The relationship between software defects and failures is not one-to-one. Some defects remain undis-covered and never cause a failure, but a single defect can cause many failures.

Many researchers have offered solutions to this problem, but their approaches typically reflect only the developer view of software reliability: how to predict and prevent the underlying defects. At Hewlett-Packard's Non-Stop Enterprise Division, researchers augment their defect-prevention activities with analyses of what their customers experience: software failures. NED provides customers with a regularly updated suite of hardware and software products for business-critical applications, then tracks the failure rate for each version so that it can measure the customer experience with that update.