DOS extender that adds Unix like multi-user capabilities. Version 3.0 will be DPMI compliant and will use a new portable microkernel named 'BABy'.

Discontinued microkernel operating system that was developed by faculty and students in the distributed systems group at Stanford University.

Stanford University, USA

Operating system focused on speed for projects like real-time video serving, etc.

V2 Lab, Netherlands

Project to build out a Lisp-based OS based on a persistent object store and has quite a few other interesting principles.

Australia

Virtual-machine monitor. TCSEC A1-class, VMM for VAX computers.

DEC, USA

Standard operating system for DEC VAX. Based on RSX-11.

USA

Realtime object-oriented OS for the MicroVAX.

USA

Real-time operating system.

Green Hills Software, USA

Discontinued version of the Unix operating system for low-end computers.

VenturCom, USA

Like the original Venix/86, it included a C compiler, a Basic interpreter and added a Fortran 77 compiler as an option.

Based on System V.

Last version. Based on UNIX System V Release 4.2 (UnixWare).

Experimental OS for a modified Interdata minicomputer, based on matching the computer architecture to the operating system.

Barbara Liskov, USA

Platform release of EOS that is supported on Amazon Web Service (AWS), Microsoft Azure and other public clouds.

Arista, USA

MS-DOS compatible system for 68000.

Motorola, USA

Operating system built of reusable, replacable components that can be organized by the end-user, even code running in kernel mode.

Harvard University, USA

DEC's proprietary operating system originally produced for its VAX minicomputer. Renamed "OpenVMS" around version 5.5.

DEC, USA

First GUI for early PC machines. Not commercially successful.

VisiCorp, USA

Visual Operating System. The operating system is licensed under the GNU GPL.

Andy McLaughlin, Canada

Virtual Machine Facility/370. Virtual memory operating system. To assist customers in migration from OS/360 to OS/VS.

IBM, USA

Virtual Machine/Basic Extended Product. Functional ehancement to VM/370.

IBM, USA

Virtual Machine / Extended System Architecture, added 31-bit addressing to VM series.

IBM, USA

Version of VM/370 for the PC/370.

IBM, USA

Virtual Machine/Extended Product. Functional ehancement to VM/370.

IBM, USA

Virtual Machine/System Product.

IBM, USA

VM/eXtended Architecture for System/370 with extended virtual memory.

IBM, USA

Virtual Machine/Extended Architecture Migration Assistance. Tool to assist in migration from MVS/370 to MVS/XA.

IBM, USA

Virtual Machine/Extended Architecture System Facility. Allow the machine to provide execution in the virtual-machine environment of most of the instructions (including many privileged instructions) and most of the facilities (such as dynamic address translation) of both the System/370 and the 370-XA architectures.

IBM, USA

Virtual Machine/Extended Architecture System Product.

IBM, USA

Hypervisor from Fujitsu (formerly Siemens Nixdorf Informationssysteme) designed specifically for use with the BS2000 operating system. It is an EBCDIC-based operating system.

Siemens, Germany

Targeted at the mid-range systems such as the 2960.

Never actually launched.

Virtual Machine Environment. Mainframe operating system. Implementation language S3 (ALGOL 68).

ICL, UK

Targeted at large processors such as the 2970/2980.

Merger of VME/B and VME/K, it was in reality the VME/B base with a few selected features from VME/K grafted on.

New Version of this Multiuser DOS, originally introduced in 1984, The design of VMiX has changed to allow it to migrate from IA32 architectures to the newer AMD64 and IA64 environments.

SysDev, USA

Virtual Memory Operating System. Timesharing OS for the RCA Spectra 70.

RCA, USA

Originally by DEC and HP now by VMS Software Inc. for the VAX mini-computer range, Alpha and Intel Itanium i2 and i4; later renamed OpenVMS.

DEC, USA

Last version. Succeeded by OpenVMS 6.0.

Omnitasking realtime executive for Varian minicomputers.

USA

Virtual machine OS running on the Michigan Terminal System.

USA

Operating System for Harris 600, 700, 800 computers.

USA

Virtual Operating System. Proprietary operating system running on Stratus Technologies fault-tolerant computer systems. With strong influence from Multics.

Stratus Technologies, USA

Operating system for HITAC L series distributed processing computers.

Hitachi, Japan

Operating system for lower models in Hitachi's HITAC M series of general-purpose computers, was the second OS in the M series following VOS2.

Hitachi, Japan

Operating system for HITAC L series distributed processing computers.

General-purpose medium OS suitable for departmental distributed processing.

Upgraded operating system over VOS1/ES2.

Was the first OS for the HITAC M series, which was a series of Hitachi's general-purpose computers.

Hitachi, Japan

Virtual-storage Operating System 3. For its IBM-compatible mainframes, based on IBM's MVS.

Hitachi, Japan

Operating system for HITAC M series computers.

Multiple virtual storage system that provided an independent 16-MB virtual storage to each job.

Operating system for HITAC M computers.

Upgraded operating system over VOS3/AS, which supported the MP5800, which was the world’s fastest single-processor machine in 1995, and its smaller sister models, including the MP5500.

Small/medium OS for M-620, M-630 and M-640.

Hitachi, Japan

Replaced the department computer operating system VOSK, was developed as a mid-range total management server with the features of a database server, a computing server, and a management server.

Hitachi, Japan

Virtual Processing System/Virtual Machine. Was an operating system that ran on IBM System/370 – IBM 3090 computers at Boston University in general use from 1977 to around 1990, and in limited use until at least 1993.

IBM, USA

Versatile Real-Time Executive. Real-time operating system suitable for both traditional board-based embedded systems and SoC architectures. It has been superseded by the Nucleus RTOS.

Mentor Graphics, USA

Virtual Resource eXecutive. Proprietary operating system on the NCR Criterion series, and later the V-8000 series of mainframe computers manufactured by NCR during the 1970s and 1980s. It replaced the B3 Operating System.

NCR, USA

Operating system for Wang VS series systems.

Wang Laboratories, USA

Successor to RCA TSOS. Discontinued computer operating system available for the UNIVAC Series 90 mainframes during the late 1960s through 1980s.

Sperry UNIVAC, USA

IBM Virtual Storage OS. See OS/VS1.

IBM, USA

IBM Virtual Storage OS. See OS/VS2.

IBM, USA

DOS/VSE extended virtual memory support to 32-bit addresses (Extended System Architecture).

IBM, USA

Program product replacing DOS/VSE and VSE/AF.

IBM, USA

Virtual Storage Operating System. Operating system for the Cyber 205 pipelined processor.

USA

Valencia's Simple Tasker. Was an operating system with a microkernel architecture, with all device drivers and file systems residing in userspace mode.

Virtual Technology’s Operating System. The second TRS‑80 Model I operating system.

Randy Cook, Virtual Technology, USA

Operating System for Harris computers.

USA

Small footprint, scalable, high-performance RTOS for embedded microprocessor based systems.

Wind River Systems, USA

Operating system on cartridge.

V-Marc, USA