Why Are Google Search Results Faster Than Local Hard Drive Queries?

When you search for something using Google, the results are returned in milliseconds, but searching for a file on your own hard drive can take minutes. What gives? Why is a search engine query faster than a local file search?
Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.

The Question

SuperUser reader Arne wants to know why his local search is so slow compared to a search engine query:

When I search a file on my HD in Windows 7 or Windows XP it takes some minutes to finish the process.
If I fill in a search term in Google, the answer is on my screen in milliseconds. How is it possible for Google to search the Internet, that is many times larger than my hard drive, faster than my OS can search my computer.
Is it ‘only’ a matter of computing power and the right algorithm?

He’s certainly not the only one who has noticed the discrepancy; right out of the box with no customization operating-system based search is pretty darn slow.

The Answers

SuperUser contributor Simon highlights the fundamental difference between a Google search query and a non-indexed Windows search:

Google is not searching the internet: it is searching an index. Google has huge server farms which are constantly scanning and indexing the internet. This process takes a lot of time, just like the search of your unindexed hard drive. In Windows 7, there is an option to index your hard drives. This process takes some time at first but once it is up and running the results of a search will be instantaneous.
If you want to know more about how the Google search works you can read Google’s article “How Search Works” or read the article “How Stuff Works: How Google Works“.