What is Cache Memory

Cache Memory

What is CPU cache? Now a computer has two  different types of memory. One type is what   is used in RAM modules, which is DRAM or a  dynamic RAM. And DRAM is memory that uses  capacitors to store data and these capacitors  have to constantly and dynamically be refreshed often with electricity in order for them  to store data. But there's another type of memory that a computer uses that doesn't have  to be constantly refreshed. And this memory is called SRAM or a static RAM. And SRAM is what is  used in the CPU cache. And because SRAM doesn't have to be constantly refreshed, it is a lot  faster than DRAM and it's also very expensive.The CPU cache is the CPU's internal memory.  And its job is to store copies of data and  instructions from RAM that's waiting to be used  by the CPU. So basically what the CPU cache does, is that it holds common data that it thinks the  CPU is going to access over and over again because  when the CPU needs to access certain data, it  always checks the faster cache memory first to  see if a data it needs is there. And if it's not,  then the CPU would have to go back to the slower primary memory or RAM to get the data it needs. So  that's why cache memory is so important, because  

Cache Memory

if the CPU can access what it needs on the faster  cache, then the faster the computer will perform. So basically the whole idea behind cache is to  make the computer run faster at a cheaper price.  Now a computer can run without the CPU  cache, but it would be a lot slower  because even though RAM is becoming faster,  it still can't feed the data to the CPU fast enough because CPUs have gotten so fast, that  a lot of times the CPU is waiting around doing nothing while it waits for more data, and  this creates a bottleneck. So that's why the CPU cache was developed. So it can  act like a middleman between the CPU and  RAM to assist in feeding the CPU that data it  needs a lot faster which reduces bottlenecks.CPU cache comes in three different  levels. For example there's level 1 cache, which is also called primary cache, and level  1 cache is located on the processor itself. So it runs as the same speed as the processor. So  it's very fast and is the fastest cache on the  computer. And there is also level 2 cache, which  is also called external cache, and level 2 cache  is used to catch recent data accesses from the  processor that were not caught by the level 1  cache. So in a nutshell, if the CPU can't find  that data it needs in the level 1 cache, it then 

Cache Memory

searches the level 2 cache for the data. And if  the CPU can't find the data in the level 2 cache,  then it searches the last level of cache which  is level 3. And level 3 cache is used to catch  recent data accesses that were not caught  by the level 2 cache. And finally if level  3 doesn't have the data, then the CPU has to go  back to the slower RAM to find the data it needs.Now in earlier computers, level 2 cache was  located on a separate chip on the motherboard.  Or in modern CPUs, it would be located on  the processor. Level 2 cache is larger than  level 1 cache but it's not as fast as level  1 cache. And level 3 cache is also located  on the processor. Level 3 is larger than  level 2 but it's not as fast as level 2 cache. Level 3 is often referred to as shared  cache because its memory is shared between all the cores on the CPU, whereas level 1 and level  2 cache are dedicated to their own CPU core.