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One of the most crucial tools in our toolbox is VMware Workstation, which I've been recommending for years. The basic idea is that it lets you run a whole PC inside a window, with its own operating system and hard drive. Here's an old picture so you get the general idea:

Since 4.0 you've been able to run multiple machines in tabs, a nice addition.

Anyway, they've recently released version 5.0, which is a big leap forward. It has the very slick ability to store multiple snapshots and build up a tree of systems with slightly different configurations, sort of like object-oriented inheritence. That saves a ton of disk space when you need to test systems with only small variations.

Here's an example. The first thing that FogBugz Setup does when you run it is to test that all kinds of prerequisites are installed, like IIS and MDAC and VBScript. In order to develop and test that code, I need virtual machines that are missing the prerequisites, so I can test all the code paths.

With VMware 5, I can build a stripped down virtual machine containing, say, a minimum Windows 2000 installation without any of the prerequisites. Then I can take a snapshot of that, and install prerequisite 1. Then I can take another snapshot of that, and install the prerequisite 2. Eventually I end up with a bunch of snapshots with different configurations and I can go back or forwards to a particular configuration in one step.

Here's another example of why VMware is critical. Let's say I'm testing the upgrade code in FogBugz for upgrading, say, from FogBugz 2.0 to FogBugz 4.0. In about one minute I can be running a pristine copy of Windows 2000 that looks just like the day it was installed. Two minutes later, it's running FogBugz 2.0, and I take another snapshot. Now I run my upgrade code on that, and, of course, it fails, thanks to Murphy's law, but it leaves FogBugz in a "half-upgraded" state. The brilliant part of VMware is that I can click to go back to the 2.0 snapshot and in about 30 seconds I'm back to a pristine FogBugz 2.0 installation.

Our other major use for VMware at Fog Creek is for supporting Linux. FogBugz runs on all kinds of different distros and we use VMs to develop and test with them all.

Over the coming months our four summer interns are going to be developing a product that requires a server and two clients, so we'll need three VMs to simulate the complete environment. We bought high-end, dual-Xeon Dell workstations with dual monitors and 2 GB of memory each (that's our new standard developer workstation) which will make it easy and fast to simulate the complete production environment on every intern's computer. It's probably overkill and you can run VMware happily on less pumped-up computers, but if you're simulating a network of three machines VMware definitely benefits from lots of RAM and CPUs.

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About the Author: I’m your host, Joel Spolsky, a software developer in New York City. Since 2000, I've been writing about software development, management, business, and the Internet on this site. For my day job, I run Fog Creek Software, makers of FogBugz—the smart bug tracking software with the stupid name, and Fog Creek Copilot—the easiest way to provide remote tech support over the Internet, with nothing to install or configure.

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