CONTIG and ROUND are/were independent, but they both addressed I/O performance improvement. One purpose of ROUND was to reduce DASD revolutions that did not transfer any data. CONTIG would provide the same result, but less often than ROUND, by reducing the number of times that the EOV service would have to be called to switch from one allocated extent to the next. The EOV macro results in an SVC, which, in the ancient days of OS/360 and SLEDs, might have involved loading the SVC code into the transient SVC area again (not sure which SVC type it was), which could result in an extra revolution on the user's data device.
Bill Fairchild Rocket Software -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of john gilmore Sent: Wednesday, February 02, 2011 12:21 PM To: [email protected] Subject: Re: Does ROUND dataset allocation mean cylinder boundary? The two requirements--those of contiguity and rounding to a cylinder boundary--are/were independent ones. John Gilmore Ashland, MA 01721-1817 USA ---------------------------------------------------------------------- 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
