What is the main difference between main memory & cache memory? Explain.?

Question

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Answer 1

The purpose of cache memory is a piece of memory used solely for the purpose of buffering between the RAM and other storage or processing devices (such as video memory, CPU, HD, etc). It has to be fast, theoretically it has to be at least as fast as, or even faster than the main memory (since the RAM is supposed to be one of the fastest among all the devices on the PC). So if there's a cache memory, whenever data is going to be output from the RAM to other devices, it's actually output to the cache memory from the RAM before those data is picked up by other devices. So that the slower device won't slow down the output speed of the RAM, and free up the RAM to handle other tasks, and especially other tasks that require more immediate attention, such as CPU or Video memory.
In order to achieve the purpose of the cache memory, it can be implemented in several different ways. One way is to set aside part of the actual RAM to be used as cache memory, such as video cache memory. If the motherboard design allows, it may allow you to use special faster RAM module to be used solely as cache memory. As for slower cache memory is HD space, such as the Windows swap memory. So what devices are used for the cache memory depends on what purpose of the cache is serving for (between the RAM and what devices).

Answer 2

To put it simply, Cache memory is the memory in-built on to the motherboard and is logically placed between the CPU and the main memory or the RAM. It stores bits of data that it thinks have a greater chance of being used by the CPU and work on the basis of an algorithm. Thus it enhances the speed of processing as the data is more readily available. RAM or main memory, on the other hand is memory that is external to the motherboard and is where the data is stored during processing.

Answer 3

Simply put Main Memory is what you see on your Motherboard. The physical memory chip is called Main Memory. Cache memory is inbuilt in the Processor or Harddisks or whatever and you cannot see them.

Main Memory comes in larger sizes like 256MB, 512MB, 1 GB, etc. Cache Memory is in smaller sizes like 1MB, etc.

Now the main difference. Cache memory is used to provide a suitable interface between devices working at different speeds. Example. we have 512MB RAM or main memory and about 1MB cache in our P4 processors. Now the processor may work at speeds upto 3GHz and so, but the RAM works at a lower speed. The processor needs information stored in the RAM for computations, but the speed at which it works does not match with the RAM speed. Therefore a Cache is put. The cache works at a speed similar to that of the processor. What it does is, some of the recurrent or frequently used information is stored in the cache and the processor uses the information from the cache for its operations. This reduces the amount of time taken for processing by the processor. Any additional information needed is drawn from the RAM.
Cache memory is very expensive when compared to the RAM as the speed is higher therefore we cannot replace our RAM by cache. So some amount of cache memory along with lots of RAM ensures that optimal performance is obtained

Answer 4

Cache memory: only a little of it, really fast access

Main memory: a lot of it, but slower to get to


Think of it this way: cache memory is the random money you have in your pocket, where as the main memory is what you have your wallet. For just buy a can of soda, you're not likely to pull out your wallet. You'd just reach into your pocket and grab a couple coins. However, for bigger amounts you will need to open your wallet.

Computer is about the same. For something accessed frequently, the stuff would be in cache memory, not a lot of it, but it's easily accessed. For a LOT of data, not often accessed, one must go to the main memory.

Answer 5

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