Fundamentals of Data Representation

Flashcards made from the AQA GCSE Computer Science (8525) specification - section 3.3 (Fundamentals of data representation) Skills: ★ Number bases inc. bit shifts ★ RLE (Run Length Encoding) ★ Huffman encoding

What base is decimal?

Decimal is base 10

What base is binary?

Binary is base 2

What base is hexadecimal?

Hexadecimal is base 16

How do we represent number 10-15 in hexadecimal?

We represent number 10-15 in hexadecimal using letters

What does a bit shift to the left/right do?

★ Bit shift to the left: multiplies number by 2 ★ Bit shift to the right: divides number by 2

What are the advantages of hexadecimal over binary?

★ Simpler to remember large HEX numbers than binary numbers ★ HEX numbers are shorter ➜ Fewer input errors than binary numbers

What is a bit?

A bit is the fundamental unit of information

How do we represent a bit?

We represent a bit with 'b'

What's a byte?

A byte is a group of 8 bits

How do we represent a byte?

We represent a byte using 'B'

How much is a nibble?

A nibble is 4 bits (1/2 a byte)

What's a kilobyte?

A Kilobyte is 1000 bytes

What's a megabyte?

A megabyte is 1000 kilobytes

What's a gigabyte?

A gigabyte is 1000 megabytes

What's a terabyte?

A terabyte is 1000 gigabytes

What can be stored by a byte?

A single ASCII character can be stored by a byte

Wha can be stored by a kilobyte/megabyte?

★ Songs ★ Pictures ★ Documents can all be stored with KB

What can be stored by a gigabyte?

★ High definition videos ★ Complex applications can be stored by gigabytes

How do we abbreviate units of information (e.g. bytes)?

★ We abbreviates units of information using the first letter of the prefix +B ★ E.g. KiloByte —> kB

What is an advantage of ASCII?

An advantage of ASCII is it has all standard American letters in just 7 bits

What is a disadvantage of ASCII?

A disadvantage of ASCII is can't display different alphabets and special characters

What are the first 127 Unicode characters?

The first 127 Unicode characters are the corresponding ASCII characters

What is an advantage of Unicode over ASCII?

An advantage of Unicode over ASCII is it can represent different alphabets and special characters

What is a disadvantage of Unicode?

Unicode uses more storage space per character than ASCII

Given 'A' in ASCII is 65, what is 'D'

Given 'A' in ASCII is 65, D is 68

What is a character set?

Character sets are collections of characters that a computer recognises from their binary representation.

What are alphanumeric characters?

Alphanumeric characters include: ★ Uppercase and lowercase characters ★ Numbers/digits ★ Symbols

What are special commands?

Special commands are commands that do certain commands e.g.: ★ Space ★ Enter ★ Delete

What do character sets contain?

Character sets contain: ★ Alphanumeric characters ★ Special commands e.g. space

What is a pixel?

★ A pixel is short for picture element ★ A dot on the screen (smallest indivisible unit for pictures)

What does bitmap mean?

A bitmap is a grid of pixels (map of bits)

What is resolution in computing? [Images]

The resolution is the width and height of the image

What's colour depth?

Colour depth is the amount of bits of colour allowed for each pixel on the image

What's image size?

Image size is the amount of pixels an image contains

What is the formula for image size?

The formula for image size is: Size = width x height x colour depth

How is white and black displayed in images?

0 - is displayed as black on images 1 - is displayed as white on images

What is the formula for number of colours available given the colour depth?

Number of colour = 2ᵇ b = number of bits

What is metadata?

Metadata is a set of data that describes and gives information about other data.

What is analogue data?

Analogue data is continuous and there are no limits to the values that the data can take.

What is digital data?

Data that changes discreetly through a finite set of possible values

Is sound an analogue or digital piece of data?

Sound, which is made up of sound waves, are an analogue piece of data

How does a computer interpret sound despite it being analogue?

To understand sound, a computer makes the analogue data digital data by taking measurements at specific intervals

What is sampling rate?

Sampling rate is how often the data is being measured

What unit is sampling rate measured in?

Sampling rate is measured in Hz (s⁻¹)

What is bit rate?

Bit rate is the number of bits used per second of audio

What is the formula for bitrate?

Bitrate = recs x res

How is sound recorded?

Sound is recorded by converting sound waves into electronic signals that can be processed and stored. Sound is reproduced by converting electronic signals back into sound waves.

What is sampling resolution?

Sampling resolution is the number of bits per sample

What is the advantage of a higher sampling resolution?

A higher sampling resolution is that it will pick up on quieter sounds in the presence of louder sounds

What is the formula for calculating file size for sound?

The formula for calculating file size for sound is: File size (bits) = rate x res x secs ★ Rate - Sampling rate (Hz) ★ Res - Sampling resolution (bits) ★ Secs - seconds (s)

What are 2 advantages of compression?

The advantages of compression include: ★ Less file size ★ Faster download speeds ✔︎ This is because it takes up less bandwidth

What is lossy compression?

Lossy compression is compression where some of the information is permanently eliminated

When would we use lossy compression?

We would use lossy compression when losing some data only means a drop in quality e.g. images,sound

What are 3 examples of lossy compression?

Two examples of lossy compression are: ★ JPEG (for images) ★ MP3/AAC (for sound)

What are 3 advantages to lossy compression?

Advantages of lossy compression include: ★ File takes up a lot less space (also compared to lossless) ➜ Files can be transmitted quicker ✔︎ Takes up less bandwidth ★ Commonly used (lots of software can read it)

What are 3 disadvantages to lossy compression?

Disadvantages to lossy compression include: ★ Worse quality and resolution ★ Can't be used on text or software files where all info is important ★ Cannot restore to original state (loses data)

What is lossless compression?

Lossless compression is compression where all the original data can be recovered when the file is decompressed

When is lossless compression used?

Lossless compressions is typically used when all the data is important (e.g. text files, code)

What are 4 examples of lossless compression?

Examples of lossless compression include: ★ Text files ★ PNGs (images) ★ ZIP (files and folders) ★ FLAC (audio)

What are 3 advantages to lossless compression?

Advantages of lossless compression include: ★ Data is only removed temporarily so there is no reduction in quality, the compressed file should look or sound like the original ★ Lossless files can be decompressed ★ Lossless compression can be used on text and software files

What are 2 disadvantages to lossless compression?

★ File takes up a lot more space ➜ Files cannot be transmitted as quickly ✔︎ Takes up more bandwidth

How do run length encoding (RLE) work?

★ Run length encoding (RLE) works by grouping data by the frequency and the character

When is RLE useful?

Run length encoding (RLE) is useful when lots of pieces of data are repeated e.g. pppprrrr9999

What are two GCSE examples of lossless compression algorithms?

Two examples of lossless compression algorithms include: ★ Huffman encoding ★ Run length encoding (RLE)

How do you interpret Huffman trees?

To interpret Huffman trees, go down the branches and read the 1s and 0s until you reach the character