> >And in my opinion, that's why DREF is superior to FIXED: it's backed up > >by real frames only when you access it for the first time (like > pageable > >area). And MVS has special facility to make it suitable for disabled > user. > > DREF was introduced when real storage still was a scarce resource but > when > systems already had quite some expanded storage. DREF storage was > pageable > storage but it could only be paged to expanded storage and never to > aux storage.
Not exactly. You should think of DREF as a variety of SQA/ESQA. DREF is like pageable storage only in that it is not backed until it is first-referenced and, if you're prepared to risk handling a S03C abend, that first reference can even occur while you're disabled. The abend only occurs if RSM is unable to find a free frame to assign. Once a frame has been assigned to a DREF area it is effectively the same as an ESQA frame (if it is in a common area subpool) or an ELSQA frame. ESQA is permanently mapped until it is freed or released. ELSQA is private storage, so in swappable address spaces it can be paged out and relocated across a swap cycle, but in practice it probably is indistinguishable from ESQA. Back when there was ESTORE, in-use DREF frames could be stolen and moved to ESTORE. Now that option is gone. However, DREF is still extremely useful because of its deferred backing. 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
