When the CPU is working, it needs to read data from the external storage such as the hard disk, but because the "warehouse" of the hard disk is too large, and it is also "far away" from the CPU, the speed of transportation of "raw material" data is relatively slow, leading to a great reduction in the production efficiency of the CPU!
To solve this problem, people set up a "small warehouse" -- memory -- between the CPU and external storage.
Although the memory capacity is small, generally only tens of MB to several hundred MB, but the transfer speed is very fast, so that when the CPU needs data, can be stored in memory in advance, in order to solve the URGENT problem of the CPU.
Since memory is just a "transit warehouse," it cannot be used to store data for long periods of time.
