Chapter 4: Data Representation Flashcards
Bit
A single binary digit: 1 or 0
Nibble
4 bits
Byte
8 bits
Kilobyte
1024 bytes (2¹⁰ bytes)
Megabyte
1024 kilobytes (2²⁰ bytes)
Gigabyte
1024 megabytes (2³⁰ bytes)
Terabyte
1024 gigabytes (2⁴⁰ bytes)
What is the order of the various kinds of bytes? (Up to terabytes needed)
- Byte
- Kilobyte
- Megabyte
- Gigabyte
- Terabyte
- Petabyte
- Exabyte
Binary
The base 2 number system, which consists of the digits 1 and 0. Used by computers
Why is binary used in computers?
Computers consist of millions of transistors, which are switches that are either on (to store a 1) or off (to store a 0)
Denary
Base 10, which uses the digits 0 through 9. The system we use in everyday life
Hexadecimal
The base 16 number system, which uses the digits 0-9 and the letters A-F. Used to represent groups of four bits at a time
Why is hexadecimal number representation often used?
Hexadecimal is generally easier for people to remember than binary
How would you write the denary number 84 in binary?
1010100
How would you write the denary number 182 in hexadecimal?
B6
How would you write the hexadecimal number FF in denary?
255
How would you write the binary number 11111111 in denary?
255
How would you write the binary number 01011100 in hexadecimal?
5C
How would you write the hexadecimal number 4E in binary?
01001110
How would you store a real number in binary?
Store the main part of the number (the mantissa) and the number of times it needs to be multiplied by 10 (the exponent)
How would you store a date in binary?
Each date would be stored as a unique number within a certain range of dates and time
Character set
The set of symbols that can be represented by a computer, which includes letters, digits, punctuation and control characters
How is each character in a character set represented?
Each character is represented by a numerical code stored as a binary integer
What are some examples of character sets? (3)
- ASCII
- Unicode
- EBCDIC
ASCII
American Standard Code for Information Interchange: a 7-bit character set used by PCs. There is also an extended set that uses 8 bits
What is the ASCII code for the space key?
32
What is the ASCII code for ‘A’?
65
What is the ASCII code for ‘a’?
97
Explain the possible limitations of using the ASCII character set for global communication (4 marks)
- ASCII uses 7 bits to represent each character
- This means that it can only represent 128 (2⁷) different characters
- This is enough to represent the letters and punctuation used in English
- Some languages have much larger alphabets
- Global communication would require a character set that contains all of the alphabets in the world - much more than even the 256 in extended ASCII (8 bits)
Analogue
A continuously changing wave e.g. natural sound
Digital
Data made up of separate values. How data is stored on a computer
How is a sound wave converted from analogue to digital? (2)
- The amplitude (height of the wave) is measured at regular intervals (sampling)
- These values are stored as a series of binary numbers in a file
What do the amplitude and frequency of a sound wave control?
Amplitude: how loud the sound is
Frequency: the sound’s pitch
What is sound quality affected by? (2)
Sample resolution: the more bits used, the better the accuracy of the sound file
Sample interval: the smaller the interval, the better the quality of playback
Sample rate
The number of samples taken per second
Sample interval
The time gap between measurements of the sound wave being taken. A different way of expressing the sample rate
What is the sample rate of:
- A CD?
- A telephone network?
- 41.1 kHz
2. About 8 kHz
Sample resolution OR Bit depth
The number of bits used to store each sample
What is the sample resolution of a CD?
16 bit, which produces a good sound quality
Sound synthesis
When sound stored in a file is recreated by the computer using a DAC and played through speakers
What bit depth and sample rate is becoming more common?
What is the advantage and disadvantage of this?
Bit depth: 24 bit
Sample rate: 96 kHz
Pro: sound quality is better
Con: file sizes are huge
What are two commonly used uncompressed audio file types?
- WAV
2. AIFF
Pros and Cons of WAV and AIFF formats (1 | 2)
Pros
1. High sound quality
Cons
- Large file sizes
- Do not work well for streaming or downloads
Compression
A technique which reduces a file’s size by changing its format
What are the two types of compression?
- Lossy: permanently removes data
2. Lossless: no loss of quality, and can be restored to pre-compression state
MP3
A commonly used, lossy audio compression format
How do MP3s work?
They work by removing frequencies outside the range of human hearing. MP3s can reduce the file size to a twelfth of the original depending on the chosen bitrate
Pros and Cons of MP3s (2 | 1)
Pros
- Ideal for streaming and downloading
- Can be used easily on portable devices e.g. mobile phones
Cons
1. Musicians claim that even the highest bitrate MP3s do not produce the sound quality of a WAV or AIFF
Bitmap image
An image that is stored as a series of values per pixel. Also known as a pixelmap or raster graphics
What are three common image file types?
- JPEG
- GIF
- PNG
Pixel
Short for “picture element”, the smallest component of a bitmap image
Colour depth
The number of bits used to represent the colour of a single pixel in a bitmap image
Higher colour depth provides…
A broader range of distinct colours
What is the colour depth of an image with 4 colours?
2 bits per pixel
What is the colour depth of an image stored as a GIF?
8 bits, allowing a total of 256 different colours
Resolution
The number of pixels in an image expressed as: number of pixels across * number of pixels down
Metadata
Data that serves to provide context or additional information about other data e.g. a file
What is the metadata in the case of image files?
The data the computer needs to interpret the image data in the file e.g. image format, resolution, colour depth and image dimensions
How does a JPEG compress a bitmap file?
It is a lossy compression format that works by discarding details that are generally undetectable by the human eye
What is another way of storing images besides bitmap files?
Vector graphics, which consist of lines with properties such as style, colour, start point and end point. Each of these properties are stored as binary in a file
Data
Facts and figures with no context or format to give them meaning
Information
Data that has been given meaning
ADC
Analogue to Digital Converter: takes real-world analogue information and converts it into a binary representation, which can be stored on a computer
DAC
Digital to Analogue Converter: converts digital data into an analogue signal
In terms of information and data, what do (1) input devices and (2) output devices do?
- Input devices take real-world information and store it as data
- Output devices take data from the computer and present it as information to the user
