1. Search Engines
And how they work

2. How many pages are there on the WWW?
Log onto a computer and try to find out how many web pages there are on the Internet?
Reading them all to find the right ones for your Geography project is clearly not an option! We need an INDEX to search them.

3. Indexing the WWW
But think – Even with a huge team of people, how long would it take them to look at all the pages and make an index? And all those new pages every day? (There’s an extension for you – how many people would need to be in the team for the index to get updated every day?) Its more than the entire population of the UK!

4. So how does Google do it?
Search engines have programs that ‘crawl’ the WWW, looking at the content of web pages, identifying the KEY WORDS and indexing them automatically.
The web crawler programs also look at all of the links between pages.
Pages are ‘RANKED’, so, if I search for ‘rainforest’, google tries to find pages that are most likely to have information about rainforests on them, and puts them at the top of the results.
Pages that are linked to by lots of other pages get ranked higher, because the links are a bit like recommendations.

5. So, if its at the top of the page it’s the most reliable source?
No – it might be a website that has paid to be at the top of the page!
Type Double Glazing into Google. At the top will be sites that have paid to appear if the keywords ‘Double Glazing’ are entered. If someone clicks on the link, Google gets paid! The websites that offer to pay google the most per click, get to the very top
Well, you didn’t think Google did all this for nothing…

6. So how do we know if a website has paid to get to the top?
Well, they are marked as Ad with a little yellow box
Can you see a list of ‘Local’ results? Google looks at your IP ADDRESS and from this can tell which region of the country you are in. It uses this to suggest local companies
If you use an Android phone to do it, it will know EXACTLY where you are. All the time. Unless you have turned off Location Services!

7. Comparing Search Engines
Google overview
Technical how search engines work
Simple how search engines work: Bytesize
Type Mars into the following search engines. Open ‘WS2 Search Engines’ and answer the first question: