> I wonder what the significance of being interruptible is if not garbling results.
MVCL came along with System/370 - at that time uniprocessors were more common and a lot of IBM hardware had strict timing considerations - 1419 interrupts HAD to be handled within so many milliseconds or you "lost" the document - sometimes literally. So an instruction with a potentially long duration HAD to be interruptible for I/O interrupts to be handled in time. I'm not sure what the current situation actually is - the time-critical peripherals have gone and most systems are multi-CPU with the SAP offloading a lot of I/O processing. I doubt that MCVLs get interrupted much these days. > I imagined that MVC was "atomic" in nature meaning that the second processor couldn't "garble" things until the MVC had run it's course. I think that's "implementation-dependent", as IBM would say. Unwise to rely on it. -- Phil Payne http://www.isham-research.com +44 7785 302 803
