The inforamtion in memory could be program instructions, numbers for arithmetic, codes representing text characters, a part of a picture, or other kinds of data. Each byte has an address that identifies it and helps the CPU keep track of where things are stored. A typical personal computer has from 16 to 64 megabytes of memory. The CPU can only see into and access memory. Memory addresses make up the CPU's entire world, so any program that needs to be executed or data that needs to be modified must make its way into memory.
Memory is composed of storage cells called bytes.
For example, inforamtion to be displayed on the monitor screen is written into a special range of memory addresses that is continually scanned by the video subsystem.