Computer addressability: 

Addressability is the way in which the computer identifies different memory locations. Each memory location has a unique address, meaning it is one of a kind.

Memory:

There are 2 main types of memory:

  • Main memory (aka primary memory) is held on chips. 
  •  Backing storage (aka secondary memory) is not part of the computers main memory.

The size/width of the address bus determines how many memory locations can be accessed.  For example –  a 1 bit address bus can access 2 memory locations,  a 2 bit address bus can access 4 memory locations and a 3 bit address bus can access 8 memory locations etc.

To calculate the total addressable memory of a computer, use this equation:

The number of storage locations x the size of each storage location

Each storage location holds one word.

There are 5 main types of memory:

  • RAM
  • ROM
  • Cache
  • Registers
  • Virtual

There are 3 types of  ROM memory:

  • Programmable ROM (PROM) –  This type of ROM has no pre-written data on it and is empty so that the user can program it, however, once written, the data cannot be erased.
  • Erasable PROM (EPROM) – This is the same as PROM except it can be removed from the computer, have it’s data erased and have another put in it’s place using Ultra-Violet light.
  • Electrically EPROM (EEPROM) – The same as EPROM except electricity is used to erase and re-write selected contents.

There are 2 types of RAM memory; Static RAM (SROM) and Dynamic RAM (DRAM). SRAM has faster access speeds than DRAM, however the processor mainly uses DRAM as it is more simple to use and it also uses less power.

Cache memory is physically built into the processor, which is placed closer to the processor than RAM. This memory is used to store the next instructions which are going to be read by the computer.