PageRank Technology: PageRank reflects our view of the importance of web pages by considering more than 500 million variables and 2 billion terms. Pages that we believe are important pages receive a higher PageRank and are more likely to appear at the top of the search results.
PageRank also considers the importance of each page that casts a vote, as votes from some pages are considered to have greater value, thus giving the linked page greater value. We have always taken a pragmatic approach to help improve search quality and create useful products, and our technology uses the collective intelligence of the web to determine a page's importance.
It's a like a cascading effect. So internal pages will benefit from this too. Pages linked from the home page will also be given more weight and on down the line .
Generally speaking a new website might get a PR1 or PR2 after some time, a PR10 is the pinnacle and there is only a handful of pages in the world that get that distinction like google.com or usa.gov. When I say handful that is exactly what I mean, there might only be 20 of them at the very most. Each successive rank becomes harder to achieve, getting from a PR1 to a PR5 as has been done here although no little achievement wouldn't be like going from PR5 to PR9. A PR9 would be like apple.com so even achieving that would be impossible for most sites
Only Google would know the exact measurement used but each rank increase is significantly harder to achieve. The PR values would actually equate to something like this.
PR1 = 1
PR2 = 10
PR3 = 100
PR4 = 1000
PR5 = 10000
PR6 = 100000