Data storage and file compression
o 2 - Data transmission
Types and modes of data transmission
Why is data broken down into packets when being sent→This is
because the wires or radio waves will not be able to accommodate
sending large amounts of data at a single time.
What is the packet structure and what does each of them contain
A packet header―IP address of the sender and receiver,
The sequence number of the packet, size of the packet in
bytes
The payload―The actual data
A trailer―Marks the end of the data packet, some form of
error checking to ensure the packet reaches error free Such
as Cyclic Redundancy Checks (CRCs)⇐ Adds up all one
bits and stores it as a hex value in the trailer.
What is packet switching→It is a method of data transmission
where a message is broken down into several data packets. Each
data packet can then be sent independently. Each stage in the route
contains nodes that contain a router, this router receives the data
packet, and based on the information in the header, decides where
to send it next. Once the data packets reaches its destination, they
will have to be reassembled into their correct order.
What factors need to be considered when transmitting data
What is serial data transmission→This is a whereby data is sent in
continuous stream with 1 bit being sent at a time over a single
communication line.
Better for longer distances however rate of transmission is slower
compared to parallel
What are the modes of data transmission
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