> -----Original Message----- > From: IBM Mainframe Discussion List > [mailto:[EMAIL PROTECTED] On Behalf Of Edward Jaffe > Sent: Thursday, December 21, 2006 3:07 PM > To: IBM-MAIN@BAMA.UA.EDU > Subject: Re: Question about SVC 109 > > > Lindy Mayfield wrote: > > The doc above says specifically: > > ESR (type 4) SVC - is type 2 > > > > But I didn't quite understand that. Seems SVC 109 is a > type-2 that only calls type-4 SVC's, but that doesn't quit > jive for me (yet). That was my question. (-: > > > > SVC 109 is a type-2 standard SVC routine that performs routing for > type-3 or type-4 extended SVC routines. > > -- > Edward E Jaffe
And just to confuse things futher, I cannot see any significant difference between a type 2, type 3, or type 4 SVC. In the past, a type 3 SVC was dynamically loaded from SVCLIB into a transient area (I think that's what it was called). This area was fixed in size, so a type 3 could not be larger than that (4K?). If you had an SVC which needed to be larger, you created a type 4 SVC. The only difference between a type 3 and a type 4 was that a type 4 could do an XCTL to another "segment" of itself (an independant module in SVCLIB). This was a sort of dynamic overlay structure. Today, a type 3 can be as large as you need, so I see absolute NO need for a type 4 any more. In fact, the type 3 should be more efficient because it would not do the XCTL. Both are LPA resident, so that is the same. A type 2 SVC is NUCLEUS resident (but can now be loaded as an independant module in SYS1.NUCLEUS). IIRC, the nucleus is still non-pageable (true?). In the past, I remember some SVCs being type 2 so that they could modify themselves (like do a GETMAIN on the very first call, and save the address in the SVC's "data" area). As far as I can see, in today's z/OS environment, everything could be architected as a type 1, 3, or 6 SVC with no real impact on functionality. If I'm blowing smoke, please educate me on the advantages of a type 2 (other than no paging, I guess) or a type 4. -- John McKown Senior Systems Programmer HealthMarkets Keeping the Promise of Affordable Coverage Administrative Services Group Information Technology The information contained in this e-mail message may be privileged and/or confidential. It is for intended addressee(s) only. If you are not the intended recipient, you are hereby notified that any disclosure, reproduction, distribution or other use of this communication is strictly prohibited and could, in certain circumstances, be a criminal offense. If you have received this e-mail in error, please notify the sender by reply and delete this message without copying or disclosing it. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
