[email protected] (Gerhard Postpischil) writes: > I think you misread his message, which started with command > chaining. But I would be interested in which control units and > controllers allow data chaining beyond 65KiB.
re: http://www.garlic.com/~lynn/2013o.html#6 hexadecimal note a lot of original data chaining was for non-contiguous storage transfers (scatter/gather). cp67 doing emulated i/o had to use it for shadow ccws involving (non-contiguous) page crossing. channel architecture proscribes that ccws aren't prefetched (executed serially one at a time, even datachaining) ... and their could be timing difficulties with cp67 emulated i/o ... when the native (non-datachained) i/o ran find. the issue of page non-contigious i/o was addressed in 370 with IDALs ... where IDAL channel architecture allowed the the addresses to be pre-fetched. IDALs was also used later as part of hack adding more than 16mbytes to 3033 ... even tho instructions and CCWs couldn't address more than 16mbytes. note that many of the i/o devices are now industry standard with IBM legacy controllers and devices (like CKD) purely a simulated artifact. They aren't restricted to record lengths imposed by IBM's legacy CCW architecture. -- virtualization experience starting Jan1968, online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
