Cambridge IGCSE Computer Science
0948/0478 syllabus for 2023, 2024 and
2025
what is a character set - ANS A representation of characters as numbers. Each character gets a number.
Unicode and ASCII are character sets.
what is ASCII code - ANS American Standard Code for Information Interchange - it is used to represent
the english alphabet and encodes 128 characters into 7-bit binary codes
What is Unicode? - ANS Unicode is used for internal representation of characters and strings and it uses
16 bits to represent each other.
what are the 2 differences between ASCII code and unicode - ANS - unicode allows for a greater range of
characters including different languages than ASCII
- unicode requires more bits per character than ASCII
how does a computer represent sound - ANS a sound wave is sampled so it can be stored and processed
by a computer
What is sampling? - ANS when an analogue to digital converter converts sound into a digital form
what is the sample rate - ANS the number of sample taken in a second
what is the sample resolution - ANS Number of bits per sample
what happens as the sample rate and resolution increases - ANS the accuracy of the recording and the
file size increases
,What is an image? - ANS An image is a series of pixels that are converted to binary, which is processed
by a computer
what is the resolution of an image - ANS the number of pixels in the image
what us the colour depth of an image - ANS the number of bits used to represent each colour
what happens as resolution and colour depth increases - ANS the file size and quality of the image
increases
how do you calculate file size of an image file - ANS resolution (width x height) x bit depth
how do you calculate file size of a sound file - ANS sampling frequency x bit depth x length
what are 3 advantages of compression - ANS - less bandwidth required
- less storage space required
- shorter transmission time
what is lossy compression - ANS Compression in which some of the information is permanently
removed. e.g. reducing resolution, colour depth or reducing sample rate
what is lossless compression - ANS Making the size of a file smaller without permenantly losing any of
the information in the file.
what happens to data to be transmitted - ANS data is broken down into packets to be transmitted
, what is the structure of a data packet - ANS a data packet contains a packet header a payload and a
trailer
What is a payload? - ANS the actual data being sent
what is a trailer - ANS the end bit of a data being sent
what is the packet header - ANS a packet header includes
- destination address
- packet number
- originators address
What is packet switching? - ANS a mode of data transmission in which a message is broken into a
number of packets that are sent independently, over whatever route is optimum for each packet, and
reassembled at the destination.
what is serial data transmission - ANS where bits are sent one signal at a time over a single wire allowing
high data transfer rates to be achieved
what is parallel data transmission - ANS where bits are sent simultaneously over a number of parallel
wires
what is simplex data transmission - ANS Data is sent in one direction only
What is half-duplex transmission? - ANS where data can travel in both directions along a single cable but
not simultaneously
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