Is cache memory required ?

Banned 9 replies
Found 11th Oct 2010
Hi,
I am currently completing my course work and was wondering if someone could help me with a certain subject. I am writting about memory cache.

As far as i am aware cache stores data to improve the speed of programs and improves the overall system speed however do you require a cache? I havn't found any answer that explain why it is needed, only that it improves the system speed.



Thanks for your time.

Best regards

Joshua

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A processing system requires memory to store program instructions and the results of computations.
Different storage solutions have different access speeds and access to memory store is probably the most significant bottleneck of a processing system.
To increase the overall system speed cache memory is used, this is of a design that has a significantly faster access time than the core memory, it is usually more expensive than core memory.
So you do not need cache for a processing system to operate, however even a small amount of cache will significantly improve system efficiency.

Original Poster Banned

melipona

A processing system requires memory to store program instructions and the … A processing system requires memory to store program instructions and the results of computations. Different storage solutions have different access speeds and access to memory store is probably the most significant bottleneck of a processing system.To increase the overall system speed cache memory is used, this is of a design that has a significantly faster access time than the core memory, it is usually more expensive than core memory.So you do not need cache for a processing system to operate, however even a small amount of cache will significantly improve system efficiency.



Thank you for the reply. You have been very helpful

Just wondering if you know why the processing system cant use the RAM instead? I know it would be much slower, so please can you confirm with yes or no. Do you need a cache memory?

Sorry but I am on a low level course and I would like to learn more


EDIT : I think ive got it. So the processing system doesnt actually require a cache memory.
Edited by: "speedy1477" 11th Oct 2010

A processing system requires memory of one type or another.
Generally cheap memory is slow to access
Fast access memory is more expensive.
so adding cache is a trade off between cost and efficiency
These days fast memory is much more affordable so systems have larger cache.
Early computers did not have the luxury of a cache

Original Poster Banned

melipona

A processing system requires memory of one type or another.Generally … A processing system requires memory of one type or another.Generally cheap memory is slow to accessFast access memory is more expensive.so adding cache is a trade off between cost and efficiencyThese days fast memory is much more affordable so systems have larger cache.Early computers did not have the luxury of a cache



Once again, thanks for your help

different types of devices have different types of cache(some can be referred to as cache memory) i.e. mostly processors, dvd roms, hard drives etc. cahce doesnt just improve speed, the computer is smart enough to place the most frequently accessed files/data so it can be read/write quicker i.e. incoming and outgoing, the bigger the cache the more it can store and remember for fast access.
a hard drive head takes ages going through tracks and sectors etc, the same data in the cache can be accessed without having to waste valuable time and resources finding it on a platter/cylinder of the hard drive.
older processors did not have an inbuilt cache, newer processors do and have lots of other features. i have info on this if your stuck i can go into greater detail ;P.
cache is volatile like ram, only stores data with an electric charge, when power off data lost.

Banned

the main thing you are trying to make use of with computers is processor cycles.
the processor was and still is to an extent the most expensive component of a computer, and for a processor to do it's job it needs access to data.

Data needs to be stored somewhere, the larger capacity the slower the storage usually is (when keeping cost in consideration - added for the pedants)

so while you data may sit on your hard drive, if the processor was accessing the data from the hard drive directly it would miss many cycles waiting for the next bit of data to arrive and the old processed bit of data/information to be stored back to the hard drive.

so they have ram that is faster but more expensive per megabyte to hold data that has just been accessed or is likely to be accessed shortly "in memory"

some operating systems also use "paging" which increases the "virtual ram" by putting aside a set amount of the hard drive to store the data that was just accessed or is likely to be accessed at a lower priority to the data in the real physical ram.

but even ram is too slow for processors these days so they have on board caches, there is L1 and L2 cache and as the memory gets faster it gets more expensive as mentioned before and so the size of the fastest cache is pretty small. like 512kb or 1mb or so, different amounts for different processors.

all of this is in aid of providing the processor with a constant stream of data.


Edited by: "bykergrove" 11th Oct 2010

Original Poster Banned

Thank you bykergrove and andyhunter !

No a processor does not need to have cache - but it speeds things up!

Why you ask?
Well because Hard disks are slow, Ram is faster but still slow compared to onchip memory.

Cache stores EXACTLY the same contents as RAM (only tiny chunks of RAM though), since processors operate on a small amount of data for a along time it's much quicker because it can access the cache much quicker.

Depending on the cache setup (write-back/write-through) the RAM will be updated with the values you have changed in at some point in time.

Wiki:
en.wikipedia.org/wik…che

Being a CS grad from a good uni - I understand these concepts quite well!(_;)

Original Poster Banned

Thanks rash
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