OOMSYSTEM

What is PageRank?
Page rank is a way of knowing what is the importance of the page for the web. It is generally considered that when one page ranks other it is casting its vote foe that page. more the number of votes the more important the page is. Also the page which is casting the vote is important. The importance of the page is determined by calculating the number of votes. The importance of the votes is determined when page rank is calculated. page rank is an important factor for search engi9nes because it is the only way of calculating page's importance. Page Rank is designated as "PR".

Note:
All links are not important foe Google. For instance, they filter out links from known link farms. Some links can cause a site to be penalized by Google. They rightly figure that webmasters cannot control which sites link to their sites, but they can control which sites they link out to. For this reason, links into a site cannot harm the site, but links from a site can be harmful if they link to penalized sites. So be careful which sites you link to. If a site has PR0, it is usually a penalty, and it would be unwise to link to it.

How is PageRank calculated?
In order to calculate the page rank of a page all the inbound links are taken into account. these are the links that come from other sites to our sites. The mathematical formula to calculate PageRank is:

PR(A) = (1-d) + d(PR(t1)/C(t1) + ... + PR(tn)/C(tn))
Here,
t1-tn is the pages linking to page A.
C is the number of outbound links
d is damping factor (equal;l to 0.85)

The equation can be simplified as:

a page's PageRank = 0.15 + 0.85 * (a "share" of the PageRank of every page that links to it)

"share" = the linking page's PageRank divided by the number of outbound links on the page.

A page "votes" an amount of PageRank onto each page that it links to. The amount of PageRank that it has to vote with is a little less than its own PageRank value (its own value * 0.85). This value is shared equally between all the pages that it links to.

From this, we could conclude that a link from a page with PR4 and 5 outbound links is worth more than a link from a page with PR8 and 100 outbound links. The PageRank of a page that links to yours is important but the number of links on that page is also important. The more links there are on a page, the less PageRank value your page will receive from it.

So one thing which is of great importance is that an inbound link from another site increases our site's PageRank. But be sure that that link is not coming from link farm.

Now lets see how actually page rank is calculated.
Suppose we have 2 pages, A and B, which link to each other, and neither have any other links of any kind. This is what happens:-

Step 1: Calculate page A's PageRank from the value of its inbound links

Page A now has a new PageRank value. The calculation used the value of the inbound link from page B. But page B has an inbound link (from page A) and its new PageRank value hasn't been worked out yet, so page A's new PageRank value is based on inaccurate data and can't be accurate.

Step 2: Calculate page B's PageRank from the value of its inbound links

Page B now has a new PageRank value, but it can't be accurate because the calculation used the new PageRank value of the inbound link from page A, which is inaccurate.

It's a Catch 22 situation. We can't work out A's PageRank until we know B's PageRank, and we can't work out B's PageRank until we know A's PageRank.

Now each time we will calculate the page ranks foe these pages we will arrive at the incorrect result because the new page ranks calculated is also made4 using incorrect values, so the results will always be inaccurate.

This problem can be avoided by doing repeated calculations. Each calculation will produce a more correct value. accurate result can never be achieved but after 40 - 50 iteration we will see very little changes in the result at that time we can say that this is the page rank for a particular page.This is precisely what Google does at each update, and it's the reason why the updates take so long.