Mobile network generations and bandwidth

I have couple of question related to mobile network generations:

1. While comparing generation of mobile network people mention that 1G and 2G has to use maximum bandwidth. What is bandwidth in this content and why they use maximum bandwidth?
2. 1G and 2G are narrow band networks. What is narrow band here?
3. 3G and 4G are wide band networks. Don't they use maximum bandwidth?

1. They use maximum bandwidth to transmit analogue voice information. Since available bandwidth is limited and there is a limit on the bandwidth needed to make the voice recognizable on the other side, they can't go below this fixed bandwidth.

2. It refers to the frequency span of the carrier. If it is narrow band, then usually it's just a few kilohertzes, which makes available bandwidth low (this also depends on the kind of modulation used).

3. They don't need the maximum available bandwidth for voice communications, since for an acceptable voice quality we need to transmit signals that encode just a few kilohertzes of analogue information.