These days, almost all memory comes in the form of memory modules and is installed in sockets located on the system motherboard. Memory sockets are easy to spot because they are normally the only sockets of their size on the board. Examples of where memory can be installed. A memory bank is a group of sockets or modules that make up one logical unit. So, memory sockets that are physically arranged in rows may be part of one bank or divided into different banks.
Most computer systems have two or more memory banks - usually called bank A, bank B, and so on.
And each system has rules or conventions on how memory banks should be filled. For example, some computer systems require all the sockets in one bank to be filled with the same capacity module. Some computers require the first bank to house the highest capacity modules. If the configuration rules aren't followed, the computer may not start up or it may not recognize all the memory in the system. You can usually find the memory configuration rules specific to your computer system in the computer's system manual.