2006-06-28
A newly-released virtual machine app called Parallels Desktop for the Mac (they have it for other platforms, too) allows you to create as many virtual PCs as you want, each of which can run various versions of Windows, Linux, FreeBSD, and a few other systems. Parallels Desktop can take advantage of hardware support for virtualization that's present in newer Intel chips, such as the one in the iMac.
The release of Parallels Desktop for the Mac follows by a few months Apple's release of a beta of Boot Camp, which takes a completely different approach. Boot Camp doesn't virtualize anything; it simply sets up the iMac for dual-booting and supplies drivers that Windows XP needs to fully exploit the iMac hardware.
Now that I've had a chance to play around a bit with both, here are some things I've learned along with some of my own observations:
- With Parallels, the CPU isn't emulated--it's virtualized. So, most machine instructions are executed as native instructions by the actual hardware. Privileged instructions do have to be trapped for special treatment, and devices may be extensively emulated, depending on what they are. Notably, an OS X file is made to act like a hardware disk drive.
- With Boot Camp, there's no emulation or virtualization. The iMac simply runs as a native Intel-based Windows computer, with OS X completely out of the picture. However, under OS X, the Windows partition shows up in the Finder just as an external drive would, without your having to do any set up at all. Seeing all those weird Windows file and folder names on the Mac is a bit disconcerting. But very useful. (The Mac partition does not show up under Windows, although drivers or utilities that make it show up might exist. I didn't look for any.)
- Parallels doesn't emulate a dual-core chip. So, you don't get multi-processing regardless of what OS you're running on the virtualized machine. Since Boot Camp is entirely native, you get whatever the OS is capable of doing with a dual-core chip. I understand that Windows XP Professional can exploit this. Since I installed the Home edition, I wasn't able to check.
- I understand that you can install other OSes on the Boot Camp partition, but I didn't try that, and I have no idea what drivers might be available. Unfortunately, as far as I can determine, you can have only a single partition other than the native OS X partition, so you can't create a multi-boot machine--just a dual-boot. So, to test Linux, say, I would have had to wipe out my Windows partition, and I wasn't curious enough to do that.
- Parallels runs really well, seems solid, and is enormously convenient. But, the mouse seemed a little jerky. Maybe if I'd tried a different mouse or played around with the settings I could have fixed the problem. A worse limitation is that the machine is very slow. A quick test that involved a lot of disk I/O showed that it's 2+ times slower than the native machine (the Boot Camp approach). (A CPU-bound benchmark might perform OK, but that's unrealistic for the way I use a computer.) Also, you can never get even close to the full amount of real memory for a Parallels machine. I have 1.5GB on my iMac, but 1GB is the most I could allocate with Parallels.
- I couldn't get Ubuntu 6.06 to install on a Parallels machine, even after reading some hints I found with Google and playing around with all sorts of settings. However, Gentoo installed perfectly and ran. As I said, I didn't try either in the Boot Camp partition.
- Conclusion: Boot Camp gives you an excellent Windows computer, and the hardware is completely reliable and predictable. Parallels gives you something that's slower, less usable, but wonderfully convenient. I expect that I'll be using the Boot-Camp installation of Windows on my iMac a lot, and that I'll soon put Parallels aside once the novelty has worn off.