Correct me if I am wrong. I don't pretend to be an expert on this subject. I think of SVCs as hailing from the era of centralized monolithic operating system construction. I would guess that IBM had an "SVC number committee" and they sat down and said "SVC 1 shall do this; SVC 2 shall do that; and so forth." Yes, you can add a user SVC, but fundamentally the SVC has a fixed architecture of 256 possibilities, requiring some sort of central administration. Chris and I cannot both add an SVC 201 to our customers' computers. (Yes, having the number in a config file would be a workaround.)
PCs are inherently much more decentralized. There can be a nearly unlimited number of PCs. Chris and I can both add a PC to our customers' computers without much fear of a collision. And yes, not to disagree with what Chris says, the architecture of SVC is more suited to a single address space, or at least an addressing scheme in which all "privileged services" are at least partially resident in common address space. Charles -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of Christopher Y. Blaicher Sent: Wednesday, August 28, 2019 9:48 AM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: Assembler :- PC Instruction Never measured SVC vs PC. While in some cases PC and SVC are similar, in many ways PC is far superior to SVC. It can be local or globally defined and it can be dynamically defined and removed. (OK, so can an SVC be added and deleted, but I think PC's are easier). Also, an SVC can't do space switching. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
