The environment in which a user interacts with a computer system. Each account has a unique name, which the user specifies when logging in. System data associated with an account controls what resources (files, programs, networks, etc.) the user can access and in what ways (e.g. whether files that are normally writeable are read-only for particular users) and to what extent (e.g. the total size of files a user creates may be limited). Where applicable, a record can be kept of the resources used for billing purposes.