Section 7: Data Representation Flashcards
What is a logic gate and what does it do?
Logic gates are special circuits built into computer chips. They receive binary data, apply a Boolean operation, then output a binary result.
From smallest to largest, State the name and size of each unit used by a computer.
Bit (b) - A single binary digit (0 or 1) Nibble - 4 bits Byte (B) - 8 bits Kilobyte (kB) - 1000 bytes Megabyte (MB) - 1000 Kilobytes Gigabyte (GB) - 1000 Megabytes Terabyte (TB) - 1000 Gigabytes Petabyte (PB) - 1000 Terabytes
State 3 advantages of the use of hexadecimal.
1) It’s simpler to remember large numbers in hex - they’re far shorter than binary numbers.
2) Due to hex numbers being shorter, there’s less chance of input errors.
3) It’s easier to convert between binary and hex than binary and denary
What is a character set?
Character sets are collections of characters that a computer recognises from their binary representation.
Name the three mainly used character sets.
ASCII, Extended ASCII and Unicode.
How many characters can ASCII represent and why?
ASCII uses a 7 bit binary code to represent its characters, meaning it can represent 128 characters, including all letters in the English alphabet, numbers, symbols and commands.
How many characters can Extended ASCII represent and why?
Extended ASCII uses a 8 bit binary code to represent its characters, meaning it can represent 256 characters, including all that ASCII can represent, it’s useful for European languages like French and German which include accents on some of the vowels.
Why is Unicode often the best character set?
Unicode uses 16 bit or 32 bit binary codes so it can cover all major languages, even those that use a completely different alphabet like Greek, Russian and Chinese
Whats the other name for an image?
Bitmap Image, made up of pixels.
Describe bitmap images. (In terms of colour depth)
The colour of each pixel is represented by a binary code. The number of colours available in an image is related to the number of bits the code has. You can make a greater range of shades and colours by increasing the number of bits for each pixel.
What is colour depth?
The number of bits used for each pixel.
What is resolution? (Images)
The resolution is the density of pixels in an image - usually measure in dots per inch (dpi)
What happens when you increase colour depth or resolution and why?
This results in more bits being in the image. This improves image quality, but also increases the file size.
What is Metadata? And give some examples.
Metadata is the information stored in an image file which helps the computer recreate the image on screen from the binary data in each pixel.
Metadata usually includes the image’s file format, height, width, colour depth and resolution.
Without metadata, devices would not be able to display the image on screen as intended.
Explain how sound is recorded and stored on a computer.
Sound is recorded by a microphone as an analogue signal. (A piece of continually changing data)
This analogue signal is then converter to digital data so that computers can read and store sound files, this process is called sampling.
Explain how sampling works.
You sample the amplitude of the sound wave at regular intervals, and creates a curve digitally (looking like bar chart with varying heights (amplitude) for each interval)
What are sampling intervals?
Sampling intervals are the gaps between each of the points where the analogue recording is sampled. E.g. the audio file might be sampled every 5 milliseconds - the sampling interval would be 5 milliseconds.
What is sampling frequency?
Also known as sample rate, is how many samples you take in a second - it’s usually measured in kilohertz (kHz)
What is sample size?
Sample size is the number of bits available for each sample (like colour depth but for sound samples)
What is bit rate?
Bit rate is the number of bits used per second of audio - found using :
Bit rate = Sampling frequency x Sample size
What happens when you increase sampling frequency and sample size?
Increasing the sampling frequency means the analogue recording is sampled more often. The sampled sound will be better quality and more closely match the original recording.
Increasing the sample size means the digital file picks up quieter sounds, even if they’re happening at the same time as louder ones. This also results in a sampled sounds that is closer to the quality of the original recording.
Increasing these two, increases the bit rate, this will increase the number of bits in a sound file, which means a larger file size.
What are the uses of compression?
1) Smaller files take up less storage space on a device.
2) Streaming and downloading files from the internet is quicker as they take up less bandwidth.
3) It allows web pages to load more quickly in web browsers
4) Email services normally have restrictions on the size of the attachment you can send - compressing the file allows you to send the same content with a much smaller file size.
How does lossy compression work?
Lossy compression works by permanently removing data from the file - this limits the number of bits the file needs and so reduces its size.
How does lossless compression work?
Lossless compression makes the file smaller by temporarily removing data to store the file and then restores it to its original state when its opened.
What are the Pros & Cons of LOSSY compression?
PROS:
1) Greatly reduced file size, meaning more files can be stored.
2) Lossy files take up less bandwidth so can be downloaded and streamed more quickly
3) Commonly used therefore lots of software can read lossy files.
CONS:
1) Lossy compression loses data - the file can’t be turned back into the original.
2) Lossy compression can’t be used on text or software files as these files need to retain all the information of the original.
3) Lossy files are worse quality then the original. But, this loss in quality is normally unnoticeable.
What are the Pros & Cons of LOSSLESS compression?
PROS:
1) Data is only removed temporarily so there is no reduction in quality - the compressed file should look or sound like the original.
2) Lossless files can be decompressed - turned back into the original.
3) Lossless compression can be used on text and software files.
CONS:
1) Only a slight reduction in file size, so lossless files still take up quite a bit of storage.
Give some examples of Lossy file types.
MP3 (audio) AAC (audio) JPEG (image)
Give some examples of Lossless file types.
FLAC (audio) TIFF (image) PNG (image)
