TwoOStwo
Encyclopedia
twoOStwo was a commercial software product developed by Parallels Software Studio
(prior to its acquisition by SWsoft
). The workstation software consisted of a virtual machine
suite for Intel x86-compatible computers which allowed the creation and execution of multiple x86 virtual computers simultaneously. Each virtual machine instance could execute its own guest operating system
including Windows
, Linux
, OS/2 and BSD variants.
and operating system instance that executes the twoOStwo process is referred to as the host machine. Instances of operating systems running inside a virtual machine are referred to as guest virtual machines. Like an emulator
, twoOStwo provides a completely virtualized set of hardware to the guest operating system; for example, irrespective of make and model of the physical network adapter, the guest machine will see an Novell
/Eagle
NE2000 or Realtek
RTL8029(AS) network adapter. twoOStwo virtualizes all devices within the virtual environment, including the video adapter, network adapter, and hard disk
adapters. It also provides pass-through drivers for serial and parallel devices.
Because all guest virtual machines use the same hardware drivers irrespective of the actual hardware on the host computer, virtual machine instances are highly portable between computers. For example, a running virtual machine can be stopped, copied to another physical computer, and started.
emulate the microprocessor, executing each guest CPU
instruction by calling a software subroutine on the host machine that simulates the function of that CPU instruction. This level of abstraction allows the guest machine to run on host machines with a different type of microprocessor, but is also very slow.
A more efficient approach consists in software debugger
technique. Some parts of the code are executed natively on the real processor; on 'bad' instructions, there are software interrupts that break execution of the guest operating system code and that particular instruction is emulated.
twoOStwo, as well as VMware Workstation
, Virtual PC for Windows
and QEMU
with the kqemu add-on, take an even more optimized approach and run code directly when this is possible. This is the case for user mode and virtual 8086 mode
code on x86.
The drawback is that the guest OS has to be compatible with the host CPU. So unlike an emulator, one cannot use twoOStwo to run Mac
/PowerPC
software on an Intel x86 processor. Another drawback is that it is not normally possible to efficiently nest virtual machines. Finally, although twoOStwo virtual machines run in user mode, twoOStwo itself requires installing various device drivers in the host operating system.
readers and hard disk drives, twoOStwo also provides the ability to simulate some hardware. For example, an ISO image
can be mounted as a CDROM and .hdd files can be mounted as hard disks.
Parallels, Inc.
Parallels, Inc. is a privately held virtualization technology company with offices in the USA, Germany, UK, France, Japan, China, Russia and Ukraine. Parallels' US offices are in Renton, WA.The company has more than 700 employees as of 2010....
(prior to its acquisition by SWsoft
SWsoft
SWsoft was a privately held server automation and virtualization software company and the parent company of Parallels, Inc. SWsoft developed software for running data centers, particularly for web-hosting services companies, application service providers, and managed service providers...
). The workstation software consisted of a virtual machine
Virtual machine
A virtual machine is a "completely isolated guest operating system installation within a normal host operating system". Modern virtual machines are implemented with either software emulation or hardware virtualization or both together.-VM Definitions:A virtual machine is a software...
suite for Intel x86-compatible computers which allowed the creation and execution of multiple x86 virtual computers simultaneously. Each virtual machine instance could execute its own guest operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
including Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
, Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, OS/2 and BSD variants.
Description
The computerComputer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
and operating system instance that executes the twoOStwo process is referred to as the host machine. Instances of operating systems running inside a virtual machine are referred to as guest virtual machines. Like an emulator
Emulator
In computing, an emulator is hardware or software or both that duplicates the functions of a first computer system in a different second computer system, so that the behavior of the second system closely resembles the behavior of the first system...
, twoOStwo provides a completely virtualized set of hardware to the guest operating system; for example, irrespective of make and model of the physical network adapter, the guest machine will see an Novell
Novell
Novell, Inc. is a multinational software and services company. It is a wholly owned subsidiary of The Attachmate Group. It specializes in network operating systems, such as Novell NetWare; systems management solutions, such as Novell ZENworks; and collaboration solutions, such as Novell Groupwise...
