Overview
VOS was coded mainly in PL/I with a small amount of assembly language before it was migrated to ftServer series but now it is coded in POSIX compliant C & C++, assembly language and legacy PL/I. Its overall structure has much in common with Multics, and many of the system's sophisticated features can be traced back to Multics to varying degrees. The system exposes a number of fundamental abstractions to the software designer or programmer, most notable being
- Processes
- Devices
- Hard Disks
- Various IPC mechanisms
- Tasks
A process is the scheduled entity in VOS and each process has a set of attributes that govern how it is manipulated by the system. For example processes have a user name and process name. The former is used by VOS to determine the process's access rights to external devices and items with the file system. Of fundamental significance is a process's privileged flag, which is a binary attribute. Privileged processes may perform privileged operations. This mechanism is used to restrict certain potentially powerful operations that can have system wide consequences (e.g. shutting down the system, dismounting a hard disk etc.).
Read more about this topic: Stratus VOS