s , ▁and ▁created ▁initial ▁bitmap ▁images ▁after ▁the ▁oct opus - like ▁al iens . ▁Other ▁al ien ▁designs ▁were ▁mode led ▁after ▁squ ids ▁and ▁c rab s . ▁The ▁game ▁was ▁originally ▁titled ▁Space ▁Mon sters ▁after ▁a ▁popular ▁song ▁in ▁Japan ▁at ▁the ▁time , ▁" Mon ster ", ▁but ▁was ▁changed ▁to ▁Space ▁Inv aders ▁by ▁the ▁designer ' s ▁super iors . ▁ ▁Hard ware ▁Because ▁micro comput ers ▁in ▁Japan ▁were ▁not ▁powerful ▁enough ▁at ▁the ▁time ▁to ▁perform ▁the ▁complex ▁tasks ▁involved ▁in ▁design ing ▁and ▁programming ▁Space ▁Inv aders , ▁N ish ik ado ▁had ▁to ▁design ▁his ▁own ▁custom ▁hardware ▁and ▁development ▁tools ▁for ▁the ▁game . ▁He ▁created ▁the ▁ar cade ▁board ▁using ▁the ▁latest ▁micro process ors ▁from ▁the ▁United ▁States . ▁The ▁game ▁uses ▁an ▁Intel ▁ 8 0 8 0 ▁central ▁processing ▁unit ▁( CP U ), ▁displays ▁r aster ▁graphics ▁on ▁a ▁C RT ▁monitor ▁using ▁a ▁bit ma pped ▁frame buffer , ▁and ▁uses ▁mon a ural ▁sound ▁hosted ▁by ▁a ▁combination ▁of ▁analog ▁circuit ry ▁and ▁a ▁Texas ▁Inst ru ments ▁SN 7 6 4 7 7 ▁sound ▁chip . ▁The ▁ad option ▁of ▁a ▁micro processor ▁was ▁inspired ▁by ▁Gun ▁Fight ▁( 1 9 7 5 ), ▁Mid way ' s ▁micro processor ▁adaptation ▁of ▁N ish ik ado ' s ▁earlier ▁discrete ▁logic ▁game ▁Western ▁Gun , ▁after ▁the ▁designer ▁was ▁im pressed ▁by ▁the ▁improved ▁graphics ▁and ▁sm o other ▁animation ▁of ▁Mid