[assuming latest greatest CS6 and system, okay well maybe one limited to 4GB RAM]
Well if you have a Nested whatever [720p 30fps] previewed (generic and standardized in my example from png sequence), and apply various effect layers (auto contrast, auto levels, alias, sharpen, dark/shadow, and hey maybe I want more as a basic start for image enhancement), well it's apparently a lot of processing that needs to be done agreed (Cuda/GPU? please).
Anyway here's the observation for the dev team to ponder.
On Win7 looking at the process resource monitor for commit memory, it seems to be leaking out of control so it's no wonder you run out of RAM and it says "Close some programs".
Delete all your effects!? seriously though.
You can slice the Nested piece into many (and I mean many) pieces and preview each one to get your green bar. [possible needing various saves and restarts of the application]
Alternatively you can for the system [requires reboot] set a manual paging to astronomical values to handle the massive memory leak.
Any other suggestions I'm missing here?
Okay so really the situation programmatically speaking it seems to me is each frame gets processed and then that frames ram is reusable or should be freed after writing to disk. Maybe if you have contiguous clips in should be broken into pieces when paging begins. Clearly this is not being handled properly and it's pretty obvious... to me.
Thank you for your prompt attention to this issue, otherwise my apologies for expressing my observations so clearly.
Frankly the whole idea of the green bar working in large pieces seems off to me. It's good to know when those parts need rebuilding but it's not write to suck up RAM until the last bytes computed and still not release it for the next preview or other applications on the system.
And as always thanks for listen and taking seriously all user feedback.
Thank you for your prompt attention to this issue
Pffft! Adobe doesn't do anything 'promptly'. You're much better off just upgrading to 12 or 16 GB RAM.