reference will now be made in detail to the present preferred embodiments of the invention , examples of which are illustrated in the accompanying drawings . wherever possible , the same reference numbers are used in the drawings and the description to refer to the same or like parts . fig1 illustrates a top view of an american keyboard . fig2 illustrates a top view of a major keypad area of a japanese keyboard . fig3 illustrates a top view of a major keypad area of a korean keyboard . the embodiment discussed below provides a universal upper housing and key caps to at least satisfy keyboards as illustrated in fig1 - 3 . this embodiment focuses on how a key row 102 a of the american keyboard , a key row 104 a of the japanese keyboard and a key row 106 a of the korean keyboard share a common universal upper housing . other key rows of a major keypad area 102 of the american keyboard , a major keypad area 104 of the japanese keyboard and a major keypad area 106 of the korean keyboard already have a common design on the upper housing . as illustrated in fig1 ˜ 3 , the major differences among the key row 102 a , the key row 104 a and the key row 106 a are the space keys and their adjacent keys . how the universal upper housing and key caps be designed to form a universal keyboard is described below . fig4 a illustrates a top view of an upper housing of a universal keyboard . a major keypad area 202 of the universal upper housing 200 has a plurality of key holes , wherein a key hole row 202 a has been redesigned . the key hole row 202 a includes a space key hole 206 , which has the same diameter as other standard key holes ( the key holes not located in the key hole row 202 a ) does . a pair of assist holes 208 a / 208 b are located on two opposite sides of the space key hole 206 along the key hole row 202 a . the assist holes 208 a / 208 b are of smaller hole size or smaller diameter compared to the other standard key holes or the space key hole 206 . a pair of special key holes 204 a / 204 b are also located on two opposite sides of the space key hole 206 along the key hole row 202 a . the special key holes 204 a / 204 b are of larger hole size or larger diameter compared to the other standard key holes or the space key hole 206 . the assist hole 208 a is located between the space key hole 206 and the special key hole 204 a . the assist hole 208 b is located between the space key hole 206 and the special key hole 204 b . the following paragraphs are to describe that how american , japanese and korean key caps are designed to be installed on the key hole row 202 a of the universal upper housing 200 . please refer to fig1 , fig4 b and fig5 , which illustrates how american key caps are designed to be installed on the key hole row 202 a of the universal upper housing 200 . fig4 b illustrates a top view of the upper housing 200 , where a balance rod 210 is added . fig5 illustrates a top view 112 a , a bottom view 112 b and a side view 112 c of the american space key cap 112 . referring to fig5 , the american space key cap 112 has a main positioning pin 113 a , a pair of balance rod hooks 113 b and a pair of assist positioning pins 113 c on its bottom surface . the main positioning pin 113 a is located on a central area of the bottom surface . the pair of balance rod hooks 113 b are symmetrically located at two opposite sides of the main positioning pin 113 a . the pair of t - shaped assist positioning pins 113 c are also symmetrically located at two opposite sides of the main positioning pin 113 a . please refer to fig4 b and fig5 . when the american space key cap 112 is installed on the key hole row 202 a of the universal upper housing 200 , the main positioning pin 113 a is inserted into the space key hole 206 , the pair of assist positioning pins 113 c are respectively inserted into the special key holes 204 a / 204 b , and the pair of balance rod hooks 113 b respectively engage with two end portions 210 a / 210 b of the balance rod 210 . after the main positioning pin 113 a is inserted into the space key hole 206 , a pair of hooks 113 d engage with an inner wall of the space key hole 206 to secure the american space key cap 112 to the universal upper housing 200 . the balance rod 210 and the pair of assist positioning pins 113 c both result in a balanced action of the american space key cap 112 pressed by a user . please refer to fig2 , fig4 c fig6 and fig8 , which illustrates how japanese key caps are designed to be installed on the key hole row 202 a of the universal upper housing 200 . fig4 c illustrates a top view of the upper housing 200 , where a balance rod 212 is added . fig6 illustrates a top view 114 a , a bottom view 114 b and a side view 114 c of the japanese space key cap 114 . fig8 illustrates a top view 118 a , a bottom view 118 b and a side view 118 c of the japanese special key cap 118 . referring to fig6 , the japanese space key cap 114 has a main positioning pin 115 a , a pair of balance rod hooks 115 b and a pair of assist positioning pins 115 