Steps to reproduce: Open a dvi file in Yap and wait for the file to be completely rendered. Open File Monitor (from www.sysinternals.com) and set the filter to Yap. Wait 10 seconds, count the number of times Yap opened the file.
My results were between 400 and 7500 times per second! It doesn't matter whether you change pages or leave the file alone in the background. The only way the count would go down to about 10 times per second is to minimize the window.
I expect that Yap would stop trying to read the file in the disk after it finished rendering.
Could anybody post their measurements here for comparison?
In the attached screenshot, the cycle of opening the dvi file, reading info (not data), and closing the file is shown. My guess is that Yap wants to be sure that it has the latest version of the dvi file.