Editing Stratus VOS (section)

==Overview==
VOS was coded mainly in [[PL/I]] with a small amount of [[assembly language]] before it was migrated to ftServer series.{{Citation needed|date=January 2016}} As of 1991, the system was written in PL/I and C, with only 3% in assembly.<ref>{{cite news |first=Maryfran |last=Johnson |title=Stratus compiler spells migration boost |newspaper=Computerworld |date=1 April 1991 |pages=25, 32 |url=https://books.google.com/books?id=sXM8jj29gfIC&pg=PA25}}</ref>

Its overall structure has much in common with Multics, and many of the system's 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.).