Stratus VOS

Key takeaways

Stratus VOS belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Stratus VOS to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Stratus VOS from memory before moving on to harder problems.

Reference excerpt

Stratus VOS (Virtual Operating System, now renamed as OpenVOS) 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-branded 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 many others. Numeric values in VOS are always big endian, regardless of the endianness of the underlying hardware platform. On little endian servers with x86 processors, the compilers do a byte swap before reading or writing values to memory to transform the data to or from the native little endian format.

Command Macro Language VOS has a fairly complete command macro language which can be used to create menu systems, automate tasks etc. VOS command macros accept arguments on the command-line or via a user interface "form". Arguments are defined at the beginning of the command macro in a "parameters" section. 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. It can be used to automate programs, capturing prompts and sending appropriate responses. This has led Stratus to limit the capabilities of the command macro language. The macro language lacks support for user-defined functions and does not easily support include files. The string handling is prone to errors, especially with embedded control characters. A Visual Studio Code Syntax Highlighting extension for VOS Command Macro can be found on the Visual Studio Marketplace.

Overview VOS was coded mainly in PL/I with a small amount of assembly language before it was migrated to ftServer series. As of 1991, the system was written in PL/I and C, with only 3% in assembly. 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.).

Distribution VOS is distributed only by Stratus Technologies. The distribution media is a 3.5 mm DAT tape for Continuum, and an SDLT tape for early V Series platforms. As of OpenVOS Release 17.0, Stratus offers support for distributing OpenVOS on a DVD or by downloading a release file. Software installations may be done by the Stratus Field Engineer or by the customer's system administrator.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Stratus VOS

Start with the simplest possible case. Write down what Stratus VOS claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Stratus VOS before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Stratus VOS ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Stratus VOS

In research: Stratus VOS appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Stratus VOS in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Stratus VOS is common in secondary-school and first-year university syllabi. It links to neighbouring topics Fault-tolerant computer systems, Multics-like, Proprietary operating systems, so understanding it makes those chapters shorter.
In everyday life: Look for Stratus VOS outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Stratus VOS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Stratus VOS means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Stratus VOS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Stratus VOS in simple terms?

Stratus VOS (Virtual Operating System, now renamed as OpenVOS) is a proprietary operating system running on Stratus Technologies fault-tolerant computer systems. VOS is available on Stratus's ftServer and Continuum platforms.

Why does Stratus VOS matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Stratus VOS?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Stratus VOS.