Memory

Memory

1. RAM

   • RAM: The main memory of a computer
   • RAM or Random Access Memory is used as the main memory in a computer
   • Can be read and written to
   • RAM is volatile
   • Volatile: Volatile Memory is temporary memory. It requires power to retain its data
   • When a computer boots up, the operating system is copied from secondary storage to RAM
   • When software applications, documents and files are opened, they are copied from secondary storage to RAM. They stay in RAM until the files or applications are closed
   • Slower than CPU cache, but way faster than secondary storage

2. ROM

   • ROM: Memory that can be read but not written to
   • ROM or Read Only Memory is non-volatile
   • ROM comes on a small, factory made chip built into the motherboard
   • BIOS: Basic Input/ output System
   • Non-Volatile: Non-Volatile: Non-Volatile is permanent memory- it keeps its contents even when it has no power
   • As soon as the computer is powered on, the CPU reads the instructions from ROM. This tells the CPU to perform self checks and set up the computer

3. Virtual Memory

   • Virtual Memory: Area of secondary storage used by the OS (Operating System) as extra Ram
   • When RAM is full it moves data that hasn't been used recently to a location of secondary storage called Virtual Memory
   • Virtual Memory may be needed if there are too many applications open at once, or if a particular memory is being used
   • If the CPU needs to read data stored in virtual memory, it must move the data back to RAM. This is slow as data transfer rates are much slower on secondary storage than RAM
   • Using virtual memory can make a computer slow to respond when switching between aplications

4. Flash Memory

   • Flash Memory: This is memory which can be programmed electrically but then keeps its data when the power is turned off
   • Data can be stored electrically using flash memory
   • Flash memory was developed from a type of ROM called 'electrically erasable programmable read-only memory' (EEPROM) and was introduced in 1984
   • EEPROMs had to be completely erased before they could be written to, but flash memory can be written and read in small blocks
   • Flash Memory is used in SD cards, Micro SD cards, SDXC cards and USB flash drives
   • Used for data storage in cameras, mobile phones and embedded devices and increasingly as the main secondary storage device in computers, especially in laptops as solid state drives
   • Flash memory devices are ideal for transporting as they are light and being solid state have no moving parts which could be damaged