Perhaps there is more to the emulation of CKD than the thread touches on. Disk Drives stopped recording in CYLS some time ago because the time for head switching is greater than the minimum seek time. Drives today record in a serpentine method across the platters, doing a switch-back (best word I can think of) to the next head at intervals defined by the HDD designers.
The whole idea of tracks and CYLS is really dead and buried as far as the real hardware is concerned. Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of > Paul Gilmartin > Sent: Friday, March 27, 2009 2:01 PM > To: [email protected] > Subject: Re: [IBM-MAIN] "A foolish consistancy" or "3390 cyl/track > architecture" > > On Fri, 27 Mar 2009 14:41:10 -0500, Chase, John wrote: > >> > >> Well, if IBM's new DASD architecture were manufactured in the same > >> manner as previous DASD devices, you would have 278,921,216 tracks > >> on each surface. What diameter do you think such platters would be? > >> How long would it take the access arm to traverse the radius? > > > >How much power would it take to spin them fast enough to be usable? :-) > > > Long ago, I attended a Preview of XA presentation at which the IBM > presenter (Bill Malleck?) stated that smaller rotational latency > could be achieved only with smaller platters. Mechanical > disruption happens at a surface velocity roughly the speed of > sound -- sqrt( Young's modulus / density ). The problem > engineers were confronting was oxide flying off the substrate. > By analogy, "Have you ever watched the chef making pizza, > throwing the dough in the air to form the crust? Notice that > he only puts the sauce on after." > > Tetrahedral carbon platters? Graphene? (They're working on it.) > > -- gil > > ---------------------------------------------------------------------- > 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
