1.2 Flashcards
What does volatile mean?
- Data in memory is lost when power is turned off
What are the differences between RAM and ROM?
RAM:
- Volatile
- Stores currently running instructions and data temporarily
- Data can be changed
- Big compared to
ROM:
- Non-volatile
- Read only (data cannot be changed)
- Stores boot-up instructions (bootstrap)
- Small compared to
Give some examples of primary storage
- RAM
- ROM
- Registers
- Cache
What is primary storage?
- Temporarily holds data and instructions which CPU needs access to while computer is running
- Can access data faster than secondary
- Volatile
What is virtual memory?
- Part of hard disk is used as an extension when RAM is nearly full
- Allows more applications to be open at once
- Transferred out to VM from RAM if not currently being executed
- Transferred back to RAM from VM when needed
What is secondary storage?
- Needed since ROM is read only and RAM is volatile
- Long term/permanent storage of programs and data when power is turned off
- Backup of data files
- Archive of data files
- Read and write
State the three types of secondary storage
- Optical (CDs/DVDs/Blu-Ray)
- Magnetic (Hard disk drive)
- Solid State (SSD, Memory sticks, Flash memory cards)
What is optical storage?
- Used for music, films and archive files
- Low storage capacity compared to
- Slow access
- Thin, lightweight, portable
- Prone to scratches
- Cheap
What is magnetic storage?
- Used to store operating system and application
- High storage capacity
- Quick access
- Moving parts which eventually fail
- Low portability
- Medium cost
- Reliable but not durable
- Perform better if defragmented
What is solid state storage?
- Used for digital cameras and smartphones
- Medium storage capacity
- Very quick access
- No moving parts, reliable and durable
- Low power
- No noise
- No need to defragment
- Limited R/W cycles
- Relatively expensive
What are the units of storage from smallest to largest?
- Bit (b): binary digit (0 or 1)
- Nibble: 4 bits/half a byte
- Byte (B): 8 bits, can represent one ASCII character
- Kilobyte (KB): 1 thousand
- Megabyte (MB): 1 million
- Gigabyte (GB): 1 billion
- Terabyte (TB): 1 million million
- Petabyte (PB): 1 thousand million million
Mnemonic for data units
Burger King Makes Great Toast, Perfect
What are the characteristics that should be considered when choosing secondary storage?
- Capacity
- Speed
- Portability
- Durability
- Reliability
- Cost
Why do 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
- RAM: charge or no charge
- CD/DVD: pit or land
With two states, electronic components are:
- Easier to manufacture
- Cheaper
- More reliable
How do you calculate text files?
Bits per Character x Number of Chararacters
How do you calculate sound files?
Sample Rate x Duration (s) x Bit Depth
How do you calculate image files?
Colour Depth x Image Height (px) x Image Width (px) + 10% for metadata
What is a 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 (7 bits)
- Extended ASCII: 2^8 (8 bits)
- UNICODE: 2^24 (24 bits)
What can images stored in binary be?
- Bitmaps: constructed from coloured squares (pixels)
- Vectors: created using mathematical equations to draw 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 colour depth?
- Number of bits used to indicate the colour of a pixel
What results in a larger file size of an image?
- Greater colour depth
- Greater resolution (width x height)
What is resolution?
- Number of pixels contained on a display monitor
- Number of pixels on x axis times number of pixels on y axis
What is metadata? Give examples
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
What is bit depth?
- Number of bits needed to store each sample
- Higher number of bits = greater quality of sound = larger file size
What is sample rate?
- Frequency the sound wave is measured per second
- Higher samples per second = higher quality = larger file size
What is a 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
What is lossy compression?
- Data is lost and cannot be recovered
- Greatly reduces file size
- Reduces quality of image/sound
- Suitable for images, sound and video
What is lossless compression?
- 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)
What is arithmetic overflow?
- Calculation producing an answer that has more bits than the CPU was expecting (insufficient bits to store)
- Due to final carry bit
- Leads to an inaccuracy
How to convert hexadecimal to denary?
- Digit 1 * 16 + Digit 2
