GCSE - Data representation

What is binary?

A number system with base 2 that only uses the digits 0 and 1.

What is denary?

A number system with base 10 that uses the digits 0–9.

What is hexadecimal?

A number system with base 16 that uses the digits 0–9 and A–F.

What does A represent in hexadecimal?

10

What does F represent in hexadecimal?

15

Why do computers use binary?

Because computer circuits contain transistors which only have two states: ON and OFF.

What are the 8-bit binary place values?

128, 64, 32, 16, 8, 4, 2, 1

Convert 10101010 to denary.

170

Why is hexadecimal used?

To represent binary numbers in a shorter, more readable form.

How many binary bits does one hexadecimal digit represent?

4 bits.

What is 1 + 1 in binary?

10

What is 1 + 1 + 1 in binary?

11

What is overflow?

When there are not enough bits available to store a value.

When can overflow occur?

When the result of a calculation is larger than can be stored in the available bits.

What is sign and magnitude?

A method of storing negative numbers where the leftmost bit indicates the sign.

In sign and magnitude, what does the first bit represent?

0 = positive, 1 = negative

What is two’s complement?

A method used by computers to represent negative binary numbers.

How do you find a two’s complement number?

Write the positive binary number, invert all bits, then add 1.

Why is two’s complement better than sign and magnitude?

It avoids having two representations of zero and makes arithmetic easier.

What happens in a left shift?

All bits move left and zeros are added on the right.

What does a left shift do to a number?

Multiplies it by 2 for each place shifted.

What happens in a right shift?

All bits move right.

What does a right shift do to a number?

Divides it by 2 for each place shifted.

What is ASCII?

A character set that assigns binary codes to characters.

Why is ASCII needed?

Because computers need a way to represent text using binary.

What does ASCII stand for?

American Standard Code for Information Interchange.

What does ASCII store?

Letters, numbers, punctuation and symbols.

Give an example of an ASCII character.

A = 65

What is a pixel?

The smallest individual dot that makes up a digital image.

What is image resolution?

The total number of pixels in an image.

What happens when resolution increases?

Image quality improves and file size increases.

What is colour depth?

The number of bits used to represent the colour of a pixel.

What happens when colour depth increases?

More colours can be displayed and file size increases.

What does a 1-bit colour depth allow?

2 colours.

What does an 8-bit colour depth allow?

256 colours.

What does a 24-bit colour depth allow?

Around 16.7 million colours.

What is the image file size formula?

Resolution × Colour Depth

What is a sample?

A measurement of a sound wave at a particular moment.

What is sample rate?

The number of samples taken each second.

What is sample rate measured in?

Hertz (Hz).

What happens when sample rate increases?

Sound quality improves and file size increases.

What is bit depth?

The number of bits used to store each sample.

What happens when bit depth increases?

Sound quality improves and file size increases.

What is the sound file size formula?

Sample Rate × Bit Depth × Duration

What is compression?

Reducing the size of a file.

What is lossless compression?

Compression where no data is permanently removed.

What is an advantage of lossless compression?

The original file can be perfectly reconstructed.

What is a disadvantage of lossless compression?

Files are larger than with lossy compression.

What is lossy compression?

Compression where some data is permanently removed.

What is an advantage of lossy compression?

Produces much smaller file sizes.

What is a disadvantage of lossy compression?

Some quality is lost permanently.

Give two examples of lossless compression.

PNG and ZIP.

Give two examples of lossy compression.

JPEG and MP3.

Define Binary.

A number system that uses only the digits 0 and 1.

Define Hexadecimal.

A base-16 number system that uses the digits 0–9 and A–F.

Define Overflow.

When there are insufficient bits available to store a value.

Define ASCII.

A character set that assigns binary values to characters.

Define Pixel.

The smallest element of a digital image.

Define Resolution.

The number of pixels in an image.

Define Colour Depth.

The number of bits used to represent the colour of a pixel.

Define Sample Rate.

The number of sound samples taken per second.

Define Bit Depth.

The number of bits used to store each sound sample.

Define Lossless Compression.

Compression where no data is permanently removed and the original file can be perfectly reconstructed.

Define Lossy Compression.

Compression where some data is permanently removed, reducing file size but also reducing quality.