Instead, the user's own device must show this message in a way so that the user can recognise it as a message from her own device. The Preference Services define what choices a user has and what default values are given. In addition, the preference block keeps stores the actually installed configuration, i.e., all information specific to a particular installation like the target system, the memory size, the screen type or any other hardware devices currently supported. Access Control Services . Access control ensures that potentially dangerous, compromising or undesirable operations cannot be performed by unauthorised users or without the user's explicit consent.
Access control is capability based.
Such a capability must be verified each time the corresponding method is called. The Access Control Block provides the necessary services to manage such capabilities based on roles. By the way, we assume that they only try to access each other nicely by their services, i.e., that the operating system does not allow them to tamper with each other's code or memory. The roles are currently unlocked after appropriate user authoization. In addition, the actual implementation also contains a utility block with various utility services for, e.g., converting objects into streams of bytes, and for logging and debugging.