Shulou(Shulou.com)06/02 Report--

Cache (Cache, referred to as cache), the original meaning refers to the access speed of a RAM faster than the general random access memory (RAM), usually it does not use DRAM technology like the system main memory, but uses expensive but fast SRAM technology. Cache is a memory located between CPU and DRAM, which is usually composed of SRAM with small scale and fast access speed.

At present, the concept of cache has been expanded, there is not only Cache between CPU and main memory, but also Cache (disk cache) between memory and hard disk, and even Cache ── between hard disk and network is called Internet temporary folder or network content cache and so on. Any structure that is located between two kinds of hardware with large difference in speed and is used to coordinate the difference in data transmission speed between the two can be called Cache.

working principle

1. Pre-read: when the hard disk is controlled by the CPU instruction to start reading data, the control chip on the hard disk will control the magnetic head to read the data in the next cluster or clusters being read into the cache. When it is necessary to read the data in the next cluster or clusters, the hard disk does not need to read the data again, just transfer the data in the cache to memory. Because the cache rate is much higher than the head read and write rate, it can achieve the purpose of significantly improving performance.

2. Write: when the hard disk receives the instruction to write data, it will not immediately write the data to the disk, but will temporarily store the data in the cache, and then send a "data has been written" signal to the system. At this time, the system will think that the data has been written and continue to perform the following work, while the hard disk will write the data in the cache to the disk when it is idle (when there is no reading or writing).

3, temporary storage: some data will often need to be accessed, such as the cache inside the hard disk (one of the registers) will store some data that is read more frequently in the cache, and can be directly transferred from the cache when it is read again.

Function meaning

Temporarily store the data processing results and provide the next access to use. In many cases, data processing or data acquisition may be very time-consuming, when the amount of requests for this data is very large, frequent data processing will consume a lot of resources. The function of cache is to store these hard-won data. When this data is requested again, it is directly obtained from the cache and the data processing process is omitted, so as to reduce the consumption of resources and improve the response speed.

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