What is the difference between Intel T9000 and P8400?

Answer 1

P8400 is a CPU in the P8000 series,

T9000 is a series as well, contains the T9300 for example.

Compare here

http://ark.Intel.com/ProductCollection.aspx?series=35571

and here

http://ark.Intel.com/ProductCollection.aspx?series=33900

It looks like the P8400 is a newer package, has half the cache (a bad thing), and approx 30% less power consumption (good) than T9300, and is cheaper by about 30% too (also good). Finally the T8000 series has a higher front side bus.