It does need to be done for DASD. It is all handled by CCW prefixing. The prefixed CCW(s) give the control unit the knowledge as to whether to allow the channel program to write data onto tracks or not, and also controls switching from the current track to any other track. Long ago the prefixing CCWs were called Seek and Set File Mask. Then they collapsed into one CCW called Define Extent. Today's prefixing CCW is called Prefix, and it subsumes all the functions performed by Seek, Set File Mask, and Define Extent, and it also enables or disables a host of other newer functions.
Bill Fairchild Programmer Rocket Software 408 Chamberlain Park Lane * Franklin, TN 37069-2526 * USA t: +1.617.614.4503 * e: bfairch...@rocketsoftware.com * w: www.rocketsoftware.com -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of Paul Gilmartin Sent: Wednesday, October 03, 2012 9:36 AM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: How to get a tape's DSCB On Oct 3, 2012, at 08:15, McKown, John wrote: > It would be very difficult and have a lot of overhead to have IOS (not iOS) > check every CCW chain for "suspect" CCWs. ... > Doesn't that need to be done anyway for DASD channel programs? Or is that all handled by CCW prefixing? -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
