Adapter Performance Requirements
One of the goals of the Windows Biometric Framework is to give users a delightful experience by making sure the system responds to them quickly. The delay experienced by users is directly related to the amount of time it takes for each adapter routine to execute. Consequently, adapter writers should optimize their code for quick execution.
Because the objective is fast response overall, the performance of an adapter isn't specified in terms of time limits on specific routines. Instead, performance is specified as a set of requirements for the overall user experience.
There are two requirements:
- Any interaction between the user and the operating system that involves biometrics must complete within two seconds. That interval measures the start-to-finish time that the user perceives from the time they touch or swipe the sensor until the time something visible happens on the device screen. (For example, during unlock, there must be no more than a two-second delay between the user touching or swiping the fingerprint sensor and the lock screen acknowledging the user's identity.)
- For the initial appearance of credential tiles on the sign-in or lock screen, we allow a little more time (three seconds, maximum), but we still prefer sooner rather than later. Specifically, the bio tile needs to be visible on screen within three seconds of the appearance of the lock or sign-in panel.
These numbers are not arbitrary. Numerous studies have shown that human beings tend to experience everything that happens within a two-second interval as part of the "now" moment. If event A and event B happen within two seconds of each other, people perceive those events as being simultaneous. If the events are separated by more than about three seconds, people think there's a delay—they feel that something is "taking too long." So this is an issue of hardwired human psychology.