KEY:
Topic:
Definitions + Calculations + Theory Answers
QW: Question Word (e.g. Evaluate)
Long Method (e.g. 6 markers)
Calculations
Advantages and Disadvantages
Exam Practice Additions
COMPUTER SCIENCE
1.1 DR, Number Systems:
Computer system can only process data in binary because logic gates use only
1s and 0s.
Data is processed in logic gates and stored in registers.
Denary = base 10 system
Binary = base 2 system
Hexadecimal = base 16 system
Hexadecimal is used in memory dumps and URLs.
Hexadecimal is easier to understand, easier to debug and takes up less screen
space.
Logical shift error due to overflow, leftmost bits are lost so value becomes
incorrect.
Overflow occurs when there are too many bits for the register to store, registers
have a predetermined number of bits.
,1.2 DR, Text, Sound and Images:
Text is converted to binary to be processed by a computer.
Unicode allows for a greater range of characters than ASCII (including different
languages and emojis)
Unicode requires more bits per character than ASCII.
A character set is every character and symbol that can be represented by a
computer system. Each character and symbol is assigned a unique value.
Sound wave is converted from analogue to digital: Amplitude sampled at regular
intervals; each sample is stored as a binary number.
Sample resolution is the number of bits used to store each sample. Provides the
variation in amplitude that can be stored for each sample.
Sample rate is the number of samples stored per second.
The accuracy of the recording and file size increases as sample rate and
resolution increase.
An image is a series of pixels that are converted to binary, which is processed by
a computer.
Image resolution/pixel array is the number of pixels in an image, length * width.
Bit/colour depth is the number of bits used to represent each colour in a pixel.
Number of colours that can be represented. = 2n , n = bit depth.
The quality of the image and file size increases as the colour depth and
resolution increase.
,1.3 DR, Data Storage and Compression:
Kane’s Magical Goals Thrill People Everytime.
Bit, Byte, KiB, MiB, GiB, TiB, PiB.
Kibibyte, mebibyte, gibibyte, tebibyte, pebibyte, exbibyte
KB vs KiB = 1000 bytes vs 1024 bytes
8 bits in a byte
1024 mebibytes in a gibibyte
Sound file size: sample resolution * sample rate * length of recording
Image file size: image resolution * colour depth
Compression exists to reduce the size of a file.
Compression:
Less bandwidth required
Less storage space required
Shorter transmission time.
Lossless Compression:
A compression algorithm is used such as run-length encoding.
Patters in data are identified and indexed.
No data is permanently lost so can be restored to original format.
(Stores position of word/Number of times word appears.)
Lossy Compression:
Reducing resolution – fewer pixels per unit measurement, less binary to
store.
Reducing bit depth – fewer number of bits to represent each colour, each
pixel has fewer bits.
Data is permanently lost so cannot be restored to original format.
, 2.1 DT, Types and Methods of Data Transmission:
Packets contain:
Header- Sender’s IP address, Destination’s IP address, Packet number.
Payload.
Trailer – Marks end of packet, extra error checks.
Packet Switching:
Data is broken down into equally size fragment known as packets.
Each packet is assigned a packet number before transmission.
Packets take different routes to the destination.
Routers control the routes that the packets take, selecting the fastest
route available.
Packets may arrive out of order.
Once the last packet arrives, packets are reordered using their packet
numbers.
Series- cheap but slow, used in telephone line.
Parallel – fast but skewing and crosstalk, used in RAM and integrated circuits.
Simplex – cheap but slow, used in computer to printer
Half-duplex – cheaper than simplex for bidirectional but slow, used in walkie
talkies.
Full-duplex – fast but expensive, used in broadband connections.
Serial transmission used: Sent over long distances, One bit sent at a time across
one wires so will not skew, Crosstalk will not occur so less chance of errors.
Website uses parallel half duplex: Skewing not problem, not a long distance.
Parallel is the fastest transmission method for large amounts of data.
Advantages of USB: Backward compatible, cannot be inserted incorrectly, high-
speed transmission.
Disadvantages of USB: Maximum cable length is about 5 metres so cannot be
used over long distances, older versions have limited transmissions speeds.
