Passenger Flight information displays

[subwayboy]

I am a very frequent PAX on the Tapei - HK - Tokyo routes,

I usually fly CX , but have been known to fly JAA, although I'm not to keen on flying in Aircraft which are older than me !!!

Anyway, my question

These in-flight displays with the maps, Altitude and current time to dest etc

how are the generated,

1. an independant GPS device + info from the planes on-board systems

2. Or just a sub-set of the information the pilot has access to ?

The time to destination info is usually very accurate, but is the altitude and head/tail / airspeed etc ?


thanks in advance

Paul (A systems engineer with a hatrid of flying)