Reuters

Indonesian authorities have retrieved one of two black boxes, the Flight Data Recorder, from a Sriwijaya Air Boeing 737-500 that crashed into the Java Sea on Saturday.
WHAT ARE BLACK BOXES?
They are not actually black but high-visibility orange. Many historians attribute their invention to Australian scientist David Warren in the 1950s. They are mandatory. The aim is not to establish legal liability, but to identify causes and help prevent future accidents.
HOW HAVE THEY EVOLVED?
The earliest devices recorded limited data on wire or foil. Models like those typically found on the 1980s-designed Boeing 737-50 use magnetic tape. Modern ones use computer chips. The recordings are housed inside crash-survivable containers able to withstand 3,400 times the force of gravity on impact.
HOW BIG ARE THEY?
They weigh about 10 pounds (4.5 kilos) and contain four main parts: chassis or interface designed to fix the device and facilitate recording and playback, an underwater locator beacon, the core housing or ‘Crash-Survivable Memory Unit’ made of stainless steel or titanium, inside there, the recordings on chips or older formats. There are two recorders: a Cockpit Voice Recorder (CVR) for pilot voices or cockpit sounds, and a Flight Data Recorder (FDR).
HOW WILL THE RECORDERS BE HANDLED?
After a crash over the sea, the recorder is placed back in water to prevent damage from contact with air while being transported. Once dry, technicians peel away protective material and carefully clean and retrieve the recordings, which are copied.
HOW MUCH INFORMATION IS AVAILABLE?
The FDR contains about 25 hours of data on eight tracks and the CVR has 30 minutes of conversation.
WHERE WILL THE DATA BE READ?
Indonesian officials leading the probe have said they plan to perform the readout at their facilities. If recorders are badly damaged, the operation is occasionally delegated to an overseas agency like France’s BEA or the device’s manufacturer.