Cache memory provides faster data storage and access by storing instances of programs and data routinely accessed by the processor. Thus, when a processor requests data that already has an instance in the cache memory, it does not need to go to the main memory or the hard disk to fetch the data.
Cache memory is the fastest memory available and acts as a buffer between RAM and the CPU. The processor checks whether a corresponding entry is available in the cache every time it needs to read or write a location, thus reducing the time required to access information from the main memory.
Hardware cache is also called processor cache, and is a physical component of the processor. Depending on how close it is to the processor core, can be primary or secondary cache memory, with primary cache memory directly integrated into (or closest to) the processor.
Speed depends on the proximity as well as the size of the cache itself. The more data can be stored into the cache, the quicker it operates, so chips with a smaller storage capacity tend to be slower even if it’s closer to the processor.
In addition to hardware-based cache, cache memory also can be a disk cache, where a reserved portion on a disk stores and provides access to frequently accessed data/applications from the disk. Whenever the processor accesses data for the first time, a copy is made into the cache.
When that data is accessed again, if a copy is available in the cache, that copy is accessed first so the speed and efficiency is increased. If it’s not available, then larger, more distant, and slower memories are accessed (such as the RAM or the hard disk).
Modern video cards also store their own cached memory inside their graphics processing chips. This way, their GPU can complete complex rendering operations more quickly without having to rely on the system’s RAM.
Other than hardware cache, software cache is also available as a method to store temporary files on the hard disk. This cache (also known as browser or application cache) is used to rapidly access previously stored files for the same reason: increasing speed. For example, an online browser might save some images from a web page by caching them to avoid re-downloading them every time that page is open again.
Advantages
The advantages of cache memory are as follows −
- Cache memory is faster than main memory.
- It consumes less access time as compared to main memory.
- It stores the program that can be executed within a short period of time.
- It stores data for temporary use.
Disadvantages
The disadvantages of cache memory are as follows −
- Cache memory has limited capacity.
- It is very expensive.
Basic Operations of Cache Memory
Its basic operations are as follows:
- The CPU first checks any required data in the cache. Furthermore, it does not access the main memory if that data is present in the cache.
- On the other hand, if the data is not present in the cache then it accesses the main memory.
- The block of words that the CPU accesses currently is transferred from the main memory to the cache for quick access in the future.
- The hit ratio defines the performance of the cache memory.
Levels of Cache Memory
There can be various levels of cache memory, they are as follows:
Level 1 (L1) or Registers
It stores and accepts the data which is immediately stores in the CPU. For example instruction register, program counter, accumulator, address register, etc.
Level 2 (L2) or Cache Memory
It is the fastest memory that stores data temporarily for fast access by the CPU. Moreover, it has the fastest access time.
Level 3 (L3) or Main Memory
It is the main memory where the computer stores all the current data. It is a volatile memory which means that it loses data on power OFF.
Level 4 (L4) or Secondary Memory
It is slow in terms of access time. But, the data stays permanently in this memory.
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Types of Cache Memory
There are two types, as follows:
Primary Cache
It’s located on the processor chip always. Besides, its access time is comparable to the processor.
Secondary Cache
This memory is present between the primary cache and the main memory. Besides, we can also call it level 2 (L2) cache.
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