title: device driver stack
body: <p>I'm a beginner and I'm trying to understand the concept behind the device driver stack? I know the device driver stack has three layers named low level driver, bus manager and a high level driver. 
  My question is this, Is there separate codes exist for low level driver and bus manager? If they exist, where can I find the low level drivers for hardware controllers in a Linux file system?
  Thanks.</p>