In a message dated 3/8/2007 9:42:12 P.M. Central Standard Time, [EMAIL PROTECTED] writes: >In my book, that's not *really* a self-modifying channel program. (It's just using the same data area in more than one CCW. I know of at least one ISV product in use today that writes from a buffer and later in that same channel program, uses the same buffer for input.) I agree. To me, a self-modifying channel program is one that alters any part of any of its CCWs, any control fields that they references (e.g., locate record's 16 parameter bytes), or any indirect address list used by any of its CCWs. >The closest thing I've seen to that in MVS are specialized drivers that use PCIs to monitor the progress of a channel program and then maybe make an on-the-fly change to a CCW depending on some status or item of input data. A good example of this is the chains used by ASM to do page-ins and page-outs. But these do not fit my definition above. They are, rather, channel programs dynamically modified by software during the life of the I/O. Two other exotic aspects of the I/O subsystem that have always intrigued me are (1) the address-limit-checking facility which compares data addresses about to be accessed with a previously supplied value and (2) the channel-subsystem priority. I would imagine that ASM uses the CSS priority byte, but does any other product use this or the address-limit-checking facility? I can easily imagine how VM might use both of these facilities, but what part of MVS uses them? Also did or does any product or component other than ASM use the suspend flag in DASD operations? I've seen the suspend flag used on some non-DASD channel programs. Just curious again. Bill Fairchild Plainfield, IL
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