MEMORY

Or am I ROM?

Am I RAM

MEMORY

I’m volatileI’m non-volatileI’m read-onlyMy content changesall the time

I’m small. Only around 1 or 2 MB

An average laptopHas around 4GB of me

I contain the boot program

I contain the operatingSystem, programs and

data that isBeing used.

MEMORY

Lesson Objectives

• explain the need for virtual memory• describe cache memory• describe flash memory

MEMORY

HP Desktop Computer

• 6MB Cache• 8GB RAM

£500

MEMORY

Cache Memory

• Cache memory is memory that is located on the processor itself and is used to make the computer faster.

• The cache memory acts as a buffer between the CPU and the RAM.

MEMORY

Cache Memory

CPU Cache RAM

The CPU request data

If the data is not in the Cache It requests the data from the RAM

Data copied to the CacheData sent to CPU

If the CPU then requests the same piece of data again, it will already be stored in the cache. This makes the process quicker as it does not have to go to the RAM

MEMORY

• The transfer between the cache memory and the main processor is much faster than the transfer between the RAM and the cache memory.

• When the processor tries to fetch the data again, it first checks whether the data is already in the cache memory. If it is, then the data is fetched from the cache memory and not from the RAM. This way, by storing the data that is fetched most often so that it does not need to be fetched from the RAM, the cache memory makes the whole system a lot faster.

• The larger the cache memory, the more the improvement in performance will be. For this reason, modern processors include up to 8 MB or more of cache memory.

MEMORY

Why don’t we always use the cache for everything?

• Because it’s much more expensive.

• This is why you often have a small cache compared to the amount of RAM

MEMORY

Running out of RAM?

• Have you ever been using a computer and the message “You are low on virtual memory, please close some applications”?

MEMORY

Virtual Memory• When there is not enough RAM to deal with all the

demands on the computer it will use a section of the hard disk as a temporary store. This is called VIRTUAL MEMORY.

• The computer can take some programs out of the RAM and store them in a reserved part of the hard drive which frees up some RAM that can be now be used to open more programs.

• When any of the programs that have been transferred to the hard disk are needed again, they need to be transferred back into the RAM before they can be used

MEMORY

OCR GCSE Computing © Hodder Education 2013 Slide 11

Total memory in use

Hard disk

RAM

Virtual Memory space on hard disk

MEMORY

Virtual Memory

• Virtual memory is not a permanent solution.

• The time taken to access the hard disk on a computer is significantly longer than that required to access RAM.

• If a computer is having to move data between the hard disk and RAM constantly, it will slow down the computer significantly

MEMORY

How can you speed up your computer?

• Exit some programs

• Add extra RAM to allow more programs to run

MEMORY

Flash Memory

• Flash memory is used as a removable form of memory.

• How many different types of removable memory can you think of?– USB memory stick– Memory cards in cameras, phones– Mini and Micro SD cards