1.2 Memory and storage Flashcards
1.2.1 Primary storage (memory)
The need for primary storage
- low capacity
- internal storage
- directly accesed from the CPU
1.2.1 Primary storage (memory)
RAM vs ROM
RAM:
* volatile (temporary) storage
* stores currently running instructions/data
* able to read and written into
ROM:
* non-volatile
* stores boot program to turn on a computer
* read only memory
1.2.1 Primary storage (memory)
Virtual memory
- using hard disk drive as an extension of RAM for when there is insufficient space on RAM
- unused data in RAM is moved to hard drive, so new & needed data can be put into the RAM
- allows users to run more programs simultaneously with less system slow down
1.2.2 Secondary storage
The need for secondary storage
- non-volatile
- save/stores repeatedly accessed data
- slower to access than primary data - further away from CPU
1.2.2 Secondary storage
Optical storage
- eg: CDs, DVDs, Blu-Ray
- read and write, using lasers
Pros: thin, very portable, cheap
Cons: low capacity, not durable, slowest access speed
1.2.2 Secondary storage
Magnetic storage
- eg: hard disk drive, tape drivers
pros: large capacity, quicker than optical, cheap
cons: not durable, not portable, slow access speed
1.2.2 Secondary storage
Solid state
- eg: solid state drives, USB memory sticks, SD cards
Pros: high capacity, durable, portable, fastest access speeds
Cons: expensive, per gigabyte
1.2.2 Secondary storage
which storage type is the best and worst?
Solid state is the best
Optical is the worst
1.2.3 Units
Storage unit order
- bit
- nibble
- byte
- kilobyte
- megabyte
- gigabyte
- terabyte
- petabyte
Kites Make Great Toy Planes
1.2.4 Data storage - Numbers
Hex, binary, denary conversion
Hex to denary:
* base 16, letter.
* 2A = (2x16)+10 = 42 in denary
Denary to hex:
* 27 = 27/16 = 1r11 = 1B
Binary to hex:
* split into nibble and add and calculate
* 11100101 = 1110 | 0101 = 14 | 5 = 14 +5 = E5
Hex to binary:
* 3B
* 3 = 0011
* B = 11 = 1011
* 3B = 00111011
1.2.4 Data storage - Numbers
Binary shifts
shift left = multiple
shift right = divide
eg: shift right by 3 place:
01010001 = 00001010
cut 3 digits off from the right, replace with 3 0s on the left
shift 1 = effect 2 | shift 2 = effect 4 |shift 3 = effect 8
1.2.4 Data storage - characters
definition of character set
Character set: a table that matches together a character and a binary value.
Necessary as they allow computers to exchange data and humans to input characters
1.2.4 Data storage - characters
ASCII vs Unicode
ASCII:
* doesn’t take much memory
* uses 1 byte to provide 256 characters
* enough for english language, can’t be used for different languages
Unicode:
* uses more memory space
* uses 2 bytes to provide 65,536 characters
* allows different languages and thousand of symbols & emojis
1.2.4 Data storage - images
How is an image presented to a computer?
- as a series of pixels: each pixel has a specific colour, with a specific code
- also represented in binary
1.2.4 Data storage - images
What is metadata
- stores additional image information
- eg: height, width
1.2.4 Data storage - images
What does the quality of the image affect?
and how?
- resolution: higher resolution = less pixelated the image, when zoomed in, it is still clear to see the image
- colour depth: the more colours there are, the more detailed and realistic the image can look
1.2.4 Data storage - images
What does the image size affect?
and how?
- Resolution: the higher the resolution, the higher the file size as there are smaller pixels in a set height/width so more data = higher file size
- Colour depth: if there are more bits to store a colour of a pixel, then there is more data so higher image size
1.2.4 Data storage - images
Formula for file size of images
Resolution x colour depth
1.2.4 Data storage - Characters
Formula for file size of text files
bits per character x number of characters
1.2.4 Data storage - Sound
How can sound be sampled?
The amplitude of the analogue sound wave is measured and recorded in binary at specific intervals
1.2.4 Data storage - Sound
Sample rate
- The number of times per second, the amplitude of the wave is measured
- measured in Hertz
- Higher sample rate = better audio quality because digitial version closely resembles the analogue wave
- Higher sample rate = larger data size because more data is stored
1.2.5 Compression
The need for compression
- makes its file size smaller
- takes less storage space (more files can be stored)
- files can be transferred quicker (since they are smaller)
- files can be read from/written to quicker
1.2.5 Compression
Lossy compression
- reduces file size
- removes data permanently (irreversible)
- quality decreases
1.2.5 Compression
Lossless compression
- file size reduce
- data not permanently removed (reversible)
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