▁were ▁ 7 5 ▁of ▁these ▁circuit ▁bo ards ▁and ▁each ▁one ▁was ▁co ated ▁with ▁a ▁flexible ▁poly ure th ane ▁comp ound ▁for ▁mo ist ure ▁and ▁v ibration ▁protection . ▁The ▁high ▁degree ▁of ▁reli ability ▁and ▁rug ged ness ▁of ▁the ▁computer ▁were ▁driven ▁by ▁the ▁strict ▁requirements ▁of ▁the ▁weapons ▁system . ▁ ▁Design ▁constraints ▁High ▁reli ability ▁was ▁required ▁of ▁the ▁D - 1 7 B . ▁It ▁controlled ▁a ▁key ▁weapon ▁that ▁would ▁have ▁just ▁one ▁chance ▁to ▁execute ▁its ▁mission . ▁R eli ability ▁of ▁the ▁D - 1 7 B ▁was ▁achieved ▁through ▁the ▁use ▁of ▁solid - state ▁electron ics ▁and ▁a ▁relatively ▁simple ▁design . ▁Sim pler ▁D RL ▁( di ode – res istor ) ▁logic ▁was ▁used ▁extens ively , ▁but ▁less - re li able ▁D TL ▁( di ode – trans istor ) ▁logic ▁was ▁used ▁only ▁where ▁needed . ▁In ▁the ▁late ▁ 1 9 5 0 s ▁and ▁early ▁ 1 9 6 0 s , ▁when ▁the ▁D - 1 7 B ▁was ▁designed , ▁trans ist ors ▁lack ed ▁today ' s ▁reli ability . ▁D TL ▁provided , ▁however , ▁either ▁gain ▁or ▁in version . ▁R eli ability ▁was ▁also ▁en hanced ▁by ▁the ▁rot ating - disk ▁memory ▁with ▁non - dest ruct ive ▁read out ▁( ND RO ). ▁In ▁actual ▁real - time ▁situations , ▁Min ut eman ▁miss iles ▁achieved ▁a ▁mean ▁time ▁between ▁fail ures ▁( MT