ASPs may also be used to improve performance by isolating objects with similar performance characteristics, for example journal receivers, in their own pool. By default, all disk drives are assigned to pool 1. The concept of IBM i pools is similar to the Unix/Linux concept of volume groups; however, with IBM i it is typical for all disk drives to be assigned to a single ASP. Security Security in IBM i is defined in terms of authorities, which represents the permission to carry out a specific action on a specific object. Authorities can be granted to individual users (known as user profiles), groups (known as group profiles) or all users (public authorities). Related objects can be grouped together in an authorization list, making it possible to grant authorities on all objects in the list by granting authorities on the authorization list. User profiles have an associated user class which dictates the set of default authorities available to that user profile. There are five standard user classes which, in order of increasing privilege, are: Workstation User, System Operator, System Programmer, Security Administrator and Security Officer. IBM i ships with a default user profile for each user class, and the default Security Officer user profile, named QSECOFR, is the closest equivalent to the root user of a Unix-like operating system. IBM i can be set to use one of five levels of security, which control the extent to which the operating system's security features are enforced: Level 10 – Users can log in without a password, and have full access to the system. If a user logs in with an unknown username, a new user profile will be automatically created. Level 20 – Users must log in with a username and password of a known user profile, but will have almost full access to the system once logged in. Creation or modification of user profiles is restricted to user profiles which have been granted authorities for profile management. Limited access accounts can be created, which can be restricted to accessing certain objects, or running certain commands. Level 30 – Authorities are enforced, meaning that users cannot access objects unless they have an authority for the object. Level 40 – Access to certain system programs and MI instructions are restricted, and can only be used by operating system code. Level 50 – Includes changes needed for the system to achieve TCSEC C2 compliance,