Memory And Storage (part 2) Flashcards
How many bits are in a byte?
8
How many bytes are in a kilobyte?
1000
How would you calculate the file size of a text file?
Number of bits per character x number of characters
How would you calculate the file size of an audio file?
Sample rate x duration (s) x bit depth
How would you calculate the file size of an image?
Colour depth x image width (px) x image height (px)
What do binary shifts do?
Divide or multiply the number
What are the problems with binary shifts?
- Can create an overflow
- Number is rounded and therefore loses precision
What is metadata?
Additional information stored about an image eg. height, width
What is a character set?
A defined list of characters recognised by the computer
Give 2 examples of character sets
- ASCII
- UNICODE
What is ASCII?
Early 7 bit character set which was later extended to 8 bits
What is UNICODE?
The modern most commonly used character set that uses 24 bits
How many characters can be used in a 7 bit character set?
27 = 128
How are images represented on a computer?
As a series of pixels which is represented in binary, each pixel has a specific colour and each colour has a specific code
What effect does increasing the colour depth have on an image?
- Increased file size
- Increased quality
What effect does increasing the resolution have on the image?
- Increased file size
- Increased image quality
What is colour depth?
The number of bits for each pixel
What factors affect the quality of digitally converted sound?
- Sample rate
- Bit depth
What is sample rate?
How often you record the amplitude of the sound wave
How is sound converted into a file?
The sound is sampled by measuring the height of the wave at set intervals and then converted into binary
What is sample rate measured in?
Hertz (Hz)
What effect does increasing the sample rate have on the file?
- Higher quality sound
- Larger file size
What is the bit depth?
The number of bits used for each sample
What does compression do?
Reduce the size of a file so it takes up less space on a storage device
Why would you need compression?
- To free up storage, allowing more data to be stored
- Quicker download and transfer speeds (allowing streaming)
What are the 2 different compression types?
- Lossy
- Lossless
What is lossy compression?
Compression of files when the colour depth and/or resolution is reduced
What are the advantages of lossy compression?
- Significantly reduces file size
- Hard to notice change in image quality
Name a disadvantage of lossy compression?
Lower image quality as there is less detail
What is lossless compression?
Compression when the way the image is encoded is changed but the image itself stays the same
What are the advantages of lossless compression?
- No detail is lost
- Reduces file size without losing any data
Name a disadvantage of lossless compression?
- Only works with images that have a lot of repeating colour eg. cartoons
- Doesn’t reduce file size as much as lossy compression
