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.

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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.

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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

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Running out of RAM?

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

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Total memory in use

Hard disk

RAM

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.

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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

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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

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Task 1:

• Using Publisher or Word, create an A4 revision poster about the topic of Memory. You must include– RAM– ROM– Cache– Virtual

You may use the internet for research and images.

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Key Words

• Processor• Random Access Memory• Read Only Memory• CPU• Data• Volatile• Permanent

MEMORY

MEMORY

ROM• Holds the boot up programs • Runs as soon as the computer is turned

on• Is non volatile, so it won’t be lost when

there is no power• Usually quite small in capacity

RAM• Holds data on the programs that are

running• Is volatile, so it is lost when the power

is turned off• 4GB standard for laptops• The more RAM the better the

performance

Cache• Located on the processor• Small compared to RAM• Much quicker than RAM but much

more expensive• Used to hold data that is used a lot

Virtual• Used when running out of RAM• Uses a section of the harddrive to

temporarily store data on programs• Takes longer than accessing RAM, so

not a permanent solution