I bought a PB in the middle of auguest, and upgraded to 756 right away. now I bought a 512 chip to add. meaning it came with 256. I looked at apple.com a while ago and noticed that the pb's were shipping with 512 std. when did that little upgrade take place?

They did a mid-life upgrade Jan 31 2005 where they started shipping with 512 Mb RAM.. HOWEVER in the 12" model this was (and still is) 256 Mb built in memory and a 256 Mb module in the one and only socket, so when you installed the 512 chip to bring it to 768, you effectively threw away half of the "512" it came with.

And that is the case with the current 12" as well.

Thanks
Trevor
CanadaRAM.com