A PLC memory unit stores all data such as user programs, I/O memory data, comment information, and setting information of a CPU module or an advanced function module in a PLC. The memory areas include user program areas for storing designed user programs, I/O memory areas accessible by instruction operands, and parameter areas for handling initial setting information. Some include a non-volatile memory and some can transfer programs between controllers. There are multiple types of memory including additional memory boards and memory cartridges. When selecting a product, check the memory capacity and representative standards in addition to the type.