The file is only being read once according to the blog and then it is in memory. This isn't an I/O intensive application at all.

I have written a small script in python that does something similar. I have a word list with 1000 words and I check the presence of the words. Here is the thing. For every word I go through the entire file. So lets say I scan the file one thousand times. In fact I did something more complicated and ended up going 6000 times over the original file and yet it still took only three seconds. If all these scans had to reread the file it would take forever.