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Bochs x86 IA-32 Emulator 2.1 Released
Asmodeus writes "Just noticed that the 2.1 release of the Bochs IA-32 emulator is out at the Bochs home page
For those not in the know, Bochs is an open source implementation of the x86 instruction set(s) and a virtual PC (al la VMWare) which is capable of booting FreeDOS and Linux under the host control of another OS."
Bochs emulates the IA-32 instruction set and enables you to run IA-32 software on any sort of hardware that you can compile Bochs on. (eg. I once ran it on a MicroVAX at an incredibly slow speed)
VMWare requires IA-32 hardware. Most of the instructions are executed natively and only some of the priviledged operations are emulated so that whatever is run under VMWare can work as if it has full control over the CPU while in fact being an un-priviledged task.
Bochs isn't just capable of running DOS clones:
Operating Systems inside the emulation including Linux, Windows(R) 95, DOS, and Windows(R) NT 4
It can also run Windows 2000 - and probably XP as well if product activation works.
But if it's retro DOS games you're after check out dosbox which runs pretty fast and runs on many platforms.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
This post has no point. It just provides some general (hopefully interesting) background info.
As many people pointed out, Bochs is an x86 emulator, rather than a virtualization system like VMWare. Emulation means that you have a representation of an x86 machine in memory, look at each instruction, and change the representation appropriately. Virtualization means the code runs on the actual CPU natively, and uses 386 ninja powers to intercept all I/O calls and reroute them to the base OS.
As a result, Bochs will run on any platform. VMWare will only run on x86. Bochs is slow enough to be useless for most common uses (a bit over a 100x hit in speed). VMWare has almost no hit in speed.
However, the free software community did have a project that attempted to reimplement VMWare. That project was called Plex86 (http://plex86.sourceforge.net/). For reasons that I do not know, Plex86 recently reinvented itself not to do full hardware virtualization -- rather, it does not implement the I/O layer, and instead provides special drivers for Linux to talk to its I/O layer. As a result, it can only run Linux (although it claims to run it reasonably well). They may implement drivers for other platforms, but I would be fairly sceptical of any real Windows support anytime soon. That seems a lot less useful now...
The Plex86 project, however, claims the possibility of using their virtualization technology in conjunction with Bochs to make a useable system: "There is the potential to use plex86 as an accelerator for bochs, as was demonstrated some time ago." (source: Plex86 FAQ). Likewise, it seems that if Bochs was more intelligently implemented, they could use just-in-time recompliation, a la Java or Transmeta, since they are effectively treating the x86 ISA as bytecode. That would be in the very, very distant future, but if either of these is implemented, the Bochs project is not as hopeless for end-user use as it may at first seem... Either or both of these technologies ought to give reasonable performance.
One problem is that VMWare is creating a patent minefield in front of Plex86 and Bochs. I am not familiar with all of the patents, but from what I've heard, they've got a pretty wide field of IP cut out. I'm not sure how hard they'll exploit it, since the people working there seem like nice guys, and understand the whole open/Linux/GNU/free/etc. thing. On the other hand, so did Caldera a few years back, and VMWare is definitely getting those patents for a reason....
One final point -- properly used, emulators like Bochs can provide amazingly powerful debugging tools. You can run a full x86 machine (admittedly at very slow speeds), but grab snapshots of the system memory at different points. You can then roll back, use a capture of all inputs to roll forward, etc.
Plex86 (and Xen, VMware, and Connectix, and Ensim, and others) are the things people should look at if they want fast virtualization of x86. The trouble all these technologies run into is that IO has to go through the "host" OS (the one actually running on the metal) - often popping into userspace to do it (read: context & ring switches --> slow!). This is necessary in order to allow multiple virtualized OS's to share the IO devices. This causes stuff that is IO intensive (games, compilers, databases, etc.) take a fairly serious performance hit. Interestingly enough, Intel is working on building this sort of capability in the chips directly - check out Vanderpool for instance. I don't know if AMD is doing anything similar, anybody heard anything?
I got bochs v2.1 to run Windows XP without any problems. The trick is to configure bochs with --enable-cpu-level=5 --disable-sse.
Here are some screenshots and a howto