At first glance it looks like little more than just another 4-bay NAS appliance, but the Sentinel DX4200 from Western Digital stands out from the crowd both in terms of the hardware involved and the Windows rather than Linux software it runs. Moreover, the DX4200 is very much aimed at businesses with existing Windows servers and expertise looking to add flexible network storage to the mix.A proper server in a boxHoused in a conventional desktop NAS cube, the DX4200 eschews the plastic panels found on lesser consumer products in favour of a solid, all-metal, construction. A somewhat bulky AC brick provides the power and, although only one PSU comes as standard, another can be purchased and plugged in to keep the appliance running should either of the pair suffer a failure.A large and quite noisy single fan located at the rear keeps the unit nice and cool with a couple of Gigabit network ports above, together with four USB 3.0 ports that can be used to attach external backup drives. You can also plug in a keyboard and mouse, and a screen via the VGA port alongside, to directly manage the DX4200 just as you would a standard Windows server. When not doing that, however, a small LCD panel at the front summarises what's going on inside with, underneath, a lockable door behind which the storage lies and it's here that things start to get interesting.