/Eagle
Eagle
Eagles are members of the bird family Accipitridae, and belong to several genera which are not necessarily closely related to each other. Most of the more than 60 species occur in Eurasia and Africa. Outside this area, just two species can be found in the United States and Canada, nine more in...
NE2000 or Realtek
Realtek
Realtek Semiconductor Corp. , a fabless IC design house situated in the Hsinchu Science Park, Hsinchu, Taiwan, was founded in October 1987, and subsequently approved as a listed company on the Taiwan Stock Exchange in 1998...
RTL8029(AS) network adapter. twoOStwo virtualizes all devices within the virtual environment, including the video adapter, network adapter, and hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
adapters. It also provides pass-through drivers for serial and parallel devices.
Because all guest virtual machines use the same hardware drivers irrespective of the actual hardware on the host computer, virtual machine instances are highly portable between computers. For example, a running virtual machine can be stopped, copied to another physical computer, and started.
Implementation
Conventional emulators like BochsBochs
Bochs is a portable x86 and x86-64 IBM PC compatible emulator and debugger mostly written in C++ and distributed as free software under GNU Lesser General Public License...
emulate the microprocessor, executing each guest CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
instruction by calling a software subroutine on the host machine that simulates the function of that CPU instruction. This level of abstraction allows the guest machine to run on host machines with a different type of microprocessor, but is also very slow.
A more efficient approach consists in software debugger
Debugger
A debugger or debugging tool is a computer program that is used to test and debug other programs . The code to be examined might alternatively be running on an instruction set simulator , a technique that allows great power in its ability to halt when specific conditions are encountered but which...
technique. Some parts of the code are executed natively on the real processor; on 'bad' instructions, there are software interrupts that break execution of the guest operating system code and that particular instruction is emulated.
twoOStwo, as well as VMware Workstation
VMware Workstation
VMware Workstation is a virtual machine software suite for x86 and x86-64 computers from VMware, a division of EMC Corporation, which allows users to set up multiple x86 and x86-64 virtual machines and use one or more of these virtual machines simultaneously with the hosting operating system...
, Virtual PC for Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
and QEMU
QEMU
QEMU is a processor emulator that relies on dynamic binary translation to achieve a reasonable speed while being easy to port on new host CPU architectures....
with the kqemu add-on, take an even more optimized approach and run code directly when this is possible. This is the case for user mode and virtual 8086 mode
Virtual 8086 mode
In the 80386 microprocessor and later, virtual 8086 mode allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running a protected mode operating system.VM86 mode uses a segmentation scheme identical to that of real mode In...
code on x86.
The drawback is that the guest OS has to be compatible with the host CPU. So unlike an emulator, one cannot use twoOStwo to run Mac
Mac OS
Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...
/PowerPC
PowerPC
PowerPC is a RISC architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM...
software on an Intel x86 processor. Another drawback is that it is not normally possible to efficiently nest virtual machines. Finally, although twoOStwo virtual machines run in user mode, twoOStwo itself requires installing various device drivers in the host operating system.
Features
Besides bridging to network adapters, CD-ROMCD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....
readers and hard disk drives, twoOStwo also provides the ability to simulate some hardware. For example, an ISO image
ISO image
An ISO image is an archive file of an optical disc, composed of the data contents of every written sector of an optical disc, including the optical disc file system...
can be mounted as a CDROM and .hdd files can be mounted as hard disks.
See also
- Parallels WorkstationParallels WorkstationParallels Workstation is the first commercial software product released by Parallels, Inc., a developer of desktop and server virtualization software...
- SVISTASVISTASVISTA is a former commercial virtual machine software product marketed by Serenity Systems International. Windows, OS/2, Linux and FreeBSD hosted versions were available.This product is no longer available nor supported....
- VMwareVMwareVMware, Inc. is a company providing virtualization software founded in 1998 and based in Palo Alto, California, USA. The company was acquired by EMC Corporation in 2004, and operates as a separate software subsidiary ....
- User Mode Linux
- Xen
- Comparison of platform virtual machines