2.7 Computer Memory

2.7 Computer Memory

1. What is memory?

   • Memory provides the CPU with instructions.
   • ROM and RAM
   • Computer memory only stores data that is currently being used by the CPU.

2. ROM

   • ROM is non-volatile memory so the data is not lost when the computer is powered off.
     • It needs to be non-volatile because the computer must be able to obtain data from the moment the computer is turned on.
   • ROM stores the BIOS. This allows the computer to check:
     • The type of hard disk installed.
     • The amount of RAM installed.
     • The type of CPU being used.
   • The amount of ROM available is normally fixed because this is part of the motherboard.
   • The data cannot be changed by the user. It is 'read-only'.

3. RAM

   • RAM is volatile so anything stored in RAM will be lost as soon as the computer is powered off.
   • RAM is the main place for storing data and instructions while a program is being executed. It is also called main memory.
   • Program data is copied into RAM before the CPU can ruin the program.
   • DRAM
     • DRAM stands for Dynamic Random Access Memory.
     • This needs to constantly receive a refresh signal to keep its capacitors charged otherwise all data will be lost.
     • This is cheaper than SRAM but it has slower access. This is used for RAM.
   • SRAM
     • SRAM stands for Static Random Access Memory.
     • SRAM is more expensive than DRAM however it has faster access.
     • SRAM is used mostly for cache memory since it has faster access.
     • This does not require a refresh signal.