Different examples of mob environments exist, for example, Hunter Industries uses an open office environment, where each mob has its own area with desks facing several large hi-res screens, surrounded by whiteboards.

There is one computer with one keyboard, the team member who sits at the keyboard is known as the driver. The other members of the team are known as the navigators. There is room for others to sit at the desk, including the team coach.

For the mob to switch out drivers quickly, it's probably wise to be familiar with one IDE and set of tools. Although it's not impossible to have more than one IDE set up on a computer, there are benefits from everyone in the team using the same environment, knowledge sharing, for example. Reaching a consensus shouldn't be hard and the benefits of agreeing on one environment outweigh the potential pitfalls of many different setups.

Around the outside of their space, there are desks where team members can go to work if they are focussed on something else and don't want to work directly with the mob. In this way, they can still hear what the mob is up to without actively engaging. 

Of course, if people don't feel useful or dislike what they are contributing, they are allowed to leave the mob environment and take a break. 

It's a good idea to discuss beforehand how the team will work as a mob. Here is one team's working agreement for mob programming:

Mob etiquette:

• Core mob size: 3 to 4
• Need some way of letting people go and do their thing and then bring them up to speed when they rejoin.
• Define breakpoints, so we can have lunch, check emails, and perform admin tasks.
• Need to accommodate other work tasks, such as helping someone else.
• If we leave the Mob, we need to communicate what’s going on, not a permission slip but a courtesy.
• If we need to do something that isn't mob work, maybe step away from the mob. (It isn't fair to the rest of the mob if we're distracting them.)