Hello, GROUP I spent the whole day reviewing my understanding about the concept of virtual storage and found something I cannot figure out. I hope experts here can give me some hints.
Maybe I should start from GETMAIN. I have used GETMAIN/FREEMAIN for some time in my programming exercises and one question has remained on my mind from the first day I knew these services: After a successful GETMAIN request, I will get a virtual storage area to use. Is that area supported by either real storage or auxiliary storage as soon as the GETMAIN completes? My guess is: it depends and it's very possible that it is not. I cannot find anything to support my above guess in manuals and it's purely from my deduction: 1. I once read in the list that 'if you GETMAIN a two large area and as soon as you begin to access it, it will cause a heavy usage of auxiliary storage.' 2. There is an example in an assembler language book which is about the usage of PGRLSE: Release the area GETMAINed using PGRLSE and then you can still access it. Suppose my guess is true and now I start to access the area GETMAINed. During the translation process, the hardware will find the corresponding entry in the segment table has SEGMENT-INVALID BIT on and it will signal a SEGMENT-TRANSLATION exception. How will the OS handle it? If the area has been GETMAINed, OS will allocate it in the unit of segment: back it up using either real or auxiliary storage. If not, it will throw the exception to my program and if my program cannot handle it I will get a 0C4 completion code. So GETMAIN/FREEMAIN has no direct relation to virtual storage backing up: when you GETMAIN, it doesn't mean OS will try to back up that area and FREEMAIN doesn't mean that area will be released like what PGRLSE does. I know it's not an easy topic and you cannot expect to grasp it in one day. So forgive me if my understanding is wrong and silly. -- Best Regards, Johnny Luo ---------------------------------------------------------------------- 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
