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3.1.1: understand that computers use binary to represent data (numbers, text, sound, graphics) and program instructions
Keyword
Definition
binary
system of using a series of zeros and ones to represent data
data
anything that a computer might store or process
graphics
data where binary bits describe colours of shapes or individual pixels
numbers
data where binary bits describe a quantity
sound
data where binary bits describe audio samples over time
text
data where binary bits describe letters and digits
3.1.2: understand how computers represent and manipulate numbers (unsigned integers, signed integers (sign and magnitude, two's complement))
Keyword
Definition
integer
a whole number (e.g. -5)
LSB
the bit on the right that is worth 1.
Magnitude
the size of a number, regardless of whether it is positive or negative
MSB
the bit on the left that is worth the most or indicates the sign of a negative number
Sign
whether a number is positive or negative
Sign and magnitude
a method of representing positive or negative numbers using binary data. Doesn't work for binary addition and has two values for zero.
signed
a number that can be positive or negative
Two's complement
a method of representing positive or negative numbers using binary data. Works for binary addition and only has one value for zero.
unsigned
a number that can only ever be positive
Unsigned integer
a method of representing positive whole numbers using binary data. Start with a bit worth one on the right then double the value of each bit as you move to the left
3.1.3: be able to convert between binary and denary whole numbers (0-255)
Keyword
Definition
Binary
method of describing a data that uses 0s and 1s. Also known as base 2
Bit
a single 0 or 1
Bit value
how much each bit is worth (start with a 1 on the right then double it as you move each bit to the left)
Byte
8 bits used to store a number from 0-255
Denary
method of describing numbers that uses the characters 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9. Also known as base 10
LSB
least significant bit: the bit that's worth 1, at the far right end of a binary value
MSB
most significant bit: the bit that's worth the most, at the far left end of a binary value
3.1.4: understand how to perform binary arithmetic (add, shifts (logical and arithmetic)) and understand the concept of overflow
Keyword
Definition
arithmetic shift
moving binary values one or more bits to the left or right. The sign bit always stays the same.
binary addition
combining two binary values to calculate the sum
binary arithmetic
a mathematical calculation using 0s and 1s
logical shift
moving binary values one or more bits to the left or right, replacing bits on the other end with zeros. The sign bit is ignored.
overflow
when a number is calculated that is too big or too small to be stored with a given number of bits, the extra bits are lost.
3.1.5: understand why hexadecimal notation is used and be able to convert between hexadecimal and binary
Keyword
Definition
binary
method of representing data using 2 characters (0 and 1)
byte
8 bits of binary data that can be represented by two hexadecimal characters
denary
method of representing data using 10 characters (0-9)
hexadecimal
method of representing data using 16 characters (0-9 and A-F)
nibble
4 bits of binary data that can be represented by one hexadecimal character
3.2.1: understand how computers encode characters using ASCII
Keyword
Definition
ASCII
American Standard Code for Information Interchange: the method of using 127 different numbers to each represent a different american english character
Character
an individual letter, digit or punctuation mark
Encode
convert from a character to a number or vice versa
3.2.2: understand how bitmap images are represented in binary (pixels, resolution, colour depth)
Keyword
Definition
bitmap
a way of representing images by storing the colour of each pixel separately
colour depth
the number of bits used to store the colour of each pixel (e.g. 8 bit means 2^8 which is 256 different colours)
pixel
a coloured dot used to make up a tiny part of an image
resolution
the number of pixels used to store an image (width x height)
3.2.3: understand how sound, an analogue signal, is represented in binary
Keyword
Definition
amplitude
how high or low a sound wave is, which can indicate the volume of a sound when it's at its highest or lowest
analogue
a type of signal that is continuous: a never ending amount of detail
digital
a type of signal that is represented as binary bits
digitise
the process of turning an analogue signal into digital samples
resolution
the number of bits used to store each sample.
sample
a measure of the amplitude of a sound at a given point in time
sampling frequency
the number of samples recorded every second. 1KHz is 1000Hz which is 1000 samples every second
sound
an analogue signal caused by vibrations that humans hear as noises, speech and music
3.2.4: understand the limitations of binary representation of data (sampling frequency, resolution) when constrained by the number of available bits
Keyword
Definition
limitation
lack of quality in a digital sound recording
resolution
the number of bits use to store each sample. A lower number means fewer levels of amplitude available to represent the audio recording which means a smaller file size but lower quality.
sampling frequency
the number of samples stored each second. A lower number means fewer samples stored per second which means a smaller file size but lower quality.
