From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of John McKown Sent: Thursday, March 26, 2009 2:53 PM To: [email protected] Subject: "A foolish consistancy" or "3390 cyl/track architecture"
>I just had a Webinar with Dino software on z/OS 1.10 and ICF catalogs. Very interesting. The most interesting thing to me was how IBM implemented Extended Address Volumes. There is a 4 byte area in the CCW. Historically this is the CCCCHHHH (in nybbles) field. What IBM has done is take the high order 3 nybbles of the HHHH and made it part of the cylinder address, but although physically after the historical cylinder address, it is logically the first 3 nybbles of the cylinder address. I.e. C0C1C2C3H0H1H2H3 has become C3C4C5C6C0C1C2H0 (wish I could do subscripts properly). Close, but no cigar. The 4 bytes you mentioned are not in the CCW. They are in the "disk address", aka "Record Identifier", part of the Count Field, which is the first of three possible fields in each CKD record stored on a track. The rest of your EAV discussion was spot on. The two constants of 15 tracks per cylinder and 56KB per track are embedded in gazillions of lines of code inside z/OS and also bazillions of lines of microcode in the DASD controllers/subsystems (and now maybe channels, too). Bill Fairchild Rocket Software ---------------------------------------------------------------------- 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
