cs files compatible with cs3

[woof75]

I think that I have some old files saved in cs have been slowing my computer down in cs3. I had an old file that took 12 seconds to open and I saved it as a different filename and didnt change the file and it opens in 2 seconds whilst the old one still takes 12. The only thing I can think of is the old file may have been made in CS, is that possibly what could cause it to be so slow?