 The front part of the case is occupied by an integrated 40 @-@ key membrane keyboard displaying 20 graphic and 54 inverse video characters . Each key has up to five functions , accessed via the <unk> and <unk> keys or depending on context . For example , the P key combined the letter P , the " character and the BASIC commands <unk> and TAB . The ZX81 uses a standard QWERTY keyboard layout . The keyboard is mechanically very simple , consisting of 40 pressure @-@ pad switches and 8 diodes under a plastic overlay , connected in a matrix of 8 rows and 5 columns . 
