Stratus VOS (Virtual Operating System) is a proprietary operating system running on Stratus Technologies fault-tolerant computer systems. VOS is available on Stratus's ftServer and Continuum platforms. VOS customers use it to support high-volume transaction processing applications which require continuous availability. VOS is notable for being one of the few operating systems which run on fully lockstepped hardware. During the 1980s, an IBM version of Stratus VOS existed and was called the System/88 Operating System. History VOS was designed from its inception as a high-security transaction-processing environment tailored to fault-tolerant hardware. It incorporates much of the design experience that came out of the MIT/Bell-Laboratories/General-Electric (later Honeywell) Multics project. In 1984, Stratus added a UNIX System V implementation called Unix System Facilities (USF) to VOS, integrating Unix and VOS at the kernel level. In recent years, Stratus has added POSIX-compliance, and many open source packages can run on VOS. Like competing proprietary operating systems, VOS has seen its market share shrink steadily in the 1990s and early 2000s. Development Programming for VOS VOS provides compilers for PL/I, COBOL, Pascal, FORTRAN, C (with the VOS C and GCC compilers), and C++ (also GCC). 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. Developers typically code in their favourite VOS text editor, or offline, before compiling on the system; there are no VOS IDE applications. In its history, Stratus has offered hardware platforms based on the Motorola 68000 microprocessor family ("FT" and "XA" series), the Intel i860 microprocessor family ("XA/R" series), the HP PA-RISC processor family ("Continuum" series), and the Intel Xeon x86 processor family ("V Series"). All versions of VOS offer compilers targeted at the native instruction set, and some versions of VOS offer cross-compilers. Stratus added support for the POSIX API in VOS Release 14.3 (on Continuum), and added support for the GNU C/C++ compiler, GNU gdb debugger, and many POSIX commands in VOS Release 14.4. 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. For this reason, beginning with Release 17.0, Stratus renamed VOS to OpenVOS. 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. Numeric values in VOS