An address is a name (in the general sense of an identifier) for either:
- a unit of storage, either main memory or secondary storage; or
- something in a communication network.
For the former, the hardware reacts to references to a given address by using the unit of storage at that address.
For main memory, an address uniquely names the fundamental unit of memory - a byte in most contemporary machines (following the example of the IBM System/360, or a word (typical, on older machines). Main memory cells are arranged in an array, and the address is the index into that array.
Addresses for secondary storage can be more complicated; for disks, disk addresses (particularly on older disks) include separate cylinder, surface and sector fields. For magnetic tape drives, records or blocks are usually numbered sequentially.
Networking also has addresses (which usually include some information about where in the network the named thing is, they do not just uniquely identify the entity). In some protocol suites, interfaces are given addresses, in others, it is hosts which have them.