▁means ▁of ▁connection ▁and ▁the ▁software ▁to ▁access ▁it ▁is ▁also ▁relatively ▁simple , ▁although ▁need ing ▁to ▁be ▁written ▁for ▁specific ▁computers ▁and ▁their ▁serial ▁ports . ▁ ▁Prop ri et ary ▁interfaces ▁ ▁There ▁are ▁a ▁few ▁other ▁less ▁common ▁interfaces . ▁These ▁were ▁used ▁in ▁large ▁EP OS ▁systems ▁with ▁dedicated ▁hardware , ▁rather ▁than ▁att aching ▁to ▁existing ▁comm od ity ▁computers . ▁In ▁some ▁of ▁these ▁interfaces , ▁the ▁sc anning ▁device ▁returned ▁a ▁" raw " ▁signal ▁proportional ▁to ▁the ▁intens ities ▁seen ▁while ▁sc anning ▁the ▁bar code . ▁This ▁was ▁then ▁dec oded ▁by ▁the ▁host ▁device . ▁In ▁some ▁cases ▁the ▁sc anning ▁device ▁would ▁convert ▁the ▁sym b ology ▁of ▁the ▁bar code ▁to ▁one ▁that ▁could ▁be ▁recognized ▁by ▁the ▁host ▁device , ▁such ▁as ▁Code ▁ 3 9 . ▁ ▁Key board ▁w edge ▁( e . g . ▁PS / 2 ) ▁▁ ▁With ▁the ▁popular ity ▁of ▁the ▁PC ▁and ▁its ▁standard ▁keyboard ▁interface , ▁it ▁became ▁ever ▁easier ▁to ▁connect ▁physical ▁hardware ▁to ▁a ▁PC ▁and ▁so ▁there ▁was ▁commercial ▁demand ▁similarly ▁to ▁reduce ▁the ▁complexity ▁of ▁the ▁associated ▁software . ▁" Key board ▁w edge " ▁hardware ▁plug ged ▁between ▁the ▁PS / 2 ▁port ▁and ▁the ▁keyboard , ▁with ▁characters ▁from ▁the ▁bar code ▁sc anner ▁appearing ▁exactly ▁as ▁if ▁they ▁had ▁been ▁typed ▁at ▁the ▁keyboard . ▁This ▁made ▁the ▁addition ▁of ▁simple ▁bar code ▁reading ▁ab ilities ▁to ▁existing ▁programs ▁very ▁easy , ▁without