▁in ▁later ▁available ▁P CI ▁Express ▁bus . ▁ ▁Some ▁non - P CI ▁architect ures ▁also ▁use ▁message ▁sign alled ▁interrupt s . ▁ ▁Over view ▁ ▁Trad itionally , ▁a ▁device ▁has ▁an ▁interrupt ▁line ▁( pin ) ▁which ▁it ▁as ser ts ▁when ▁it ▁wants ▁to ▁signal ▁an ▁interrupt ▁to ▁the ▁host ▁processing ▁environment . ▁This ▁traditional ▁form ▁of ▁interrupt ▁sign alling ▁is ▁an ▁out - of - band ▁form ▁of ▁control ▁sign alling ▁since ▁it ▁uses ▁a ▁dedicated ▁path ▁to ▁send ▁such ▁control ▁information , ▁separately ▁from ▁the ▁main ▁data ▁path . ▁ ▁M SI ▁rep laces ▁those ▁dedicated ▁interrupt ▁lines ▁with ▁in - band ▁sign alling , ▁by ▁ex ch anging ▁special ▁messages ▁that ▁indicate ▁interrupt s ▁through ▁the ▁main ▁data ▁path . ▁ ▁In ▁particular , ▁M SI ▁allows ▁the ▁device ▁to ▁write ▁a ▁small ▁amount ▁of ▁interrupt - des cri bing ▁data ▁to ▁a ▁special ▁memory - ma pped ▁I / O ▁address , ▁and ▁the ▁ch ips et ▁then ▁del ivers ▁the ▁corresponding ▁interrupt ▁to ▁a ▁processor . ▁ ▁A ▁common ▁mis con ception ▁with ▁M SI ▁is ▁that ▁it ▁allows ▁the ▁device ▁to ▁send ▁data ▁to ▁a ▁processor ▁as ▁part ▁of ▁the ▁interrupt . ▁The ▁data ▁that ▁is ▁sent ▁as ▁part ▁of ▁the ▁memory ▁write ▁transaction ▁is ▁used ▁by ▁the ▁ch ips et ▁to ▁determine ▁which ▁interrupt ▁to ▁trigger ▁on ▁which ▁processor ; ▁that ▁data ▁is ▁not ▁available ▁for ▁the ▁device ▁to ▁communicate ▁additional ▁information ▁to ▁the ▁interrupt ▁handler . ▁ ▁As ▁an ▁example