Dan Gillmor has eloquently condemned Virtual PC 5 for OS X as betaware masquerading as a commercial product. I'm not quite as harsh, because I needed Virtual PC for OS X, and this was at least something that worked, if not well. A public beta, such as that being run by Dantz for Retrospect for OS X, would have been more appropriate.
For those of you who have come in late, Virtual PC is an emulator that allows the Mac to pretend its got an Intel processor beating inside a software application that uses disk images to create operating system installations. It works great under OS 9, but Connectix said (and I believe them) that OS X had engineering hurdles for them to steal enough processing power to get VPC to run as well. OS X is so even-handed, the product manager told me at Macworld in January, that they have to play a lot of games to get more cycles without disrupting the OS.
This is all well and good, and sounds true from all accounts. But this doesn't explain why they shipped a product that ran at such a slow speed that you could hear pixels being redrawn. On my 450 MHz G4 Cube with 1.5 Gb of RAM, Windows 98 ran so slow that I could double click and could to 60 before a My Computer window would open. Connectix traded revenue for hostility.
Today, they shipped the 5.0.2 update for Virtual PC, and it makes a huge difference. I'm seeing a factor of 2 to about 100 (literally) depending on the activity. It is now usable, although still slow. I was able to install Windows XP Home Edition without a hitch, although I had a few odd crashes after configuring it.
The new version of VPC uses a kind of roll-back technique in which changes to the hard disk are written as difference records and the emulator's volume bitmap points to these fragments. It's clever as it doesn't increase the size of the partition much. VPC already only uses as much storage for a hard disk as it needs: create a 10 Gb drive with 2 Gb on it, and VPC only uses 2 Gb but expands it automatically as the system requires it. You can then commit changes or roll back as you save or close out sessions.
Virtual PC is a critical component of OS X's dominance. I wrote a column recently about the three-headed monster that OS X had become: it allows you to run native Unix programs, Classic and native Mac OS program (9 and X, and some programs dating back 10 years!), and with VPC, any Windows or Intel-based OS's and programs. Why get a PC with one OS when you could get several with OS X?