s ▁may ▁occur ▁in ▁the ▁middle ▁of ▁long ▁instructions ▁and ▁the ▁state ▁de als ▁with ▁that ▁possibility . ▁ ▁Basic ▁mode ▁is ▁another ▁whole ▁form ▁of ▁instruction ▁formats ▁and ▁address ing . ▁ ▁Basic ▁mode ▁provides ▁compatibility ▁with ▁previous ▁systems ▁back ▁to ▁the ▁ 1 1 0 8 . ▁ ▁For ▁all ▁practical ▁purposes , ▁the ▁hardware ▁architecture ▁defines ▁the ▁rules ▁by ▁which ▁addresses ▁and ▁instructions ▁are ▁converted ▁to ▁the ▁above ▁forms . ▁ ▁The ▁most ▁obvious ▁difference ▁in ▁basic ▁mode ▁is ▁the ▁lack ▁of ▁explicit ▁B ▁registers ▁in ▁instructions . ▁ ▁Instead ▁there ▁are ▁four ▁implicitly ▁used ▁B ▁registers ▁( B 1 2 - B 1 5 ). ▁ ▁There ▁is ▁a ▁complex ▁algorithm ▁using ▁the ▁limits ▁of ▁the ▁banks ▁represented ▁by ▁those ▁B ▁registers , ▁the ▁oper and ▁address ▁and ▁the ▁B ▁register ▁within ▁which ▁the ▁current ▁instruction ▁is ▁found . ▁ ▁The ▁most ▁interesting ▁instructions ▁in ▁the ▁ 2 2 0 0 ▁re per toire ▁are ▁the ▁lock ing ▁and ▁synchron ization ▁instructions . ▁ ▁Cond itional ▁replace ▁is ▁familiar ▁and ▁quite ▁similar ▁to ▁Comp are ▁and ▁Sw ap ▁in ▁the ▁Intel ▁architecture . ▁ ▁These ▁instructions ▁always ▁gain ▁exclusive ▁use ▁of ▁the ▁memory / cache - line ▁holding ▁the ▁referenced ▁word . ▁ ▁T S ▁and ▁T SS ▁check ▁a ▁bit ▁in ▁the ▁referenced ▁word . ▁ ▁If ▁the ▁bit ▁is ▁clear , ▁they ▁set ▁it ▁and ▁continue ▁( TS ) ▁or ▁skip ▁( T SS ). ▁ ▁If ▁the ▁bit ▁is ▁set , ▁they ▁either ▁interrupt ▁( TS