1.2 Flashcards
Volatile
Memory loses data once power is turned off
RAM vs ROM (4 differences)
RAM:
- Volatile
- Stores currently running programs temporarily
- Data can be changed
- Big compared to
ROM:
- Non-volatile
- Stores boot-up instructions
- Data cannot be changed
- Small compared to
Primary Storage Examples
- RAM
- ROM
- Registers
- Cache
Primary Storage
- Temporarily holds data and instructions which CPU needs access to while computer is running
- Can access data faster than secondary
- Volatile
Virtual Memory
- Needed when not enough physical RAM to store opened programs
- Space on hard disk
- Transferred out to VM from RAM if not currently being executed
- Transferred back to RAM from VM when needed
Secondary Storage
- Needed since ROM is read only and RAM is volatile
- Long term storage of programs and data when power is turned off
- Backup of data files
- Archive of data files
Types of Secondary Storage
- Optical (CDs/DVDs/Blu-Ray)
- Magnetic (Hard disk drive)
- Solid State (SSD, Memory sticks, Flash memory cards)
Optical (3)
- Low storage capacity compared to
- Slow access
- Thin, lightweight, portable
Magnetic (4)
- High storage capacity
- Quick access
- Moving parts which eventually fail
- Perform better if defragmented
Solid State (8)
- Medium storage capacity
- Very quick access
- No moving parts, reliable
- Low power
- No noise
- No need to defragment
- Limited R/W cycles
- Relatively expensive
Units of data capacity
- Bit (b)
- Nibble
- Byte (B)
- Kilobyte (KB)
- Megabyte (MB)
- Gigabyte (GB)
- Terabyte (TB)
- Petabyte (PB)
Characteristics that should be considered when choosing secondary storage (6)
- Capacity
- Speed
- Portability
- Durability
- Reliability
- Cost
Explain why computers use binary
- Ideal for representing two states (on or off), simple for computers to process data efficiently
- Operate with switches that have only two states
With two states, electronic components are: (3)
- Easier to manufacture
- Cheaper
- More reliable
Text Files Calculation
Bits per Character x Number of Chararacters
Sound Files Calculation
Sample Rate x Duration (s) x Bit Depth
Image Files Calculation
Colour Depth x Image Height (px) x Image Width (px)
Character Set
- Defined list of characters recognised by the computer
- Each character is represented by a unique binary number
ASCII, Extended ASCII, UNICODE
- ASCII: 2^7
- Extended ASCII: 2^8
- UNICODE: 2^24
What can images stored in binary be?
- Bitmaps: constructed from coloured squares (pixels)
- Vectors: store the mathematics to draw coloured shapes
What are pixels stored as?
Binary
How can the number of colours be calculated?
- 2^n
- n is the number of bits per pixel
What is number of bits per pixel known as?
Colour depth
What results in a larger file size of an image?
- Greater colour depth
- Greater resolution (width x height)
Metadata + Examples (7)
Additional data about the file saved
- Type of file
- Data of creation
- Creator of data
- File size
- Dimensions
- Image resolution
- Colour depth
What is the Analogue-to-Digital Converter (ADC)?
- Sound sampling device
- Converts real-world analogue signals (sound waves) to a digital representation
Bit Depth
- Number of bits needed to store each sample
- Higher number of bits = greater quality of sound = larger file size
Sample Rate
- Frequency the sound wave is measured per second
- Higher samples per second = higher quality = larger file size
Sample
Measure of amplitude at a point in time
Why is compression used?
- Reduces size of file
- Takes up less space
- Maximises amount of data that can be stored on a device
- Quicker when transferred over the Internet
Lossy Compression (4)
- Data is lost and cannot be recovered
- Greatly reduces file size
- Reduces quality of image/sound
- Suitable for images, sound and video
Lossless Compression (4)
- No data is lost, encoded differently
- Can be reverted into original format
- Less effective in reducing file size
- Suitable for documents and executable files (can be used in all though)
Overflow
- Calculation producing an answer that has more bits than the CPU was expecting
- Leads to an inaccuracy
