diamonddriller

As a further, I have experienced a remarkable recovery. The iMac went to sleep with the stuttering XP running, and when I returned to wake things up 10 minutes later, XP was still running (of course) but the frame rate was fantastic, and there was not a stutter to be seen........ I have shut down XP and restarted it, upped the resolution, etc., and it seems OK so far. As for later, or tomorrow, who knows?

There are several of us iMac users, particularly with mid 2011, 27" , 16Gb ram and ATI Radeon 2Mb graphics cards, who are now getting stuttering and varying frame rates under Yosemite (even 10.10.1). These faults are making XP unusable. I'm praying for a resolution to this soon, and am having to use a Boot Camp installation while I wait, as well as (and it's slow...) booting from an external HD with Mavericks on it, and then using my internal HD's X-Plane installation. Not good