Memory The CPU in the computer fetches data and instructions from memory to process. This type of memory is called primary memory and it is the only memory the CPU can access directly. The two main types of primary memory are RAM( Random Access Memory) and ROM (Read Only Memory)

RAM RAM is memory that can be accessed and changed by the computer at any time. RAM stores the programs and data that the computer is currently working on. The operating system will also be loaded into RAM in order to run. RAM needs power to store data and is volatile (i.e. if you turn off the power everything in RAM is lost) Data is stored in RAM as a charge in an electronic circuit and will leak away if not kept refreshed.

RAM – What’s in it? If you are listening to some music while researching on the internet for information to use in a word processed document, the RAM might contain: The operating system for the computer Music player software The music file you are listening to The web browser software The website you are looking at The word processor software The word-processed file Anti-virus software

RAM What happens if you run out it? Answer: the computer stops running or 'crashes‘ unless the operating system deals with It intelligently . the operating system uses some clever tricks to make part of the hard disk appear as extra RAM. This is called 'virtual memory'. But it is very slow compared to 'real' RAM and so the operating system may give a warning such as 'you are low on virtual memory, please close some applications'. Question – What will adding more RAM do to the computer’s performance? Adding more RAM to a computer will improve the performance of that computer How does it do this? by making more memory available for direct access from the CPU.

RAM Does it always have something in it? When the computer is first switched on RAM will be empty because it is volatile and needs power to maintain the contents. In order to supply the instructions needed to start up the computer, the CPU needs access to permanently stored instructions, the boot program.

ROM What is it? ROM is a special kind of memory which stores the instructions which the computer uses when it 'boots up' - the BIOS (basic input output system). The key thing to remember about ROM is that the data is not erased when the computer is switched off - the data is stored permanently. This type of memory is also called 'non volatile memory' Can you lose the information stored in it? Can you change what is stored in it? Because the data is 'read only', it can be read but not changed by the user. ROM retains its data even without power, so even when the computer is switched off, it will not lose the data which is saved onto it.

ROM Many devices, including music players, mobile phones and cameras, need ROM to boot them up. Since many of these devices have the operating system stored in ROM, the type of ROM used is changeable through a process called ‘flashing’, hence flash memory.

Sum it up RAM ROM Contents Operating system, programs and data in use by the CPU The boot program used to start and set up the computer Volatile? Yes No Size Typically quite large, e.g. 8GB. More RAM enables the computer to work on more things at once Usually quite small just to store the boot program, 1 or 2 MB Can contents be changed? Yes, contents change all the time while the computer is running Not normally but can be changed by a special ‘flashing’ operation