MDI Client uses the older Multi Document Interface for Windows, which displays the grey background window within which all Big Business windows are displayed.
The new standard Client for Big Business for Windows uses SDI, Single Document Interface, which is the modern standard.
If for some reason you need the old look we can build this. It is not a standard offering and is not included included in our standard testing cycle. It should work perfectly well for some time but will not prompt changes that contravene new standards.