Main Memory Organization




Main Memory Organization

Main memory of a computer system consists of several small storage areas called locations or cells. Each of these locations can store a fixed number of bits called word length of the memory. Hence, as a given memory is divided into N words, where N is generally some power of 2. Each word location has built-in and unique number assigned to it. This number is called address of the location and is used to identify the location. Each location can hold either a data from item or an instruction and its address remains the same, regardless of its contents. The first address normally starts at 0 and the highest address equals the number of words that can be stored in the memory minus 1. For example, if a memory has 1024 locations, its address ranges between 0 and 1023. Hence, at address 0 we find a word, at address 1 a second word, at address 2 a third word, and so on, up to the final word at the last address (1023).

There is an important difference between address of a memory location and its content. A memory is like a large abineta having as many drawers as there are addresses in memory. Each drawer contains a word and address of each is written on the drawer. If we write or store a word,say 10101010 at address 125, it is like placxing the word 10101010. We do not remove in it. Hence, entering data into a storage location is destructive of previous content but retrieving data from a location is non-destructive. The act of entering data into a storage location is called memory write operation, and the act of retrieving data from a storage location is called memory read operation. Hence, read is a non-destructive operation, and write is a destructive operation.