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The main content of this article is to explain "what is the role of caching in SSD". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Now let the editor take you to learn "what is the role of caching in SSD?"

With the popularity of SSD solid state drives, the price of SSD with cache is gradually accepted by users. Although we know that SSD without cache will be slightly more expensive than those with cache, it is not true what role cache plays in SSD solid state disk.

With the popularity of SSD SSDs, the price of SSD with cache is gradually accepted by users. Although we know that SSD without cache will be slightly more expensive than those with cache, not everyone knows exactly what role cache plays in SSD SSDs.

In fact, the word "cache" can be interpreted literally as deferred storage. Simply put, "cache" exists to balance the speed difference between high-speed devices and low-speed devices. The function is to keep the low-speed equipment from dragging back the high-speed equipment as much as possible. The word "as far as possible" is used here, mainly because the cache capacity in various products is limited, and the algorithm cannot be hit 100% accurately, so low-speed devices will more or less hinder high-speed devices. The role of cache can only be "as far as possible" to reduce this phenomenon.

For example, CPU cache; whenever CPU reads data from memory, it will send a read instruction to the memory controller, asking the memory controller to return the required data, but because the memory response speed is very slow relative to CPU, CPU only has nothing to do "wait" before data return, if this often happens, no matter how fast CPU will be held back by memory, the efficiency will not be improved.

As shown in the figure, put a small SRAM between the main memory (RAM) and the CPU. When CPU applies for RAM data, look for it in SRAM first. If you find the data, you don't have to spend a lot of time reading it in RAM (synchronous reading). If there is no data in SRAM, read it in RAM. When RAM returns data, it not only returns the original data, but also "piggybacks" some seemingly unrelated data "before and after" the required data, and puts these data into SRAM.

The next time CPU reads data in SRAM, if the required data happens to be in SRAM, it can be "hit". It can be seen from the principle that the higher the hit rate, the higher the efficiency of CPU. While the hit rate is determined by the data returned by "piggyback", which data is returned by piggyback, the transaction of this site depends on the caching algorithm within CPU. Thus it can be seen that because the cache capacity is far less than the main memory capacity, and the cache algorithm can not be 100% accurate hit.

The role of caching in a mechanical hard disk:

The above is an example of CPU cache. But in computer systems, caching is not unique to CPU, because the contradiction between high-speed devices and low-speed devices is not just between CPU and memory. Now, if I want to write data from memory to the hard disk, because the hard disk is quite slow, it will take a long time to complete this task. So the user experience is that the computer is very slow. In fact, here CPU is not slow, memory is not slow, but the hard drive is too slow.

To solve the problem that the speed of the mechanical hard disk is too slow, a small capacity of memory, that is, the cache of the hard disk, is placed inside it, and the data is first written to the cache. Then at the operating system level, you will think that the data has been written, and the user's feeling is fast. The hard drive then writes itself from the cache to the disk, a process that does not require user intervention.

It is important to note, however, that not all hard disk caches are used to cache data, but there are other uses, so the larger the cache, the better the performance. And there is a caching algorithm problem. If the algorithm is not good, the hit rate will not be high, so a large cache is virtually non-existent.

The role of caching in SSD solid state drives:

Just now I introduced what cache is and the role it plays in mechanical hard disk and memory. In fact, the role of cache in SSD solid-state disk is not far different. The cache on SSD is generally composed of 1 or 2 DRAM particles, which acts as a data exchange buffer. Whether a SSD product has a cache design is often decided by the manufacturer according to the product positioning and use. generally, some entry-level products or low-speed products will consider the scheme without cache in the design, while some high-speed products are designed with cache because of the large data exchange capacity, in order to improve the reading and writing efficiency of the product.

SSD with caching is usually slightly more expensive than one without caching, although SSD can read small files faster with caching, but for SSD, the speed is too limited. In terms of reaction speed, the reaction speed of SSD is generally less than 0.2ms, which is no slower than cache. Therefore, the improvement of read speed with cache is almost negligible. Secondly, the lifetime of SSD is not affected by caching, which is determined by the number of writes to NAND FLASH. Secondly, the quality of the main control chip is an important factor that determines the performance and service life of SSD.

Summary of the article:

Through the author's introduction, I believe you have an in-depth understanding of the role of cache. in addition, we can see that caching memory, mechanical hard disk and SSD solid state disk play a different role. Cache exists to balance the speed difference between high-speed devices and low-speed devices, and its function is to keep low-speed devices from dragging the back of high-speed devices as far as possible.

The main function of caching is when the computer has data to put into the HDD, because the mechanical operation of the HDD is much slower than the computer, so put the cache on the HDD and store the data temporarily so that the computer can continue to do other things. It will not slow down the performance of the computer because of the slow action of the HDD.

On the other hand, the speed of SSD has been greatly improved, and it has been able to process data in real time, so the role of cache as a speed increase is not great. From this, we can draw a conclusion that judging the SSD speed according to the cache size is not scientific, and the speed of the solid state hard disk is mainly determined by the quality of the main control chip and flash memory particles.

At this point, I believe you have a deeper understanding of "what is the role of caching in SSD". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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