This leads to big units of code, namely multiple OSes, whereas the ideal is being able to use as finely granular units as developers are able to stomach. For ex

This leads to big units of code, namely multiple OSes, whereas the ideal is being able to use as finely granular units as developers are able to stomach. For example, Xen can work around the issue of device drivers by hosting a minimal OS instance that has drivers, but it is better to be able to run drivers as individual processes. This reduces code duplication and performance overhead.