A Brief History of Digital Software

OpenVMS was designed from the outset to be a secure, multiuser system with full networking functionality. In fact, the VAX and VMS were designed concurrently at DEC by a hardware/software engineering team. The VAX is a CISC and included many instructions designed expressly to support VMS. The Alpha is a reduced instruction set computer (RISC). As OpenVMS evolved, new features such as symmetric multiprocessing (SMP) and clustering were added.

The conversion of the PDP-11 customer base to the VAX was accomplished by moving much of the PDP-11 operating system, RSX-11, to the VAX. RSX could be invoked as a DCL command, and the VAX hardware was designed to execute the PDP-11 instruction set. Even so, the new operating system, VAX/VMS, was part of the VAX-11 ^[3] release. Many OpenVMS concepts find their roots in RSX-11 (e.g., user identification code [UIC]; the name of the root directory, [000000]; and process privileges, to name a few). The DEC proprietary networking protocol, DECnet, is still compatible between a PDP-11/RSX-11 computer and an Alpha/OpenVMS computer.

Since 1993, OpenVMS has also been running on the 64-bit Alpha platform, a CPU pioneered by DEC and today, the primary OpenVMS host. About 50 Alpha models are supported, although many are no longer manufactured. Unlike the PDP-11-to-VAX transition, the operating system was unchanged when the Alpha was introduced. To expedite the switchover, a conversion routine was written so that any VAX executable could be converted to run on the Alpha. This was not a sales gimmick; it was a powerful tool used by DEC software engineers to transfer much of the VAX software to the Alpha.

Even while Compaq and HP were discussing their merger, plans were made to port OpenVMS to the Itanium. OpenVMS on the Itanium (IA-64) is due to be released in 2003 and 2004 in several stages. The Itanium computer is HP/Intel's entry into the 64-bit world.

The VAX is no longer made, but OpenVMS for that platform is still supported on several dozen models (depending on how they are counted) of the VAX computer.

For the record, VMS and OpenVMS are two names for the same operating system. Originally, the operating system was called VAX-11/VMS; it changed to VAX/VMS at Version 2.0. When the VMS operating system was ported to the Alpha platform, it was renamed OpenVMS, for both VAX and Alpha computers. In part, this name change signified the high degree of support for industry standards such as POSIX, which provides many features found in UNIX systems. What became confusing was that the OpenVMS name was introduced first for OpenVMS AXP V1.0, causing the widespread misunderstanding that OpenVMS was for Alpha AXP only, whereas "regular VMS" was for VAX. In fact, the official name of the VAX operating system was changed as of V5.5, although the name was not used until V6.0 was released. The proper names for OpenVMS on the two platforms are now "OpenVMS VAX" and "OpenVMS Alpha," the latter having superseded "OpenVMS AXP."

As new hardware—both peripherals and CPUs—become available, OpenVMS is upgraded and re-released. Software bugs and improvements are also included in the upgrades. In order to define which hardware is supported by which version of OpenVMS, the software product description (SPD) is updated with each upgrade. The SPD also includes a list and brief description of software products that are licensed by HP. Some third-party software is listed in the document.

The operating system is designed to perform well under any SPD-defined environment and can simultaneously support processes that exhibit extensive I/O demands, those that exhibit extensive CPU demands, real-time processes, and client/ server applications. OpenVMS automatically adapts itself to the number of CPUs, the amount of physical memory, and the number and type of disks attached to the computer.

There is a precise definition of the instruction set required for OpenVMS. The VAX supported "native" OpenVMS on most models. The instructions that were not built in were simulated in software; however, the base architecture of a given Alpha computer does not match this definition, so firmware (called PALcode) is loaded to emulate certain required OpenVMS instructions. System reference manual (SRM) console firmware controls the console before booting OpenVMS, and it is the boot program. It scans for the hardware configuration and stashes that information in memory for OpenVMS to access later. It initializes the CPU, cache control, memory management, and the basic I/O devices. Finally, it loads the primary boot program (the primary loads the secondary) from the system disk and transfers control to it.

A partial version of OpenVMS is available for the 86xx family. Called Charon-VAX, a product of Software Resources International (SRI), this effort is entirely independent of HP. It is available both commercially and for hobbyists. The URL is www.softresint.com/softresint/legal.htm. Charon-VAX is actually a MicroVAX emulator running as an application on Windows NT. The emulator is purchased from SRI, and OpenVMS is purchased from HP. Used VAX and Alpha computers can be purchased on eBay auction (search for VAX or DEC) and from any of several used computer companies.

^[3]The VAX-11 name was a marketing ploy to entice loyal PDP-11 customers—to assure them that this new machine was not a significant departure from the PDP-11.