The larger one on the outside. That's because that's the one that is currently on the market right now, so I can speak first-hand on it.
You're looking at roughly 5,000 hours before a rebuild has to take place on that compressor module. Inside the housing, you actually have four components. There's a compressor module, controls module, electronics module, and the fan.
The operating part of the compressor itself, in the compression module, typically has a lifespan of about 5,000 hours, roughly 15,000 litres of fuel. After that lifespan of roughly 5,000 hours, you would change the compressor module.