▁later ▁bought ▁by ▁the ▁T andy ▁( now ▁Radio Sh ack ) ▁Corporation . ▁ ▁The ▁Grid ' s ▁port ability ▁was ▁restricted ▁as ▁it ▁had ▁no ▁internal ▁battery ▁pack ▁and ▁re lied ▁on ▁main s ▁power . ▁ ▁D ul mont ▁Mag num / K ook ab ur ra ▁ ▁The ▁first ▁cont ender ▁for ▁true ▁laptop ▁computing ▁was ▁the ▁ 1 6 - bit ▁D ul mont ▁Mag num , ▁designed ▁by ▁David ▁Ir win ▁and ▁John ▁Bla ir ▁of ▁D ul m ison , ▁Australia , ▁in ▁ 1 9 8 2 ▁and ▁released ▁in ▁Australia ▁in ▁September ▁ 1 9 8 3 ▁by ▁D ul mont . ▁This ▁battery - power ed ▁device ▁included ▁an ▁ 8 0 ▁character ▁× ▁ 8 ▁line ▁display ▁in ▁a ▁lid ▁that ▁closed ▁against ▁the ▁keyboard . ▁ ▁The ▁D ul mont ▁was ▁thus ▁the ▁first ▁computer ▁that ▁could ▁be ▁taken ▁anywhere ▁and ▁offered ▁significant ▁computing ▁potential ▁on ▁the ▁user ' s ▁laptop ▁( though ▁we igh ing ▁in ▁at ▁ 4 . 8   kg ). ▁ ▁It ▁was ▁based ▁on ▁the ▁MS - D OS ▁operating ▁system ▁and ▁applications ▁stored ▁in ▁R OM ▁( A :) ▁and ▁also ▁supported ▁remov able ▁modules ▁in ▁expansion ▁sl ots ▁( B : ▁and ▁C :) ▁that ▁could ▁be ▁custom ▁program med ▁EP ROM ▁or ▁standard ▁word ▁processing ▁and ▁spread sheet ▁applications . ▁ ▁The ▁Mag num ▁could ▁susp end ▁and ▁retain ▁memory ▁in ▁battery - back ed ▁C M OS ▁RAM , ▁including ▁a