▁and ▁the ▁internal ▁processor ▁was ▁interrupted ▁by ▁a ▁micro processor ▁based ▁device ▁which ▁em ulated ▁the ▁paper ▁t ape ▁reader ' s ▁signals , ▁but ▁which ▁had ▁a ▁serial ▁port ▁connected ▁to ▁the ▁D NC ▁system . ▁As ▁far ▁as ▁ ▁the ▁control ▁was ▁concerned , ▁it ▁was ▁receiving ▁from ▁the ▁paper ▁t ape ▁unit ▁as ▁it ▁always ▁had ; ▁in ▁fact ▁it ▁was ▁the ▁B TR ▁or ▁Re ader ▁Em ulation ▁card ▁which ▁was ▁transm itting . ▁A ▁switch ▁was ▁frequently ▁added ▁to ▁permit ▁the ▁paper ▁t ape ▁reader ▁to ▁be ▁used ▁as ▁a ▁backup . ▁▁ 1 9 9 0 s ▁to ▁present ▁The ▁PC ▁explos ion ▁in ▁the ▁late ▁ 1 9 8 0 s ▁and ▁early ▁ 1 9 9 0 s ▁sign alled ▁the ▁end ▁of ▁the ▁road ▁for ▁propriet ary ▁D NC ▁terminal s . ▁With ▁some ▁exceptions , ▁C NC ▁manufact ur ers ▁began ▁migr ating ▁to ▁PC - based ▁controls ▁running ▁D OS , ▁Windows ▁or ▁OS / 2 ▁which ▁could ▁be ▁linked ▁in ▁to ▁existing ▁networks ▁using ▁standard ▁protocol s . ▁Custom ers ▁began ▁migr ating ▁away ▁from ▁expensive ▁min ic om put er ▁and ▁work station ▁based ▁C AD / C AM ▁toward ▁more ▁cost - effect ive ▁PC - based ▁solutions . ▁Users ▁began ▁to ▁demand ▁more ▁from ▁their ▁D NC ▁systems ▁than ▁secure ▁upload / download ▁and ▁editing . ▁PC - based ▁systems ▁which ▁could ▁accomplish ▁these ▁tasks ▁based ▁on ▁standard ▁networks ▁began ▁to ▁be ▁available ▁at ▁minimal ▁or ▁no ▁cost