How often does PR change?

I know the basics about Pagerank, but I'm confused about how and when it changes. Does Google update all websites' Pagerank in one giant update, or does each website have it's own schedule for Pagerank updates?

How often does the PR update normally take place?

Thanks.

 

Tool bar happens once every three months. However, Google uses real PR value for the SERP computation.

 

google usually updates page rank 4 times in year the last one was 2 weeks before. it's time to wait for 3 months more

 

3 to 4 months after the update

 

Where is this come from? Maybe they don't use PR for results at all?

 

mabbe 6 mths too ! heh

 

approx each and every 3 months google update the PR.

 

Thanks everyone for your replies.

So, Google is constantly updating the PR, but the toolbar is only updated every 3 months?

When Google performs an update, do they often change the algorithm?

 

These information is available in Matt Cutts blog and Google webmaster guide.

PR is included in the rankings of web pages:
http://www.google.com/technology/

 

Ok, just 'real PR' puts me in a confusion - some people talks like there were a second Pagerank used for position computing. But with this I agree.

 

google usually updates page rank 3-5 times in year