Memory

Memory

1. ROM

   • Contains BIOS
   • Can't be written to easily
   • "Read Only Memory"
   • Required for startup
   • Non-volatile
   • Small capacity (normally KB's)
   • Located on the motherboard

2. RAM

   • "Random access memory"
   • Relatively large capacity (normally GB's)
   • Can be written to easily
   • Holds programs and data currently in use
   • Easily upgradable
   • When full, data is sent to virtual memory
   • Located on the motherboard
   • Data can be accessed in any order
   • Can be edited unlike ROM
   • CPU fetches instructions from RAM
   • When RAM runs out, performance is reduced
   • Can also be referred to as "main memory"
   • Faster to access than secondary storage

3. Virtual memory

   • Slower than RAM
   • Data is moved automatically when RAM is full
   • Memory space inside main storage
   • Holds more data and instructions for programs in use
   • Used when RAM is full
   • Volatile
   • Data is located in RAM before being moved to virtual memory
   • Allows more programs to be run
   • Disk thrashing can occur
   • Less used data is moved here

4. Volatile memory

   • Data is lost without power
   • Must constantly be powered
   • Includes memory such as RAM, registers, and cache
   • Secondary storage is non-volatile and main memory is volatile (except for ROM)

5. Cache

   • Level 1 - Fastest but smallest capacity
   • Level 3 - Slowest but largest capacity
   • Level 2 - Medium speed and medium capacity
   • Extremely fast (fastest memory apart from registers)
   • Very small capacity
   • Used to store frequently used programs and data
   • Much more expensive to upgrade than RAM
   • Faster cache levels are located inside the CPU, slower cache levels are located on the motherboard

6. SRAM

   • Static Random Access Memory
   • Used in cache
   • More expensive than DRAM
   • No new signal required all the time
   • Faster to access than DRAM
   • Non-volatile

7. DRAM

   • Requires fresh signal to retain data
   • Volatile
   • Used in RAM modules
   • Dynamic Random Access Memory
   • Less expensive than SRAM
   • Slower to access than SRAM