Computer Science : Fundamentals of Data Representation 3.3

What is the decimal number system?

The decimal number system (base 10) uses 10 different numerals.

0,1,2,3,4,5,6,7,8,9.

What is the binary number system?

The binary number system (base 2) uses 2 different numerals.

0 and 1

What are hexadecimals?

• A number base that uses the numerals 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F.

Has a close link to binary as 4 bits can represent 1 hexadecimal digit.

What are positives on hexadecimals?

More compact than binary so it takes less space on a display and less time to enter. It’s easy for people to understand/remember.

“Hexadecimals takes up less memory space” why is this wrong?

• A computer only stores binary (0s and 1s)

• It’s a human friendly representation used to make long binary readable.

• 1 hexadecimal is 4 bits (1 nibble)

What is bit?

The fundamental unit of information (a 1 or a 0).

What is a byte?

A group of 8 bits.

• Kilo → 1000 bytes (10³ bytes)

• Mega → 1000 kilo (10^6 bytes)

• Giga → 1000 mega (10^9 bytes)

• Tera → 1000 giga (10^12 bytes)

What is a logical binary shift?

Involves moving the bits of a binary number to the left or right

Vacated positions are filled with 0s.

What happens in a logic shift to the left?

Multiplies by 2.

What happens in a logic shift to the right?

Divided by 2.

What is ASCII?

A character encoding system that uses a 7 bit notation that allows for the representation of 128 unique characters.

What is Unicode?

Supports a wider range of characters (emojis, languages, symbols). The first 128 characters are the same as ASCII.

What is a character set?

A collection of characters (letters, numbers, symbols, etc.) that a computer can process and use to represent text. Each character has a unique numerical code.

What is a pixel?

Stands for ‘picture element’. It’s a single point of colour in an image.

What is a bitmap?

Images are broken down into a rectangular grid of pixels. Each pixel will have its own colour value.

What is analogue?

Continuous data - can take any value in a given range.

Between any two analogue values there is another value.

What is digital data?

Has discreet values

There are gaps (jumps). Between digital data values.

How does an ADC (Analogue to Digital Convertor) work?

ADC takes samples of the analogue signal at regular intervals.

The amplitude of each sample is approximated to an integer value.

Each sample is encoded as a binary value.

What is the sampling rate?

A measure of the number of samples taken per second from an analogue signal to create a digital signal.

What is an advantage and disadvantage of analogue data?

Advantage : smoother and captures in higher detail.

Disadvantage : hard to store or reproduce without loss of accuracy.

What is an advantage and disadvantage of digital data?

Advantage : easy to store/copy/process using modern computers.

Disadvantage : higher resolution digital signals need more storage/processing.

What is meant by sampling resolution?

A measure of how many bits are used to represent each sample.

List examples of digital and analogue data:

Digital : software, documents/files.

Analogue : sound waves when you talk, data collected by sensors (output)

What is data compression?

The process of reducing the storage space required for data by encoding the data using fewer bits than the original representation.

What are two examples of data compression?

Lossless : reduces the size of the file without losing any original data. When decompressed, the file is identical to the original.

Lossy : permanently removed some data to reduce file size. Decompressed file is not identical but close enough for most purposes.

What is lossless good for?

• Medical images, legal documents

• When planning to edit or decompress a file many times

• When you want the most detailed image/music.

What is lossy good for?

Smaller file sizes

Sending files quicker

When minor quality loss is acceptable (social media posts)

Examples of lossless formats:

• PNG (images)

• FLAC (audio)

• FFV1 (video)

• PFF (documents)

• SQL (databases)

Examples of lossy formats:

• JPEG (images)

• MP3 (audio)

• MP4 (video)

What is Huffman coding?

Lossless method of data compression

Produces variable length codes where the length of the code depends on the frequency with which a symbol appears in the original data.

What is run length encoding (RLE)?

Lossless method of data compression

Sequence of identical data values are replaces with a single data value and the count of its repetitions.