I used to use Microsoft Virtual PC 2004 on my work PC (e.g. running my work environment inside a VM so that I can easily resurrect it after a rebuild) but I found that performance was abysmal after I resumed from hibernation. Well, it seems it wasn’t just me having issues and Thomas Lee reports that Microsoft knowledge base article 889677 describes a hotfix for the issue. Nowadays I’m using Microsoft Virtual Server 2005 on a Windows Server 2003 SP1 machine and having performance issues when I run more than one VM (each guest is slow to respond to keyboard/mouse actions). In fairness, the host is a notebook PC, and it is running Windows SharePoint Services too, but there are no performance issues on the host – just the guests. It would seem logical to suspect a slow laptop hard disk as the cause, but there are no obvious signs of large amounts of disk activity. John Howard blogged about performance when running Windows Server 2003 SP1 as a guest, but I can’t find anything about poor host performance. I guess I’ll have to wait for Virtual Server 2005 service pack 1.