▁by ▁Gold man ▁Sach s ▁Group ▁Inc . ▁Dark ▁po ols ▁operated ▁by ▁other ▁prominent ▁banks ▁and ▁trad ing ▁fir ms ▁such ▁as ▁Well s ▁F argo ▁and ▁Cit adel ▁L LC ▁were ▁also ▁non ▁oper ational ▁for ▁periods ▁of ▁the ▁free ze . ▁These ▁dark ▁po ols ▁are ▁not ▁the ▁juris diction ▁of ▁the ▁Nas da q ▁or ▁the ▁NY SE ▁but ▁are ▁reli ant ▁on ▁accurate ▁quotes ▁being ▁issued ▁on ▁stock s ▁listed ▁on ▁either ▁exchange ▁and ▁therefore ▁cannot ▁operate ▁when ▁Nas da q ▁stock s ▁cannot ▁be ▁trad ed . ▁ ▁C ause ▁ ▁Prior ▁to ▁a ▁public ▁statement ▁made ▁by ▁Nas da q ▁O M X ▁released ▁on ▁the ▁evening ▁of ▁August ▁ 2 2 , ▁there ▁was ▁spec ulation ▁in ▁financial ▁mark ets ▁as ▁to ▁the ▁cause ▁of ▁the ▁out age . ▁Some ▁media ▁out lets ▁suggested ▁that ▁the ▁out age ▁was ▁caused ▁by ▁a ▁coding ▁error , ▁while ▁others ▁spec ulated ▁that ▁hack ing ▁could ▁have ▁been ▁the ▁cause . ▁ ▁The ▁cause ▁of ▁the ▁out age ▁was ▁identified ▁as ▁being ▁a ▁capacity ▁issue ▁with ▁the ▁Nas da q ▁S IP . ▁A ▁capacity ▁assess ment ▁had ▁been ▁run ▁on ▁the ▁S IP ▁in ▁January ▁ 2 0 1 3 ▁which ▁found ▁that ▁each ▁of ▁the ▁ 5 0 ▁ports ▁in ▁the ▁system ▁could ▁toler ate ▁ 1 0 , 0 0 0 ▁items ▁per ▁second , ▁meaning ▁the ▁whole ▁S IP ▁had ▁a ▁capacity ▁of ▁ 5 0 0 , 0 0 0 ▁items ▁per ▁second