A system unit is a unit of measurement for computer hardware. One system unit is equal to the amount of a particular type of measure necessary to fill one paper, card, or other object meant for insertion into a file folder.
A standard letter-sized file folder would require approximately 100 sheets or ten cards to fill it, hence each sheet’s dimensions are approximately 187 millimeters by 127 millimeters (roughly 7 inches by 5 inches), which is measured out in centimeters will be 10×7 cm. Thus, there are 1000 system units in this paper size/card size combined with that file folder’s width and height measurements. These 1000 System Units equate to 1 U in metric terms with the system unit being .1 m² in area equivalent.