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4a: Recall that representations are used to store, communicate, and process information.
Keyword
Definition
communicate
sharing a message with someone else who might not have heard it before
data
unprocessed information (meaningless letters, numbers or symbols)
information
processed data (letters, numbers or symbols that have been organised and put into context)
process
understanding a message so that you can respond appropriately
representation
a way of describing a message so that it can be stored, communicated or processed
store
keeping a message safe so that it can be remembered for later
4b: List examples of representations.
Keyword
Definition
alphabet
a way of representing messages using written symbols to represent words and sounds
ASCII
a way of representing messages using a different number for each letter of the alphabet and used by computers to send the numbers as binary digits
braille
a way of representing messages using bumps on a surface that blind people can read using their fingers
hieroglyphics
a way of representing messages using pictures to represent words
morse code
a way of representing messages using sequences of dots and dashes often transmitted as beeps over radio waves
semaphore
a way of representing messages using sequences of flags to send signals by line of sight
4c: Provide examples of how different representations are appropriate for different tasks.
Keyword
Definition
alphabet
representation that is ideal for making notes in your school exercise books
ASCII
representation that is ideal for sending emails across the Internet
braille
representation that is ideal for enabling blind people to read by running their fingers over bumps
morse code
representation that is ideal for sending coded messages over radio waves across the ocean
semaphore
representation that is ideal for lifeguards on a beach to send a message via line of sight when it's too far to shout
4d: Recall that characters can be represented as sequences of other symbols.
Keyword
Definition
character
a letter, numerical digit or punctuation mark
representation
a way of storing data so that it can be understood and shared
sequence
more than one character appearing in order
symbol
a way of representing something
4e: Measure the size of a representation as the number of symbols that it contains.
Keyword
Definition
base
the number of different symbols available to use in each place in a sequence
base 10
a representation that has 10 different symbols (e.g. writing numbers in decimal with the numbers 0 - 9)
base 16
a representation that has 16 different symbols (e.g. describing colours in hexadecimal with 0-9 and A-F)
base 2
a representation that has two different symbols (e.g. binary with 0 and 1)
base 26
a representation that has 26 different symbols (e.g. writing messages using the letters A-Z)
base 64
a representation that has 64 different symbols (e.g. describing the contents of files using A-Z, a-z, 0-9 and some additional punctuation symbols)
message length
the number of symbols needed in a sequence to represent a message
4f: Provide examples of how symbols are carried on physical media.
Keyword
Definition
CD
stores binary data on spinning discs covered in pits and lands which either absorb or reflect laser light
DVDs
stores binary data on spinning discs covered in pits and lands packed closely together which either absorb or reflect laser light
Ethernet
transmits binary data by sending and receiving electrical pulses down pairs of wires between two computers
Fibre Optic
transmits binary data by sending and receiving pulses of light inside a cable that reflects the signal so it can be detected at the other end
Hard Disk
stores binary data on spinning discs covered in tiny sectors which can be magnetised in one of two directions
Solid State Drive
stores binary data without any moving parts using electronic chips containing NAND gates and flash memory
WiFi
transmits binary data by sending and receiving radio pulses switched on and off at a very high frequency
4g: Explain what binary digits (bits) are, in terms of familiar symbols, e.g. digits or letters.
Keyword
Definition
bit
one binary digit (either 0 or 1)
byte
a sequence of eight bits (from 00000000 to 11111111)
digit
a single character, letter or numerical symbol
nibble
a sequence of four bits (from 0000 to 1111)
4h: Measure the size of a bit sequence as the number of binary digits that it contains.
Keyword
Definition
bit
an individual binary digit (0 or 1)
byte
a sequence of eight binary digits
gigabyte
a sequence of 1,000,000,000 bytes
kilobyte
a sequence of 1,000 bytes
megabyte
a sequence of 1,000,000 bytes
nibble
a sequence of four binary digits
4i: Describe how natural numbers are represented as sequences of binary digits.
Keyword
Definition
bit
a single binary digit (0 or 1)
bit value
how much an individual bit is worth within a sequence of binary digits
byte
a sequence of 8 bits which can represent a value between 0 and 255
least significant bit
the bit with the lowest value (1) which can be found on the right, at the end of a sequence of bits
most significant bit
the bit with the highest value which can be found on the left, at the start of a sequence of bits
natural number
a whole number (without a decimal place)
nibble
a sequence of four bits which can represent a value between 0 and 15
4j: Convert a decimal number to binary and vice versa.
Keyword
Definition
binary
a base 2 number system (using digits 0 and 1) where each digit is worth 2 times as much as the digit to its right
decimal
a base 10 number system (using digits 0-9) where each digit is worth 10 times as much as the digit to its right
denary
another name for decimal
unsigned
a number that can only greater than or equal to zero
4k: Convert between different units of representation size.
Keyword
Definition
bit
1 individual binary digit (1 or 0)
byte
8 bits
gibibyte
1,024 mebibytes
gigabyte
1,000 megabytes
kibibyte
1,024 bytes
kilobyte
1,000 bytes
mebibyte
1,024 kibibytes
megabyte
1,000 kilobytes
nibble
4 bits
tebibyte
1,024 gibibytes
terabyte
1,000 megabytes
4l: Provide examples of how binary digits are physically represented in digital devices.
Keyword
Definition
bit
an individual binary digit
laser
light and sound emitting radiation (a focussed beam of light)
magnetic surface
covering of a spinning platter inside a hard disk drive which represents 1s and 0s by flipping the polarity of tiny magnetic areas
NAND gate
logic gate used in solid state storage devices to represent 1s and 0s
pits and lands
bumps on a CD, DVD or BLU-RAY disc which absorb or reflect laser light so it can be detected by a sensor as 1s and 0s
polarity
the direction of a magnetic or electric field
sensor
a device that can detect something and turn it into an electrical signal
transistor
digital switches used to process electrical signals which represent 1s and 0s
4m: Recall that binary digits represent all information that is stored, transmitted, and processed by computers.
Keyword
Definition
ASCII
American Standard Code for Information Interchange (a way of converting each letter of the latin alphabet into a number so it can be represented in binary)
bitmap image
can be represented by binary digits by describing the colour of each using numbers and then converting each number into binary
numbers
can be represented in binary by converting from decimal to binary
sound
can be represented by binary digits by regularly sampling the amplitude (size) of a sound wave and converting each sample into binary
text
can be represented by binary digits by giving each letter a numerical value then converting that into binary
vector image
can be represented by binary digits by describing each shape and colour using numbers and then converting each number into binary
video
can be represented by binary digits by splitting it into frames of still images and describing each frame as a sequence of coloured pixels and sound
4n: Describe how characters are represented as sequences of binary digits.
Keyword
Definition
ASCII
American Standard Code for Information Interchange (a way of using 7 bits to describe each letter in the Western European or American alphabet)
unicode
Standard that uses more than 7 bits to describe each letter in the alphabet so that special characters can be represented that can't be described using ASCII (like £ or letters with accents)
