What is the difference between Buffer and Cache?

1 , buffer (buffer)

It is designed to increase the speed of data exchange between memory and hard disk (or other I/O devices).

2, cache (cache)

From the perspective of the CPU, it is designed to improve the data exchange speed between the CPU and the memory, such as the first-level cache, the second-level cache, and the third-level cache.

The instructions and read data used by the cpu to execute the program are all memory-oriented, that is, obtained from memory. Due to the slow memory read and write speed, in order to improve the speed of data exchange between cpu and memory, a cache is added between cpu and memory, which is faster than memory, but the cost is high, and because there is too much integration in the cpu. Circuit, so the general cache is relatively small, in order to further improve the speed, and added a secondary cache, or even a three-level cache, it is designed according to the local principle of the program, that is, the instructions executed by the cpu and the accessed data are often concentrated. A certain block, so after putting this piece of content into the cache, the cpu does not need to access the memory, which improves the access speed. Of course, if there is no content required by the CPU in the cache, you still need to access the memory.

From the perspective of memory read and disk read, cache can be understood as the operating system for more read efficiency, more memory to cache data that may be accessed again.

Buffers are designed according to the read and write of the disk, and the distributed write operations are concentrated to reduce disk fragmentation and repeated seeks of the hard disk, thereby improving system performance. Linux has a daemon that periodically clears the buffered content (that is, writes to disk), or you can manually clear the buffer by using the sync command.

Simply put, the buffer is about to be written to disk, and the cache is read from the disk. Buffers are allocated by various processes and are used in areas such as input queues. A simple example is that a process requires multiple fields to be read in. Before all fields are read in, the process saves the previously read fields in the buffer.

The cache is often used on disk I/O requests. If there are multiple processes accessing a file, the file is cached for next access, which improves system performance.

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