Topic 3 - Fundamentals of Data Representation

Hexadecimal

Base 16

Denary

Base 10

Binary

Base 2 number system

In Hexadecimal what does A mean in denary?

10

In Hexadecimal what does B mean in denary?

11

In Hexadecimal what does C mean in denary?

12

In Hexadecimal what does D mean in denary?

13

In Hexadecimal what does E mean in denary?

14

In Hexadecimal what does F mean in denary?

15

What is hexadecimal commonly used in computing for? (There are 3 answers)

colour codes, memory addresses, data representation

How many bits does each digit in a hexadecimal number represent?

4 bits (1 nibble)

What do computers use binary for?

to represent all data and instructions

What could a bit pattern represent?

different types of data including text, image, sound and integer

Hexadecimal is preferred over binary or other bases because…?

large numbers can be represented using fewer digits and it is easier to understand than binary, also they are shorter

What is the name given to algorithms that reduce file sizes?

compression

What is the name of the process where compressed data is restored to its original format?

decompression

What are the two types of compression?

Lossy and lossless compression

Lossy compression

permanently loses some data

What can lossy compression result in?

small mistakes known as digital artefacts appearing in images + video

What is an example of a digital artefact?

noise can often be seen where there are contrasting colours

lossless image compression

won't lose any of the original data

how does lossless image compression work?

The algorithm finds groups of repeating data and records the data once along with the number of repetitions.

How does Run Length Encoding work?

uses frequency/data pairs to encode each run length of the same coloured pixel

Give an example of run length encoding to show 4 1's and 12 0's

41 120

Lossless text compression

uses repeated patterns in the original text and encodes each pattern in a dictionary

How does a Huffman tree work?

analyses the frequency with which characters in a body of text are used and then characters are placed in a binary tree structure where the most frequently occurring characters are placed nearest the top of the tree

when is compression used most?

for files and data that are sent via the internet

benefits of using compression are :

download times are reduced, data allowances go further, it's possible to transmit video and music data streams as fast as they are playing

What causes buffering?

if the download speed is slower than the playback speed

What file compression type is JPEG?

lossy

What file compression type is PNG?

lossless

What file compression type is ZIP?

lossless

What file compression type is GIF?

lossless

What file compression type is MP4?

lossy

What file compression type is MP3?

lossy

What file compression type is FLAC/ALAC?

lossless

What file type is JPEG?

photos

What file type is PNG?

images/photos, may include transparency

What file type is ZIP?

document compression

What file type is GIF?

simple images, may include animation

What file type is MP4?

video file format

What file type is MP3?

music format

What file type is FLAC/ALAC?

lossless music format (free/apple)

What two values can a bit be?

0 or 1

What is 8 bits called?

1 byte

What is 2 bits called?

1 crumb

What is 4 bits called?

1 nibble

How many bytes is 1 kB?

1000 bytes

How many kilobytes is 1 MB?

1000 kilobytes

How many megabytes is 1 GB?

1000 megabytes

How many gigabytes is 1 TB?

1000 gigabytes

What does b represent?

a bit

What does B represent?

byte

1+0

1

0+1=

1

1+1

10

1+1+1

11

1+1+1+1

100

What can a binary shift be used to do?

multiply/divide by powers of 2

What does a left binary shift do?

multiplies the number

What does a right binary shift do?

divides the number

If you add binary numbers and the total results in requiring more than 8 bits what occurs?

an overflow error

What is the disadvantage of logical binary shifts?

a loss of accuracy can occur if 1 bit is removed

What do you fill the gaps from a binary shift with?

0s

What type of signal is sound?

analogue

Why must sound be converted to a digital form?

for storage and processing in a computer

How do you digitise sound?

by repeatedly measuring and recording the sound wave

What is an ADC & what does it do?

an analogue to digital converter is used to convert inputs to digital signals

What is DAC and what does it do?

a digital to audio converter is used to convert digital signals to outputs

What does sound sampling mean?

a measurement of amplitude of a sound wave at a given time

The values received from DACs are then stored as a series of ….

binary numbers

What is the sample resolution?

the number of bits used to record each measurement (also known as bit depth) / the number of bits per sample

What does sample resolution determine?

how closely the wave is sampled on the y-axis

The more bits used per sample…

enables the height of the wave to be more accurately measured but increases the file size

What is sampling rate measured in?

Hertz (Hz)

What is sampling rate?

the number of samples taken in a second

How do you calculate sound file sizes?

File size = sampling rate x sample resolution x number of seconds

The greater the sampling rate…

the greater the accuracy, and file size

How does Lossy compression work with MP3?

Removes sounds we can't easily hear or that least affect the perceived playback quality

What is lossy compression useful for?

storing, downloading or streaming

How does lossless compression work?

able to reduce the file size when compressed but don't lose any information

Why are lossy file formats still very popular?

they still reduce the file size well

What is a character set?

A set of letters, symbols and digits that can be represented by a computer

What are the two major character sets in use today?

ASCII and Unicode

What was ASCII originally developed for?

For representing the English alphabet

How many characters does ASCII encode and into what length binary codes?

128 characters into 7-bit binary codes

Where is ASCII commonly used on?

PCs

Why did they create 8-bit ASCII?

So ASCII can be used for many more characters

How many characters can Extended ASCII - 8 bit ASCII encode?

has 256 different characters that can be encoded

How many bits does Unicode use?

16 bits but there is a 32 bit version

Why was Unicode created?

to represent other characters for different languages

How many characters can Unicode encode?

65 536 or >4 billion

TRUE OR FALSE?

Unicode uses different codes to ASCII up to 127?

FALSE : Unicode uses the same codes as ASCII up to 127

What is the term pixel short for?

picture element

What is a pixel?

a single point in an image

What are bitmap images made up of?

pixels

How can a pixel's colour be changed?

By changing the binary value representing the colour of it

How is the size of a bitmap image measured?

In pixels - Width x height

What is image resolution?

The concentration of pixels within a specific area.