9 6 0 s ▁before ▁being ▁replaced ▁by ▁the ▁similar - in - name - only ▁UN IV AC ▁ 1 1 0 0 ▁family . ▁ ▁Description ▁ ▁This ▁computer ▁was ▁ ▁long , ▁ ▁wide , ▁we ighed ▁about ▁ ▁and ▁used ▁ 2 7 0 0 ▁vac u um ▁tub es ▁for ▁its ▁logic ▁circ uits . ▁Its ▁drum ▁memory ▁was ▁ ▁in ▁diameter , ▁rot ated ▁at ▁ 3 5 0 0 ▁r pm , ▁had ▁ 2 0 0 ▁read - write ▁heads , ▁and ▁held ▁ 1 6 , 3 8 4 ▁ 2 4 - bit ▁words ▁( a ▁memory ▁size ▁equivalent ▁to ▁ 4 8 ▁kB ) ▁with ▁access ▁time ▁between ▁ 3 2 ▁micro seconds ▁and ▁ 1 7 ▁mill iseconds . ▁ ▁Inst ru ctions ▁were ▁ 2 4 ▁bits ▁long , ▁with ▁six ▁bits ▁for ▁the ▁op code , ▁four ▁bits ▁for ▁the ▁" skip " ▁value ▁( t elling ▁how ▁many ▁memory ▁locations ▁to ▁skip ▁to ▁get ▁to ▁the ▁next ▁instruction ▁in ▁program ▁sequence ), ▁and ▁ 1 4 ▁bits ▁for ▁the ▁memory ▁address . ▁Num bers ▁were ▁binary ▁with ▁negative ▁values ▁in ▁ones ' ▁complement . ▁The ▁addition ▁time ▁was ▁ 9 6 ▁micro seconds ▁and ▁the ▁multiplication ▁time ▁was ▁ 3 5 2 ▁micro seconds . ▁ ▁The ▁single ▁ 4 8 - bit ▁accum ulator ▁was ▁fund ament ally ▁subtract ive , ▁addition ▁being ▁carried ▁out ▁by ▁subtract ing ▁the ▁ones ' ▁complement ▁of ▁the ▁number ▁to ▁be