Computer Science - Fundamentals of data representation

Theory

What is the capacity of a device

How much data can be stored in the given storage medium.

What is the smallest unit of data called

A bit or binary digit.

4 bits is called

Nibble

8 bits is called

A byte.

1000 bytes is called

A kilobyte (KB).

1000KB is called

A megabyte (MB).

1000MB is called

A gigabyte (GB).

1000GB is called

A terabyte (TB).

How to calculate required capacity

R = no of files*size of a single file

Why do computers use hexadecimal instead of binary

• It’s easier for humans to read and understand.

• Large number can be represented using fewer digits.

• Allows us to find errors more easily.

In what programming languages is hex used in

Machine code and assembly language

What is hex used for

• Programming languages.

• Can represent numbers stored in main memory.

• Can be used in the debugging state of programming.

How many hex digits represent 8 bits (a byte)

Two hex digits represent 8 bits.

What is a MAC address

A number that uniquely identifies a networked device

What is the max denary number represented using hex digits

255

0+0=

1+0=

1+1=

1+1+1=

0

1

0 carry 1

1 carry 1

What is a binary shift

A technique for performing multiplication or division on a binary number.

What happens in a left binary shift

Each digit is moved 1 place to the left or multiplied by 2

What happens in a right binary shift

Each digit is moved 1 place to the right or divided by 2

What are the 2 character sets computer uses

1. American Standard Code for Information Interchange (ASCII)

2. Unicode

What is the most common form of Unicode

UTF-8 uses between 8 and 32 bits to represent every character

How many bits is ASCII represented by

7 bits (max of 128 characters)

Why is Unicode better than ASCII

Because Unicode covers all languages, ASCII covers only English

How are digital images stored as

Bitmaps

What is colour depth

The amount of bits used to store each colour

What is resolution

It represents the number of pixels in an image.

Formula for finding no of pixels in an image

Width*Height

What is metadata

Extra information added to an image file

Examples of metadata

Resolution, colour depth, time and date of the photo taking, encoding format

Formula for calculating file size in bits

Image width*image height*colour depth (in bits)

Formula for calculating file size in bytes

File size in bits/8

In a black and white image how are the pixels represented

0 represents black

1 represents white

What is sample size

The number of bits used to store each sample

What is sampling rate

The number of samples taken per second

How is the quality of an audio increased

By increasing the sample size and the sampling rate

What is bit rate

The amount of data stored per second of an audio

How is bit rate calculated

Sample rate * sample size

How does increasing audio increase file size

Because the sampling rate and sample size is increased

What is compression

Reduction of file size

What are the 2 types of compression

Lossless and Lossy

Features of lossless compression

• None of the original data is lost.

• An algorithm can be used to perfectly restore the original file when needed.

• This is especially useful for executable files, where all of the data is necessary.

• Lossless compression causes file size to reduce moderately.

Features of lossy compression

• An algorithm is applied to remove unnecessary detail from the original file.

• Some data is permanently lost, but enough remains so that the file is still useful and there is barely a noticeable difference.

• Lossy compression results in dramatic file size reduction.

What is run length encoding (RLE)

A type of lossless compression that replaces repeating sequences of binary digits with more efficient representations.

What is Huffman coding

A type of lossless compression for text compression which reduces file size by assigning a fewer no of bits to the most frequently used characters