On 9 December 2013 18:04, DASDBILL2 <dasdbi...@comcast.net> wrote: > My phrase "billions of CCWs" was assuming you already knew how to read a full > track with only one CCW. A fully > populated EAV can have 16 to the 7th power cylinders and each cylinder can > have 15 tracks. One Read Track CCW > (and not Read Multiple CKD, which is too primitive) per track would require 4 > 026 531 840 CCWs, which is four billion, > which is "billions". And each CCW would need 56K bytes of real, fixed > storage for the life of this I/O request. That's > 228 terabytes of real storage, which is the main reason why I called this > channel program theoretical.
In the real world, PCI would be used to modify the channel program on the fly. It would presumably be copying the data to another device (tape or disk), and as long as that output device could keep up, there's no reason for this to be a theoretical-only scheme. Much the same thing, on a smaller and slower scale (though perhaps not much smaller relative to the hardware of the day) was done by APL\360 with its terminal I/O. The terminal read channel program was unending, with new buffers being chained in based on PCI interrupts. Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
