19" rack units are an industry standard racking system - you get no bonus points for understanding that the equipment panel mounting width is 19". The capacity or height is measured in 'U' units (1U is 1 3/4"). Therefore a 12U rack mount unit has panel height of 21" with width 600mm and depth 430mm.
The wall mount 19" rack mount cupboards that we supply have removable side panels for ease of maintenance. Additionally the door can be removed, especially good for an intensive session of use.