1.2 Memory

1.2 Memory

1. ROM

   • Non Volatile form of memory
   • Retains its information through power off
   • Contains data that is pre-written and permanently written on a ROM chip
   • The location of the POST sequence
     • Power On Self- Test
       • BIOS chip performs checks
       • Makes sure components are present and fuctional
       • Once completed successfully, the OS boots up
     • Uses the BIOS instructions
       • Basic Input Output System
   • Considered as permanent
   • Read-Only Memory

2. RAM

   • A volatile form of memory
   • Loses its information at power off
   • Contains the data and programs currently in use
   • Can be DRAM or SRAM
     • DRAM - Dynamic RAM
       • Slower as needs to be refreshed thousands of times per second
       • Cheaper and so more common
     • SRAM - Static RAM
       • Faster as doesnt need to refresh
       • Expensive and Less Common
   • Random Access Memory

3. Flash Memory

   • Can be easily broken
   • Relatively Cheap
   • Examples include USB drives and Memory Cards
   • Can very easily be broken and/or stolen
   • Can be used to back up computational data

4. Virtual Memory

   • A simulated form of memory found on the hard drive
   • Created by the Operating System (OS)
   • It is needed to make more memory than is actually in the system
   • It's needed when you need to run things that RAM can't support.
   • Data must be in RAM before it can be processed by the CPU
     • Data is swapped between RAM and Virtual Memory if RAM is low
       • Can slow computer down if needing to use Virtual Memory ... better to add more RAM

5. Registers within a computer

   • See 1.1 Revision Map

6. Disc Thrashing - The process the system uses to move data between Virtual Memory, RAM and Cache.

   • Depends on the frequency of the data, how often it's used.