Protection: The protection mechanisms of VMS described in terms of the access matrix model

Most system resources, notably disk files, are protected by UIC.

Access Control Lists appeared in VMS 4.0

Note that this is a very limited form of access control list. While an owner can list access for users in the various categories, there is no way to grant access to a specific user in a category without granting the same access to all users in that category. Therefore, beginning with version 4.0, VMS has also included the option of adding a full-blown access control list to an object, in addition to the protection codes for the four categories of user.