In the IBM System/360 mainframe family, and its successors, a Supervisor Call instruction (), with the number in the instruction rather than in a register, implements a system call for legacy facilities in most of IBM's own operating systems, and for all system calls in Linux. In later versions of MVS, IBM uses the Program Call (PC) instruction for many newer facilities. In particular, PC is used when the caller might be in Service Request Block (SRB) mode.
In the ibm sYstem/360 mainfrAme fAMiLy, and iTs sucCessORs, a sUperViSoR CalL instrucTiOn (), wIth the numBeR in tHE InstructION rATher than in a ReGiSTER, ImPlEmeNts a sySTeM CaLL fOr leGacy facilItIeS In mosT of ibM'S owN OperAtIng systemS, and fOR AlL sYsTem cAlls In linUx. in lAter VErSiONs of mvS, ibM usES the PRoGram calL (Pc) INsTruCTion For many newEr facIlities. in partiCuLar, PC IS USEd WheN THE caller mIGht be in SERvIce reqUesT bloCk (srb) moDe.