OCR - GCSE - Computer Science - Memory

OCR - GCSE - Computer Science - Memory

1. Random Access Memory (RAM) and Read Only Memory (ROM)

   • RAM
     • RAM is a type of computer memory where the computer stores data and instructions when an application is running.
     • Positive: Data can be read from and written to RAM.
     • Negative: RAM is volatile - if you turn off the power; data in RAM is lost.
   • ROM
     • ROM is a type of memory that is used to store instructions that don't need to be changed during normal use.
     • Positive: Data can be read from ROM.
     • Negative: ROM is non-volatile - it retains data even if the power is turned off.

2. Virtual Memory

   • Virtual Memory is an area of the hard disc or solid-state drive used as temporary RAM when the actual RAM is full.
   • Disadvantages: The read / write speed of magnetic hard drive is much slower than RAM. There will be a significant performance drop if the system has to rely too heavily on virtual memory.
   • Disadvantages: If the OS is constantly swapping between RAM and the hard disc drive, programs will run more slowly. This is called disc thrashing.
   • A computer uses virtual memory by moving to the least recently used instructions and data into the main memory. This allows other data to be loaded into the main memory. A computer uses virtual memory to compensate for not having a sufficient amount of RAM.
   • Usually the least recently used stored data is swapped out.
     • If data is swapped out and is then needed again, it is swapped back in from the virtual memory at the expense of other data.
       • The more RAM a computer has then the less virtual memory will be needed.
         • Adding more RAM will significantly improve the performance of a computer.
   • Positive: An advantage of virtual memory is that program operation will continue even when the main memory is full.