A faster and smaller segment of memory whose access time is as close as registers is known as Cache memory. In a hierarchy of memory, cache memory has access time lesser than primary memory. Generally, cache memory is very smaller and hence is used as a buffer.
Need of cache memory
Data in primary memory can be accessed faster than secondary memory but still, access times of primary memory are generally in few microseconds, whereas CPU is capable of performing operations in nanoseconds. Due to the time lag between accessing data and acting of data performance of the system decreases as the CPU is not utilized properly, it may remain idle for some time. In order to minimize this time gap new segment of memory is Introduced known as Cache Memory.
How does cache work?
In order to understand the working of cache we must understand few points:
- Cache memory is faster, they can be accessed very fast
- Cache memory is smaller, a large amount of data cannot be stored
Whenever CPU needs any data it searches for corresponding data in the cache (fast process) if data is found, it processes the data according to instructions, however, if data is not found in the cache CPU search for that data in primary memory(slower process) and loads it into the cache. This ensures frequently accessed data are always found in the cache and hence minimizes the time required to access the data.
- On searching in the cache if data is found, a cache hit has occurred.
- On searching in the cache if data is not found, a cache miss has occurred.
Performance of cache is measured by the number of cache hits to the number of searches. This parameter of measuring performance is known as the Hit Ratio.
Hit ratio=(Number of cache hits)/(Number of searches)
Types of Cache Memory
L1 or Level 1 Cache: It is the first level of cache memory that is present inside the processor. It is present in a small amount inside every core of the processor separately. The size of this memory ranges from 2KB to 64 KB.
L2 or Level 2 Cache: It is the second level of cache memory that may present inside or outside the CPU. If not present inside the core, It can be shared between two cores depending upon the architecture and is connected to a processor with the high-speed bus. The size of memory ranges from 256 KB to 512 KB.
L3 or Level 3 Cache: It is the third level of cache memory that is present outside the CPU and is shared by all the cores of the CPU. Some high processors may have this cache. This cache is used to increase the performance of the L2 and L1 cache. The size of this memory ranges from 1 MB to 8MB.
Cache vs RAM
Although, Cache and RAM both are used to increase the performance of the system there exists a lot of difference in which they operate to increase the efficiency of the system. RAM Cache
RAM is larger in size compared to cache. Memory ranges from 1MB to 16GB The cache is smaller in size. Memory ranges from 2KB to a few MB generally. It stores data that is currently processed by the processor. It holds frequently accessed data. OS interacts with secondary memory to get data to be stored in Primary Memory or RAM OS interacts with primary memory to get data to be stored in Cache. It is ensured that data in RAM are loaded before access to the CPU. This eliminates RAM miss never. CPU searches for data in Cache, if not found cache miss occur.
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