What does the address unit in the single chip microcomputer mean?

Ram8 bits in the single chip microcomputer are a unit, that is, every 8-bit binary number is a storage unit. There are 256 such storage units in RAM. The first 128 units are general storage units, and the last 128 units are special function registers. In fact, there are only 21 special function registers, and other blanks are not defined. For example, you should know the medicine cabinet used in traditional Chinese medicine, When filling the medicine, draw out a box by box, just like that. Such a drawer is a unit, and a small box inside is a bit of the storage unit. What medicine is there in the small box written outside the drawer, so that you can find it, that is, the address of this unit, which is called the byte address in the book.