More detail about depth buffer

Hi,

First, thanks for providing this great platform.
I have some question related to the "depth buffer" as following:

1. In depth buffer, what is the resolution have? I saw the "seta r_depthbits "0"" in quake3 config file "assets/q3config.cfg". Is it 8 bit by default? Can we change the setting to a 16 bit to increase the dynamic range?

2. How to convert the values in the depth buffer to real depth in the game world?

I will be very thankful if anyone can help me =)