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3. The work of the search engine is divided into three stages, i.e. crawling,
indexing and retrieval
1) Crawling
The search engines have the web crawler or spiders to perform
crawling. The task of crawler is to visit a web page, read it and follow
the links to other web pages of the site. Each time the crawler visits a
webpage it makes a copy of the page and adds its URL to the index.
After adding the URL it regularly visits the sites like every month or
two to look for updates or changes.

4. 2) Indexing
In this stage, the crawler creates the index of the search engine. The
index is like a huge book which contains a copy of each web page
found by the crawler. If any webpage changes the crawler updates
the book with new content.
So, the index comprises URL of different webpages visited by the
crawler and contains the information collected by the crawler. This
information is used by search engines to provide the relevant
answers to users for their queries. If a page is not added to the
index it will not be available to the users.

5. 3) Retrieval
This is the final stage in which the search engine provides the most
useful and relevant answers in a particular order. Search engines use
algorithms to improve the search results so that only genuine
information could reach to the users, e.g. PageRank is a popular
algorithm used by search engines. It shifts through the pages
recorded in the index and shows those webpages on the first page of
results that it thinks are the best.

6. In the beginning, in 90's, search engines was not as effective as it is
today; it was mainly focused on keyword matching and backlinks. So,
it was quite easy for the low-quality websites to rank higher by
targeting their exact keywords with lots of backlinks.

7. 2003 Updates
Florida
It was introduced on 16 November, 2003. It brought significant change to
Google's algorithm and put an end to the use of keyword stuffing to
manipulate search engine results
Fritz
It was introduced in July 2013. With this update Google changed its way
of updating the index; now instead of indexing on a monthly basis, it
started indexing on daily basis.

8. 2004 Updates
Brandy
This update was launched in February 2004. It expanded Google?s index
and incorporated Latent Semantic Indexing (LSI) which enabled
Google to better understand synonyms.
Austin
It was introduced on 23rd January 2004. This update was actually some
improvements in the Florida update. It targeted the on-page spam
tactics like invisible text and meta-tag stuffing

9. 2005 Updates
Bigdaddy
It was rolled out in December 2005. It was an infrastructure change that
brought new technicalities related to URL canonicalization, redirects,
etc. It helped Google to prepare for future developments

10. 2007 Updates
Buffy
It was introduced in June 2007. This update was named in honor of
Google's Vanessa Fox. Matt Cutts said that it was just some minor
changes like the integration of search results with news, images and
videos, etc.

11. 2009 Updates
Caffeine (Preview)
In August 2009, Google released Caffeine (Preview); the upcoming
infrastructure change to improve and integrate indexing, crawling and
range of their search engine index.
Vince
It was introduced in February 2009. It was seen as a big change that would
favor big brands but Google?s Matt Cutts cleared that it was a minor
change focused on ranking signals like trust and authority.

12. 2010 Updates
Caffeine
In June 2010, Google updated its caffeine algorithm to introduce new web
indexing system. It helped Google to improve the speed of search
engine and integrated crawling and indexing that resulted in a fifty
percent fresher index.

13. 2011 Updates
Panda/Farmer
It was first launched on Feb24 2011. This algorithm was used to assign a
score to webpages based on the quality of the content and de-rank the
sites with low-quality content. Its job was to identify and de-rank
content farms, sites offering thin content or sites with high ad-to-
content ratio.

14. 2012 Updates
Penguin
It was introduced on 24th April 2012 to target the sites that were
spamming the search results by buying links or using some other link
networks designed specifically to boost rankings. Google issued
warnings through Webmaster tools and penalized the sites for not
following its guidelines.

15. 2013 Updates
Hummingbird 1.0
It was introduced by Google on 20 August 2013 to better understand
the changing face of the Web. It was capable of understanding the
intent of long search terms instead of just recognizing specific
keyword. It helped Google recognize long-tail search terms and
accurately rank answers to such long-tail keywords. It enabled users to
ask questions and get appropriate answers.

16. 2014 Updates
Penguin 3.0
It was introducedon 17 October 2014. It was just a refresh that helped those
websites boost their ranking who were de-ranked in the previous update
(Penguin 2.1).
Panda 4.1
It was the 27th version of Panda released by Google on 23 September 2014.
Google said that it will help search engine identify poor content so that
small or medium sized websites with quality content could rank better.

17. 2014 Updates
Pigeon
It was rolled out in July 2014, for local businesses. Google said that it will
create closer ties between local and core algorithms so that people
could find useful and accurate information in local search results.
Panda 4.0
This Panda update was introduced on 19 May 2014, to help small websites
and businesses with limited resources. It was a change a data refresh; a
change in Panda algorithm.

18. 2015 Updates
Panda 4.2
On 17 July 2015, Google rolled out Panda refresh (Panda 4.2). It has no
immediate effect on rankings. According to Google, it impacted 2?3 %
of English language search queries.
Mobile-Friendly Update (Mobilegeddon)
It was rolled out on 21 April, 2015. It made mobile-friendliness an
important ranking factor for mobile searches. Its job was to boost the
rankings of mobile-ready pages so that quality and relevant content
could be provided to mobile users.

19. 2016 Updates
Penguin 4.0
Penguin 4.0 was announced on September 23, 2016, with few changes
like it will be part of core algorithm, will update in real time and will
be page specific instead of affecting the entire domain.
Mobile Friendly Boost Update
It was launched in May 12, 2016, to help mobile-friendly sites on mobile
search.