[2] VOS customers use it to support high-volume transaction processing applications which require continuous availability.
[3] VOS was designed from its inception as a high-security transaction-processing environment tailored to fault-tolerant hardware.
[6] Like competing proprietary operating systems, VOS has seen its market share shrink steadily in the 1990s, and early 2000s.
[8] Each of these programming languages can make VOS system calls (e.g. s$seq_read to read a record from a file), and has extensions to support varying-length strings in PL/I style.
Each additional release of VOS has added more POSIX.1 capabilities, to the point where many user-mode open-source packages can now be successfully built.
Stratus offers supported ports of Samba, OpenSSL, OpenSSH, GNU Privacy Guard, OpenLDAP, Berkeley DB, MySQL Community Server, Apache, IBM WebSphere MQ, and the community edition of Java.
VOS has a fairly complete command macro language which can be used to create menu systems, automate tasks etc.
The language supports a range of statements, including if/then/else, Boolean operations, "while" loops, "goto" and excellent error reporting.
The command macro language can be executed in interactive and non-interactive (batch or started process) modes.
VOS was coded mainly in PL/I with a small amount of assembly language before it was migrated to ftServer series.
The former is used by VOS to determine the process's access rights to external devices, and items with the file system.
Command macros and programs can be invoked with an argument to display a form listing all the available parameters, which the user can navigate using the "tab" key.
These boards are actively monitored by the operating system which can correct any minor inconsistencies (such as bad disk-writes or reads).
Stratus Customer Service will then dial into the system using RSN to investigate the problem and dispatch replacement parts.
The operating system is designed to avoid crashes due to a simplexed hardware failure.
In modern versions of VOS, paging files can be created dynamically by the SysAdmin (but not removed without a reboot).
These paging files can in theory consist of more than one extent (which is viewed by the kernel as a mini-paging partition) which may or may not be contiguous.
Admin should create the largest possible extent for the paging files as early as possible after the system has been booted.
Virtually every system call in the native API has a parameter that determines what computer the operation affects.
Historically, StrataLINK was a proprietary 10Mb CSMA/CD ring network which allowed high performance (for the time) with very low memory overhead and CPU utilization.
This was never developed beyond 10Mb and was dropped in favor of using TCP/IP because Ethernet became the dominant networking standard and because memory and CPU processing got cheaper.