>Is there a bit setting in the CVT or another control block structure >that indicates the presence of DATA SPACE Services is available ?
Data space services have been available since MVS/ESA SP3.1.0. They need not be "checked for". Bit CVTH3310 / CVTESA (the same bit) which was introduced in that release will be on in all releases. >it is suggested that the developer obtain an additional 4K Block >when reserving Data Space storage. This is because some Systems >return an Origin address at 4096 and Not 0. >. >In other words the processor does not support an Origin of 0. >From a programming/coding perspective, can this be detected ? >. >How does the System indicate this to a programmer before the >DSPSERV macro is issued ? It is not a necessary conclusion that "some systems return an origin address at 4096" is analogous to "the processor does not support an origin of 0". Imagine a system option that said not to return origin 0 even if the processor supported it (this is an option we have considered). But it does happen that all supported processors do support an origin of 0; nevertheless a program generally should not rely on that. The system does not provide any indication of whether page 0 would be returned (of course the returned "origin" will indicate if it was returned) FWIW, use of HIDEZERO=YES on DSPSERV (introduced in z/OS 2.1) is highly recommended (you would then intentionally not use page 0 even when it is returned) in order better to detect program errors of using uninitialized-but-0 pointers. Prior to z/OS 2.1 there was an alternate technique to making things "blow up" on a reference to the 0 page. A normal protocol (for example) to obtain a 2G data space is to request the maximum allowed number of pages, and accept either RC=0 or RC=4. Peter Relson z/OS Core Technology Design ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
