What is the principle of cache mechanism?

The principle of the cache mechanism is described as "locality principle", "cache structure", "cache hit and cache miss", "replacement strategy" and "write strategy" five steps: 1. Locality Principle, using the locality principle of program access to data; 2. Cache structure, cache is usually composed of multi-level cache, each level has different capacity and speed characteristics; 3. Cache hit and cache miss, when the CPU needs When reading or writing data, the cache level closest to it will first be checked; 4. Replacement strategy, if a cache miss occurs, the data is loaded from main memory to the cache, etc.

Operating system for this tutorial: Windows 10 system, Dell G3 computer.

The cache (Cache) mechanism is a storage hierarchy located between the CPU and main memory to improve the speed and efficiency of data access. It reduces the frequency of reading data from main memory by keeping a copy of some data closer to the CPU.

The principle of the cache mechanism can be simply described as the following steps:

1. Locality Principle: The cache uses the program to access data the principle of locality. During the execution of a program, there is usually temporal locality and spatial locality. Temporal locality means that the data being accessed is likely to be accessed again in the near future; spatial locality means that data near the data being accessed is likely to be accessed again in the near future.

2. Cache structure: Cache usually consists of multiple levels of cache, each level has different capacity and speed characteristics. Generally speaking, the closer the cache is to the CPU, the smaller the capacity and the faster it is. The most common ones are L1 cache, L2 cache and L3 cache.

3. Cache Hit vs. Cache Miss: When the CPU needs to read or write data, it first checks the cache level closest to it (such as the L1 cache). If the required data is already in the cache, a cache hit occurs and the CPU can read or write the data directly from the cache without accessing main memory. If the required data is not in the cache, a cache miss occurs and the CPU must load or write back the data from main memory.

4. Replacement strategy: When a cache miss occurs, data needs to be loaded from main memory into the cache. Due to the limited cache capacity, when the cache is full, a replacement data block needs to be selected. Common replacement strategies include least recently used (LRU), first-in-first-out (FIFO), and random replacement.

5. Write strategy: When the CPU writes data, it can use different write strategies. Common write strategies include Write Back and Write Through. The write-back strategy temporarily stores data modifications in the cache, and will only be written back to the main memory when the data is replaced from the cache or read by the CPU; the write-through strategy requires that the main memory be updated immediately for each write operation.

Through these principles and technologies, the cache mechanism can significantly improve the performance of the computer system, reduce the number of accesses to main memory, and speed up data access.

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