Computer Memory

Objectives...•What is RAM & ROM?

•What are their features?

•What are their differences?

•What do the terms volatile/non-volatile mean?

•What is rom used for?

•What is RAM Used for?

•How can RAM affect performance?

Objectives...• i) Describe the difference between RAM and ROM

• ii) Explain the need for ROM in a computer system

• iii) Describe the purpose of RAM in a computer system

• iv) Explain how the amount of RAM in a personal computer affects the performance of the computer

Memory•The Central Processing Unit (CPU) needs to store

data whilst it is carrying out the processing required.

•The hardware that carries out this task is called 'memory'. Memory can be classed into two types:

•Read Only Memory (ROM)

•Random Access Memory (RAM)

ROM•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).

•It allows it to check the type of hard disk installed, the amount of memory installed, the type of CPU being used etc.

ROM•ROM is a type of memory that 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.

•It is non-volatile

ROM•Because the data is 'read only', it can be read

but not changed by the user.

•The ROM chip (although there may be more than one) is attached to the Motherboard.

•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.

RAM•How many times has the computer

crashed or your mate 'accidentally' switched it off.?

•When you rebooted and logged back in, your work was gone forever.

RAM•This was because your work was stored in

RAM, or 'temporary memory'.

•It was fairly safe there while the computer was working, but as soon as it was switched off, everything disappeared.

•This type of memory known as 'volatile memory'.

RAM•As well as storing the data you are

working on, RAM also stores the modules that are needed to make your applications work.

•For example, when you open up your favourite word processing application, you may notice a short delay while the modules are loaded into RAM.

RAM•RAM is also needed so that you can

have multiple windows open and so that you can switch between them.

RAM•However, if you have a lot of windows,

documents and different applications running, you might find that your system starts to slow down.

•This is because your RAM is full up and it is having to decide what it needs to keep stored in memory at any given time and what it can release.

RAM•If this happens to you a lot, you can

improve the performance of your computer by installing extra RAM.

Performance•It was mentioned that data and

programs are stored in RAM, ready for use by the CPU.

•But there is only a limited amount of RAM available in any computer system.

Performance•What happens when there is so much being

used that you run out of memory?

•Answer: the computer stops running or 'crashes'.

•The more memory you have available the more applications you can have open at the same time.

Performance•Operating Systems like Windows can be

clever and work around this.

•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'.

Virtual Memory•You must have enough RAM installed in the

computer to run the applications you intend use.

•This minimum is usually stated on the side of the box it came in.

•Even the operating system has to have a minimum amount of RAM for it to run.

Virtual Memory

Virtual Memory

Virtual Memory

Virtual Memory