My answer to Why are black boxes on airplanes relying on such old technology?
Answer by Thomas Zerbarini:
Modern black boxes are digital solid state recorders. They are know as digital flight data recorder (DFDR) and a digital cockpit voice recorder (DCVR).
The DFDR can record up to 25 hours of information on the aircraft systems, instruments, flight conditions, etc… for investigators or safety officers to reconstruct and accident or incident.
The DCVR can record up to 2 hours of voice and sound in the cockpit and on the radio /inter-phone communications.
Here is a great explanation on how the DFDR and DCVR work.
This is a good video covering the basics of what these recorders do, how they work, and how they are designed and tested”
In the United States, this recorded information is strictly used for investigation and safety education. The recordings cannot be used for disciplinary actions. The premise is that we want the information for safety and we strictly use it for safety by uncovering patterns and behaviors that may cause accidents/incidents. We use it to learn from mistakes.