In this article, we guide you how cache memory works. We tell you about cache memory size, cache memory speed and a lot more. Read the Full article here.
Generally, There are three types of memory present in our computer. Those are General Hard Disk Drive or Solid State Drive, RAM and finally, Cache Memory. General Hard Disk Drive or Solid State Drive (HDD or SSD is used to store general files or data you used in your day to day life). RAM (RAM is the Second Fastest memory use to store programs that you install on your computer). Cache Memory (It is fastest but it is very less in terms of capacity)
Cache Memory Introduction
System on Chip designers facing several issues due to slow memory i.e. RAM or Hard Disk etc. Sounds Weird when we say that RAM is slow. But hold on for a sec. Didn’t you know that speed is relative? This Principle applies here too. When we compare the speed of RAM with relative to Hard Disk Drive then, we can say that, the speed of RAM is faster with respect to Hard Disk Drive. But when we compare its speed with Cache, then it is not the case. Because, in this case the transfer speed of RAM falls down.
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How Cache Memory Works
How Cache Memory Work Explanation: When a Processor requests some data from the RAM, it has to wait for while before the data is being fetch. So, Very first, here the time utilization gets limited. In modern day PC, the processor uses 4 to 8 or even 12 cores for processing the data inside the computer. These all cores access the memory (or more conveniently RAM) at a same time but they can’t because only one core can access it at one time. Because of this, the processor performance gets limited. This situation is popularly known as VON-NEUMANN BOTTLENECK. A situation in which the processor performance gets limited due to relative speed difference between processor and RAM.
How the issue gets resolved?
This issue is further resolved by the introduction of Cache in the Tech Industry. Cache is a very fast memory whose speed is almost equal to the speed of the processor. The idea implanted was that, there is no direct data transfer between RAM and Processor. The Data transfer between them occur through Cache. Next, Every core of a processor, has it’s own cache, so that the VON-NEUMANN BOTTLENECK doesn’t happen here also. A cache for a core means that, Suppose if we have an Octa Core Processor then we have 8 cache one for each. By applying this they reduce the relative speed time differential between the processor and RAM and Finally, VON-NEUMANN BOTTLENECK doesn’t occur.
Cache Memory types | Cache Memory Splitting
Time goes on and further enhancement occurs. Now, SOC Designers further improve the cache by strictly dividing it into two parts. The first part was named as Instruction Cache and the second part was Data Cache. The Instruction Cache contains some list of data that are executed in past and might be executed in future. Whereas, The data cache works as usual like a faster memory transferring platform between processor and RAM.
The Designers further improve the Cache by introducing the Cache Hierarchy Technique. Here they Create levels of Cache or more conveniently classified it as types of cache as follows:
- Level 1 Cache: This is the fastest type of cache which is present inside the core.
- Level 2 Cache: This Cache is present on the same IC (Integrated Circuit) Board where core is present. Moreover, A high speed bus is assembled between this cache and the core for high speed data transmission.
- Level 3 Cache: This type of Cache is shared among all the cores present inside the processor. It’s speed is Faster than RAM but Slower than Level 2 Cache.
As we know, Our processor is composed of several cores. For every core, two cache memory is separate i.e. Level 1 and Level 2. But the third type of cache memory i.e. Level 3 is shared between all the cores.
How Data Transfer Occurs through Cache Memory?
First, the processor search the data in the L1 Cache, Instruction Cache Section. If the data isn’t present there, then processor access the L2 Cache Instruction Cache Section through the L1 Data cache. Furthermore, if the data again not present in L2 Cache Instruction Cache Section, then the processor access the L3 Cache Instruction Cache Section with the help of L2 Cache Data Cache Section. Again if, data is not present in L3 Cache Instruction Cache Section, then the processor access the RAM with the help of L3 Cache Data Section.
Cache Memory Speed
Cache Memory Speed lies between 25 MHz to 5GHz. It depends on the CPU speed means if we have 3GHz Core 2 CPU then, we get 3GHz Cache memory speed. The Cache Memory Speed also depends on Several other factors like what kind of RAM Chip is used to manufacture the cache memory. There are two types of RAM Chips: SRAM (Static RAM Chip) & DRAM (Dynamic RAM Chip). SRAM is faster & expensive relative to DRAM. So, the Cache Memory made of SRAM is faster and expensive and so on. The Speed of SRAM and DRAM is measured in nanoseconds. On average, SRAM gives a speed of 7 to 20 ns whereas DRAM gives speed between 50 to 70 ns.
Cache Memory Size
In modern day computers a typical Level 2 cache memory size can be 256KB, 512KB, 1MB or even 2MB. Whereas Level 1 cache memory size lies between 8KB to 64KB. Level 3 Cache memory size lies between 2MB to 12MB in todays computers.
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