Loading file multiple times

When I load a certain MAT file twice (different runs of the script) its look like the reading is much faster in the second time (unless i've load a lot of other files between the runs). Why is it hapenning and how can I make it happen always? (even when I'm loading a lot of other files between)

examples: Reading 12MB file (compressed, v7.3 I think)

first run - 0.3 sec

second run - 0.15 sec

Reading 26MB files (non - compressed, v6) % same data as above but in v6 now

first run - 0.85 sec

second run - 0.03 sec % !!!

It's look like the file is in the memory in some way.

Thanks

Noam