add adding-machine addition appearance bulky buttons calculate calculating calculations calculators clear Clearance computers computing digits handle heavy input large limitations limited machine numbers numerals office office-equipment output predating press pressing problem-solving problems slow subtract subtraction technology background computer feathers graphic texture chrome cooler desktop fan chip contacts cpu electronics gold pins processor studs cd dvd masterize movie music rom connection connector network rj45 COM parallel port switch keyboard mouse PS2 usb black byte data disc file floppy magnetic cable cables communication communications firewire laptop