I'm deeply fascinated by software instrumentation in all its varieties. When Scott Dart told me that he had hard data on how many people are using the tagging features in Photo Gallery, I wanted to know how. The answer is SQM, which is pronounced "squim" and which expands to Software Quality Metrics.

According to Partha Sundaram, my guest for today's podcast, SQM was formerly used on a per-application basis, but is now, in Vista, also a piece of core infrastructure that can be used to analyze how the operating system itself is being used in the field. He reviews the current use of SQM in Vista, and some future goals for the technology.