Technical Implecations Flashcards
What is a full backup?
Copy every item of data, creating a complete second version of what is stored.
What is a differential backup?
Does not take as long as a full backup as only the data that has changed since the last full backup is stored. They require less storage space.
What is an incremental backup?
More efficient as it will only save changes since the last backup of any kind, regardless of whether the last backup was a full, differential or incremental backup.
What are the two types of compression?
Lossless and lossy.
What is lossless compression?
Results in none of the detail being lost in the compression file.
What is lossy compression?
- Results in some of the details being lost in the compressed file.
- Once the file is compressed the original data file can never be recreated (uncompressed)
- The data removed by lossy compression is lost forever
What happens in lossless compression?
- lossless techniques encode the data in a way that the file may be uncompressed, recreating the original file
- non of the original data is lost
- uses maths algorithms to reduce amount of information stored
- takes advantages of repeating patterns
- used by GIF but this can only use 256 colours
- used by PNG the successor to GIF. Allows 24 bit ‘true colour’
- also used for sound compression, Dolby, MP4, WMA
What happens during lossy compression?
- losses some data to reduce file size
- either by math algorithms
- it looses data our eyes and brain will not miss
- able to save more space than lossless
- only suitable if data lost does not make file useless
- works by removing details such as area in a blue sky
- jpeg supports 16 million colours
- greater compression ratio than lossless
- not a good compression type if you want to do either edits or compressions
What are lossless compression methods?
- Free lossless audio code
- Run length encoding (graphic)
How does lossy compression work with audio?
- removing sounds that are inaudible to the human ear
- when two similar sounds occur at the same time, the quieter sound is removed
- quiet sounds stored as mono not stereo
- can compress file to 1/12 of original size
What is Discrete Cosine Transformation ( DCT)?
- encoding (graphic)
- applies a mathematical algorithm
- based on a cosine wave to groups of 64 (8x8) pixels
What are the two types of video compression?
- Interframe: stores only the information that has changed between each frame of a video
- Intraframe: treated each frame of the video as a separate bit mapped graphic
What is beta testing?
Pre release testing. A sample group of the target audience tries the product out. Tests versions of commercial software are now commonly distributed to a wide audience on the web.
