Autumn mocks revision

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Revision for Autumn Mocks

• Binary conversion

• Hexadecimal conversion

• Binary Addition

• Binary Shifts

• Character sets

• Units of information

• Sound

• Images

• Compression (lossy and lossless)

​Hexadecimal numbers are a base-16 system as there are 16 digits.
The first ten digits are 0 to 9, and the remaining 6 digits are represented by the letters A, B, C, D, E and F. It is used in computing as each 8-bit binary number needs only two hexadecimal digits, and is much easier to write.

Hex is useful because large numbers can be represented using fewer digits. For example, colour values and MAC addresses are often represented in hex.

Additionally, hex is easier to understand than binary. Programmers often use hex to represent binary values as they are simpler to write and check than when using binary.

Why use Hex?

A byte of data like 10110111 can be written as B7 in hexadecimal.

​01011100

​0101 1100

1100

​0101 1100

​0101

1100

​0101 1100

​0101

​8 4 2 1

​8 4 2 1

1100

​0101 1100

​0101

​8 4 2 1

​8 4 2 1

​5

​12

1100

​0101 1100

​0101

​8 4 2 1

​8 4 2 1

​5

​12

​5

C

​Calculating file size

​Size of sample =

(number of samples per second) x (number of bits per sample) x (length of sample in seconds)

sample rate x bit depth x time​

​Calculating file size

​Size of sample =

(number of samples per second) x (number of bits per sample) x (length of sample in seconds)

sample rate x bit depth x time​

​Calculating file size

​Size of sample =

(number of samples per second) x (number of bits per sample) x (length of sample in seconds)

sample rate x bit depth x time​

​Calculate the file size in bits for a 0.5 minute sound recording that has used a sample rate of 500 Hertz (Hz) and a sample resolution of 4 bits.  

Pixel

Picture Element

A single point (of colour) in an image

​0 = White
1 = Black

​image file size=
resolution x bit depth

​

image file size = colour depth x image height (px) x image

width (px)

​File size

The image on the right-hand side was
originally 1.53 megabytes.

Lossy compression: image example

When this bitmap image file
is compressed, the size reduced from 1.53
megabytes to 252 kilobytes.
Achieving a reduction in file size
of around 90%.

This is a huge difference in file size,
yet the pictures look very similar to
the human eye.

Lossy compression: image example

Lossy compression:
image example

Another example of lossy compression is
MP3.

When sound is recorded, it will include
samples of sounds that the human ear
cannot hear. (very high-pitched sounds
or very low-pitched sounds)

When a WAV file is compressed to
create an MP3 file, the compressed file
is typically 90% smaller than the original.

Think of how long podcasts / audiobooks can be and the amount of sound that is recorded but unneeded / unheard

Lossy compression: sound example

Multiple Choice

Calculate the binary addition:
01
11
Use binary addition rules + whiteboards!

• 101
• 11
• 111
• 100

Multiple Choice

Calculate the binary addition:
01111
11011
Use binary addition rules + whiteboards!

• 101010
• 11101001
• 11001011
• 1010101111

Multiple Choice

Calculate the binary addition:
Use binary addition rules + whiteboards!

• 10100100
• 10010100
• 11000100
• 01011110

Multiple Choice

Convert 128 into 8 bit Binary

• 1000 0000

• 0100 0000

• 1111 1111

• 1280 0000

Multiple Choice

Convert 20 into 8 bit Binary

• 0001 0100

• 10100

• 0010 0100

• 0000 0010

Reorder

Reorder the following from smallest to largest

• bit

• Byte

• Kilobyte

• Megabyte

• Gigabyte

1

2

3

4

5

• 1
• 2
• 3
• 4
• 5

Dropdown

To get from Terabytes to megabytes you ​

Select answer

by 1000 then​

Select answer

​ by 1000

Multiple Choice

What is the possible effect of a binary right-shift operation?

• Loss of precision

• Increased precision

• Loss of bits

• Increased number of bits

Multiple Choice

How many bits are used in (standard) ASCII? (1-4

• 16
• 1
• 7
• 8

Multiple Choice

What is a benefit of extended ASCII?

• All major languages can be represented

• Many European languages can be represented as accents are included

• Nothing as it just uses more space to store each letter

Multiple Choice

The more often you record a sample the ___________ the playback will sound

• Lower

• Worse

• Louder

• Smoother

Multiple Choice

The number of samples taken per second is called

• sample rate

• frequency rate

• analogue rate

• digital conversion rate

Multiple Choice

The amount of bits allocated per sample is called the

• bit rate

• sample rate

• bit depth

• bit sample

Multiple Choice

The bit rate is calculated using..

• Sampling Frequency x Sample Size

• Whole sample size x sample depth

• sample height x width

Multiple Choice

The calculation to get the file size is...

• sample rate(bits) x bit depth(Hz) x time(s)

• sample rate(Hz) x bit depth(bits) x time(hours)

• sample rate(s) x bit depth(Hz) x time(s)

• sample rate(Hz) x bit depth(bits) x time(s)

Multiple Choice

A pixel is...

• a type of computer software for image editing.
• a color filter used in photography.
• the smallest unit of a digital image or display.
• the largest unit of a digital image or display.

Multiple Choice

Colour depth is...

• the resolution of a digital image
• the size of the image file in bytes
• the total number of colors in an image
• the number of bits used to represent the color of a single pixel in a digital image

Multiple Choice

If an image has only the colours black and white how many bits are needed to store the colours?

• 2 bits
• 1 bit
• 8 bits
• 4 bits

Multiple Choice

If 4 bits are used how many colours can be stored in an image?

• 16
• 32
• 4
• 8

Multiple Choice

The formula to work out image resolution is...

• Width + Height in pixels
• Width - Height in pixels
• Width x Height in inches
• Width x Height in pixels

Multiple Choice

Metadata is...

• Data about images.
• Data about users.
• Data about files.
• Data about data.