That is the reason that IBM allows installations to set the MEMLIMIT. While it is true that even a reasonable limit can be abused by multiple jobs, you would have the same exposure in a 31 bit world if you allow jobs to use REGION=0M. Wayne Driscoll Product Developer JME Software LLC NOTE: All opinions are strictly my own.
-----Original Message----- From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf Of Veilleux, Jon L Sent: Tuesday, July 18, 2006 6:26 AM To: [email protected] Subject: Re: 64-bits is a really big number! - was z/OS level for SETFRR for AMODE(64) I always get blank looks when I ask what would happen if someone actually tried to exploit 64bit addressing to the fullest. How do we provide page space to back these requests? As someone responsible for keeping our mainframes up and running, it worries me that application type people have the ability to crash the system just by a stupid mistake. One STORAGE loop in a 64bit address space and the paging subsystem is toast. I know that there are other exposures that application folks can use to crash the system, but, to me, this looks like an accident waiting to happen. Jon L. Veilleux [EMAIL PROTECTED] (860) 636-2683 -----Original Message----- From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf Of Craddock, Chris Sent: Tuesday, July 18, 2006 1:05 AM To: [email protected] Subject: 64-bits is a really big number! - was z/OS level for SETFRR for AMODE(64) > >> AFAIK, the total capacity of all DASD ever manufactured is still > >> insufficient to fully back even ONE 64-bit address space.... > > At the rate 80 - 200 gigabyte drives and higher have been produced and > sold, is the statement being made for only mainframe DASD? I realize > that no z box could handle that much DASD space and wonder if either i > or p boxes could in theory. Nothing could. Let's make a few simplifying assumptions to make the math easy. First let's use 256GiB as the drive size. Yeah, that is way bigger than any MF drive ever shipped, or ever thought of, but it's about the size of the drive in my PC and you can buy bigger drives now for a few hundred bucks. <snicker> Anyway, one of those puppies is (2**8)*(2**30) = 2**38 bytes And a single 64-bit address space is, well 2**64 bytes. So assuming you could use the whole drive, the number of these current generation drives that you would need to back a single address space is (2**64)/(2**38) = 2**(64-38) = 2**26 = 67,108,864 Ok, so on that basis I was a little pessimistic about the time we would need to build enough disk to back one address space. It is becoming plausible that some time in the relatively near future there will be enough disk storage capacity on Earth to map a single 64-bit address space. Of course, housing, powering, wiring, configuring, initializing and addressing that much disk storage would be somewhat of a problem and doing it all over again to map that second address space will be a real b1tch! In other words, 2**64 is a phenomenally large number. In terms of actual usable storage, it is wildly beyond the limits of our current technology and certainly beyond my feeble imagination about what one might actually fill it up with. An RFID for every star and galaxy perhaps? Endless re-runs of "I Love Lucy" in HD? Hell if I know. And for a real giggle-fest, take a look through your own JCL libraries and see how many jobs are still running with "REGION=something_really_small". I am glad that the wizards have made it all work out, but in terms of functional needs, 64-bit addressing is overkill on a cosmic scale. CC ---------------------------------------------------------------------- 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 ----------------------------------------- This e-mail may contain confidential or privileged information. If you think you have received this e-mail in error, please advise the sender by reply e-mail and then delete this e-mail immediately. Thank you. Aetna ---------------------------------------------------------------------- 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 ---------------------------------------------------------------------- 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