c on its bottom surface . the main positioning pin 115 a is located on a central area of the bottom surface . the pair of balance rod hooks 115 b are symmetrically located at two opposite sides of the main positioning pin 115 a . the pair of cylindrical assist positioning pins 115 c are also symmetrically located at two opposite sides of the main positioning pin 115 a . please refer to fig4 c and fig6 . when the japanese space key cap 114 is installed on the key hole row 202 a of the universal upper housing 200 , the main positioning pin 115 a is inserted into the space key hole 206 , the pair of assist positioning pins 115 c are respectively inserted into the assist holes 208 a / 208 b , and the pair of balance rod hooks 115 b respectively engage with two end portions 212 a / 212 b of the balance rod 212 . after the main positioning pin 115 a is inserted into the space key hole 206 , a pair of hooks 115 d engage with an inner wall of the space key hole 206 to secure the japanese space key cap 114 to the universal upper housing 200 . the balance rod 212 and the pair of assist positioning pins 115 c both result in a balanced action of the japanese space key cap 114 pressed by a user . please refer to fig4 c and fig8 . when a japanese special key cap 118 is installed on the key hole row 202 a of the universal upper housing 200 , a positioning pin 119 is inserted into the special key hole 204 a or 204 b , a pair of hooks 119 a engage with an inner wall of the special key hole 204 a or 204 to secure the japanese special key cap 118 to the universal upper housing 200 . the japanese special key cap 118 has bigger positioning pin 119 ( compared to main positioning pin of the space key cap ), which results in a balanced action of the japanese special key cap 118 pressed by a user . please refer to fig3 , fig4 b , fig7 and fig9 , which illustrates how korean key caps are designed to be installed on the key hole row 202 a of the universal upper housing 200 . fig4 b illustrates a top view of the upper housing 200 , where a balance rod 210 is added . fig7 illustrates a top view 116 a , a bottom view 116 b and a side view 116 c of the korean space key cap 116 . fig9 illustrates a top view 120 a and a bottom view 120 b of the korean special key cap 120 . referring to fig7 , the korean space key cap 116 has a main positioning pin 117 a , a pair of balance rod hooks 117 c and a pair of assist positioning pins 117 b on its bottom surface . the main positioning pin 117 a is located on a central area of the bottom surface . the pair of balance rod hooks 117 c are symmetrically located at two opposite sides of the main positioning pin 117 a . the pair of cylindrical assist positioning pins 117 b are also symmetrically located at two opposite sides of the main positioning pin 117 a ( a width between two assist positioning pins 117 b of the korean space key cap 116 is equal to a width between two assist positioning pins 115 c of the japan space key cap 114 ). please refer to fig4 b and fig7 . when the korean space key cap 116 is installed on the key hole row 202 a of the universal upper housing 200 , the main positioning pin 117 a is inserted into the space key hole 206 , the pair of assist positioning pins 117 b are respectively inserted into the assist holes 208 a / 208 b , and the pair of balance rod hooks 117 c respectively engage with two end portions 210 a / 210 b of the balance rod 210 . after the main positioning pin 117 a is inserted into the space key hole 206 , a pair of hooks 117 d engage with an inner wall of the space key hole 206 to secure the korean space key cap 116 to the universal upper housing 200 . the balance rod 210 and the pair of assist positioning pins 117 b both result in a balanced action of the korean space key cap 116 pressed by a user . please refer to fig4 b and fig9 . when a korean special key cap 120 is installed on the key hole row 202 a of the universal upper housing 200 , a positioning pin 121 is inserted into the special key hole 204 a or 204 b , a pair of hooks 121 a engage with an inner wall of the special key hole 204 a or 204 to secure the korean special key cap 120 to the universal upper housing 200 . the korean special key cap 120 has bigger positioning pin 121 ( compared to main positioning pin of the space key cap ), which results in a balance pressed action of the korean special key cap 120 by a user . in addition , the positioning pin 121 of the korean special key cap 120 is of the same size as the positioning pin 119 of the japanese special key cap 118 , such that both the positioning pin 121 and the positioning pin 119 can be both inserted into the special key hole 204 a / 204 b . according to embodiments discussed above , the universal keyboard has a universal upper housing for installing at least american , japanese and korean key caps , thereby reducing manufacturing costs . it will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention . in view of the foregoing , it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents .