▁are ▁" da isy ▁ch ained "; ▁and ▁one ▁interface ▁can ▁attach ▁up ▁to ▁eight ▁peri pher al ▁control ▁units . ▁The ▁last ▁control ▁unit ▁in ▁the ▁chain ▁must ▁have ▁a ▁termin ator ▁plug . ▁Each ▁control ▁unit ▁can ▁attach ▁a ▁number ▁of ▁devices , ▁" six teen ▁is ▁a ▁typical ▁number ." ▁There ▁is ▁an ▁architect ural ▁limit ▁of ▁ 2 5 6 ▁devices ▁per ▁channel , ▁and ▁initially ▁a ▁limitation ▁of ▁, ▁later ▁extended ▁to ▁, ▁between ▁the ▁main frame ▁and ▁the ▁control ▁unit . ▁Bus ▁and ▁Tag ▁channels ▁handle ▁data ▁rates ▁up ▁to ▁ 4 . 5   MB ▁per ▁second . ▁Only ▁one ▁device ▁can ▁transfer ▁data ▁at ▁a ▁time . ▁ ▁Bus ▁and ▁Tag ▁architecture ▁ ▁was ▁also ▁used ▁by ▁other ▁computer ▁manufact ur ers ▁to ▁attach ▁IBM ▁peri pher als ▁to ▁their ▁systems . ▁It ▁was ▁later ▁published ▁by ▁the ▁US ▁National ▁Techn ical ▁Information ▁Service ▁( NT IS ) ▁as ▁F IP S ▁P UB ▁ 6 0 - 1 , ▁I / O ▁Channel ▁Interface . ▁ ▁Bus ▁and ▁Tag ▁ ▁was ▁introduced ▁with ▁System / 3 6 0 ▁in ▁ 1 9 6 4 , ▁and ▁was ▁also ▁used ▁with ▁System / 3 7 0 . ▁With ▁the ▁introduction ▁of ▁serial , ▁fi ber ▁opt ic ▁ES CON ▁in ▁the ▁ 1 9 9 0 s ▁Bus ▁and ▁Tag ▁channels ▁were ▁re - ch rist ened ▁" parallel ▁channels ", ▁and ▁were ▁gradually ▁su pers eded . ▁" Par allel ▁channels ▁are ▁not ▁available