Topic:
Definitions + Calculations + Theory Answers
QW: Question Word (e.g. Evaluate)
Long Method (e.g. 6 markers)
Calculations
Advantages and Disadvantages
Exam Practice Additions
COMPUTER SCIENCE
1.1 DR, Number Systems:
Computer system can only process data in binary because logic gates use only
1s and 0s.
Data is processed in logic gates and stored in registers.
Denary = base 10 system
Binary = base 2 system
Hexadecimal = base 16 system
Hexadecimal is used in memory dumps and URLs.
Hexadecimal is easier to understand, easier to debug and takes up less screen
space.
Logical shift error due to overflow, leftmost bits are lost so value becomes
incorrect.
Overflow occurs when there are too many bits for the register to store, registers
have a predetermined number of bits.
,1.2 DR, Text, Sound and Images:
Text is converted to binary to be processed by a computer.
Unicode allows for a greater range of characters than ASCII (including different
languages and emojis)
Unicode requires more bits per character than ASCII.
A character set is every character and symbol that can be represented by a
computer system. Each character and symbol is assigned a unique value.
Sound wave is converted from analogue to digital: Amplitude sampled at regular
intervals; each sample is stored as a binary number.
Sample resolution is the number of bits used to store each sample. Provides the
variation in amplitude that can be stored for each sample.
Sample rate is the number of samples stored per second.
The accuracy of the recording and file size increases as sample rate and
resolution increase.
An image is a series of pixels that are converted to binary, which is processed by
a computer.
Image resolution/pixel array is the number of pixels in an image, length * width.
Bit/colour depth is the number of bits used to represent each colour in a pixel.
Number of colours that can be represented. = 2n , n = bit depth.
The quality of the image and file size increases as the colour depth and
resolution increase.
,1.3 DR, Data Storage and Compression:
Kane’s Magical Goals Thrill People Everytime.
Bit, Byte, KiB, MiB, GiB, TiB, PiB.
Kibibyte, mebibyte, gibibyte, tebibyte, pebibyte, exbibyte
KB vs KiB = 1000 bytes vs 1024 bytes
8 bits in a byte
1024 mebibytes in a gibibyte
Sound file size: sample resolution * sample rate * length of recording
Image file size: image resolution * colour depth
Compression exists to reduce the size of a file.
Compression:
Less bandwidth required
Less storage space required
Shorter transmission time.
Lossless Compression:
A compression algorithm is used such as run-length encoding.
Patters in data are identified and indexed.
No data is permanently lost so can be restored to original format.
(Stores position of word/Number of times word appears.)
Lossy Compression:
Reducing resolution – fewer pixels per unit measurement, less binary to
store.
Reducing bit depth – fewer number of bits to represent each colour, each
pixel has fewer bits.
Data is permanently lost so cannot be restored to original format.
, 2.1 DT, Types and Methods of Data Transmission:
Packets contain:
Header- Sender’s IP address, Destination’s IP address, Packet number.
Payload.
Trailer – Marks end of packet, extra error checks.
Packet Switching:
Data is broken down into equally size fragment known as packets.
Each packet is assigned a packet number before transmission.
Packets take different routes to the destination.
Routers control the routes that the packets take, selecting the fastest
route available.
Packets may arrive out of order.
Once the last packet arrives, packets are reordered using their packet
numbers.
Series- cheap but slow, used in telephone line.
Parallel – fast but skewing and crosstalk, used in RAM and integrated circuits.
Simplex – cheap but slow, used in computer to printer
Half-duplex – cheaper than simplex for bidirectional but slow, used in walkie
talkies.
Full-duplex – fast but expensive, used in broadband connections.
Serial transmission used: Sent over long distances, One bit sent at a time across
one wires so will not skew, Crosstalk will not occur so less chance of errors.
Website uses parallel half duplex: Skewing not problem, not a long distance.
Parallel is the fastest transmission method for large amounts of data.
Advantages of USB: Backward compatible, cannot be inserted incorrectly, high-
speed transmission.
Disadvantages of USB: Maximum cable length is about 5 metres so cannot be
used over long distances, older versions have limited transmissions speeds.
