There are many different kinds of memory used in embedded systems and new kinds are being developed all the time. However, we can split memory into two types; RAM and ROM
RAM stands for random access memory. The are two features of RAM which distinguish it from ROM:
RAM is read/write - data can be written to and read from RAM.
RAM is volatile - data is lost once the power to a RAM chip is lost.
Random access refers to the fact that data from any location in the memory chip is accessible at any time . However, RAM is actually a poor choice of name for this type of memory (its name is rooted in history) because it does not refer to its main features and it may lead you to believe other types of memory are not random access. A memory chip is of little use if it's not random access.
ROM stands for read only memory. As with RAM, it is random access but it differs from RAM in two ways:
ROM, as the name suggests, is read only. You cannot write to a ROM chip. A ROM chip must be programmed once and it cannot be (easily) changed.
ROM is non-volatile - when power is removed from the chip data is not lo