3.3.1: understand how to convert between the terms bit, nibble, byte, kilobyte (KB), megabyte (MB), gigabyte (GB), terabyte (TB)
Keyword
Definition
Bit
single 0 or 1
Byte
8 bits
Gigabyte
1024 Mb, or 1024 x 1024 x 1024 bytes
Kilobyte
1024 bytes, or 1024 x 8 bits
Megabyte
1024 Kb, or 1024 x 1024 bytes
Nibble
4 bits
Terabyte
1024 Gb or 1024 x 1024 x 1024 x 1024 bytes
3.3.2: understand the need for data compression and methods of compressing data (lossless, lossy) and that JPEG and MP3 are examples of lossy algorithms
Keyword
Definition
Compression
reducing the number of bits required to store data
JPEG
lossy compression algorithm used to reduce the file size of images so that they're suitable for distribution online
Lossless
a type of compression algorithm which reduces the number of bits required to store data without losing any quality so the original data can be completely recovered
Lossy
a type of compression algorithm which reduces the number of bits required to store data by reducing the quality of the data itself so that it's impossible to recreate the original data
MP3
lossy compression algorithm used to reduce the file size of audio recordings so that they are suitable for distribution online
3.3.3: understand how a lossless, run-length encoding (RLE) algorithm works
Keyword
Definition
Lossless
a type of fully reversible compression algorithm that doesn't lose any quality after encoding or compressing
RLE
run length encoding: where repeated values (e.g. WWWWWWWWBBW) can be encoded by saying the value and how many times it should be repeated (e.g. 8W2B1W)
3.3.4: understand that file storage is measured in bytes and be able to calculate file sizes
Keyword
Definition
Bit
single 0 or 1. Can stored using electrical On/Off signals or magnetic (North / South) polarity
Byte
8 bits
File size
the number of bytes used to store a file
Gb
1024 Mb (1024 x 1024 x 1024 bytes)
Image size
bytes = (width x height x bits per pixel) / 8
Kb
1024 bytes
Mb
1024 Kb (1024 x 1024 bytes)
Sound size
bytes = (sampling frequency (Hz) x resolution (bits) x length (seconds)) / 8
Tb
1024 Gb (1024 x 1024 x 1024 x 1024 bytes)
3.4.1: understand the need for data encryption
Keyword
Definition
Ciphertext
data that can only be read and understood by someone with a password
Decryption
an algorithm that uses a password to convert a ciphertext into a plaintext. Used to receive and process secure data.
Encryption
an algorithm that turns plaintext data into ciphertext data. Used to securely transfer data or prove someone's identity.
Plaintext
data that can be read and understood by anyone without a password
3.4.2: understand how a Caesar cipher algorithm works
Keyword
Definition
13
special Caesar shift that is reversible using the same Caesar shift
26
Special Caesar shift that has no impact (letters are shifted all the way back round the alphabet)
Caesar cipher
an algorithm that shifts each letter a message along the alphabet by a certain number of letters (e.g. A becomes B)
Caesar shift
the number of characters that each letter of a message is moved along the alphabet by in a caesar cipher
Cipher
algorithm used to encode or encrypt data
Decode
algorithm that is used to transform data back to its original form (without a password)
Decrypt
algorithm that uses a password to make secure data readable
Encode
algorithm that is used to transform data from one form to another (without a password)
Encrypt
algorithm that makes data very difficult to understand without a password
3.5.1: understand the characteristics of structured and unstructured data
Keyword
Definition
Structured data
data that has been sorted or organised into groups or linked to related data (e.g. a list of people's phone numbers in alphabetical order by name)
Unstructured data
data that has not been sorted, grouped or linked (e.g. one folder containing hundreds of different types of files with names like "Document 1" and "thing")
3.5.2: understand that data can be decomposed, organised and managed in a structured database (tables, records, fields, relationships, keys)
Keyword
Definition
Database
a way of organising data using tables, records, fields, relationships and keys
Field
one individual category of data that's stored for each record (e.g. "SongName")
Foreign Key
a field that identifies a record in a different table
Key
a field used to identify a record
Primary Key
a field that is unique for every record in a table
Record
a group of related fields that, together, describe one item (e.g. "The National Anthem")
Relational database
a database where tables are linked together using foreign keys
Relationship
a link between tables to show how records are connected to each other
