Google has 10,000 servers spread in 13 data centers which are located in different places.These data centers are located in US and Ireland.(i.e. Santa Clara, California and Herndon, Virginia in US and Dublin in Ireland.And each data center has its own IP address.Domain names and IP addresses of google’s data centers are listed as :

Domain IP-Adresse

www-ex.google.com 216.239.33.100
www-sj.google.com 216.239.35.100
www-va.google.com 216.239.37.100
www-dc.google.com 216.239.39.100
www-ab.google.com 216.239.51.100
www-in.google.com 216.239.53.100
www-zu.google.com 216.239.55.100
www-cw.google.com 216.239.57.100
www-fi.google.com 216.239.41.100
www-gv.google.com 216.239.59.100
www-kr.google.com 66.102.11.100
www-mc.google.com 66.102.7.100
www-lm.google.com 66.102.9.100

What do you know about search engine robots?
Well,they are data retrieving programs which are also known as “spider” or crawler for what they do.Your websites will be indexed in search engine only when they spiders crawl on your sites.Robots collect links from each page they visit and crawl from one page to other through the links they collected.As they reach your websites,they first check the robot.txt file.This file give the information about the limits upto which the robots can enter to your website.There are many things that robots cannot do.They cannot enter the password protected area,in your websites robots will not understand flash movies,images and javascript,also they cannot click the buttons on your websites.

Summiting a webpage in a search engine means your webpage(url) will be listed in the robots’ queue of website to visit in their next outing for detection.even if you do not summit your url in search engines,robots will reach your webpages through the links which are link to you.So,increasing link popularity is also one of the important factor to get listed in search engine.