Data Representation Flashcards
What are the three types of files?
Text
Sound
Image
How do you calculate text file size?
Bits per character x number of characters
How do you calculate the size of sound files?
Sample rate x duration(s) x bit depth
How do you calculate the file size for image files?
Colour depth x image height(px) x image width
What is an overflow error?
An overflow show that the result of the calculation is too big for it to be stored in 8 bits
What are the rules of binary addition?
0 + 0 = 0
0 + 1 = 1
1 + 1 = 0 carry 1
1 + 1 + 1 = 1 carry 1
What does the result of one left shift leave?
The original number is multiplied by 2
What does one right shift produce?
The original number is divided by 2
What is a character set?
A defined list of characters recognised by the computers hardware and software. Each character is represented by a single number.
What are examples of character sets?
ASCII - American standard code for information interchange- 128 character
Extended ASCII- 256 characters
Unicode- 16 million character
What is metadata?
Metadata is additional data stored with the images to define the width, height, colour depth and colour palette
What are the two types of compression?
Lossy
Lossless
What are some effects of lossy compression?
Some of the data is lost and can’t be recovered
Greatly reduces the file size
Reduces the quality of the image/ sound
Suitable for images, sound and video
Cannot be used on text and executable files
What are some effects of lossless compression?
None of the data is lost, it is just encoded differently
Can be turned back into original format
Can be used on all types of data
Usually less effective than lossy compression at reducing the files size
Most suitable for documents and executable files
Need for primary storage
Main memory is required to temporarily store the programs, instructions and data the computer needs whilst in operation.
Ram properties
Volatile- all data lost
Can be written to, and read from
Used for the computers working memory for instructions, programs and data
Rom properties
Non volatile- data permanently retained without power
Used for the computer start up instructions and in embedded systems.
Read on,y so cannot be written to
Define virtual memory
Virtual memory is used when there simply isn’t enough space in RAM for all programs and data you are currently working on
Why secondary storage
Need secondary storage for longer term storage of files and data because it is non volatile
What is a bitmap?
Made up of picture elements or pixels
Advantages of lossy
Smallest file size, least transmission time, reduces internet traffic and collisions
Disadvantages of lossy
Detail is permanently lost
Advantages of lossless
Original quality is preserved
Disadvantage of lossless
Less significant reduction in file size
Example of lossless
Text file
