> And it could already be untrue previously e.g. the Pentium D were rushed out by sticking two P4 dies on the same PCB, I think they even had to go through the northbridge to communicate
Part of me hopes you're wrong here. That is absolutely absurd.
But Intel got caught completely unaware by the switch to multi-core, just as it had by the 64b switch.
The eventual Core 2 was not ready yet (Intel even had to bridge to it with the intermediate Core, which really had more to do with the Pentium M than with the Core 2 though it did feature a proper dual-core design... so much so that the Core solo was actually a binned Duo with one core disabled).
So anyway Intel was caught with its pants around its ankle for the second time and they couldn't let that happen. And they actually beat AMD to market, having turned out a working dual-core design in the time between AMD's announcement of the dual-core opteron (and strong hints of x2) and the actual release, about 8 months.
To manage that Intel could not rearchitecture their chip (and probably didn't want to as it'd become clear Netburst was a dead-end), so they stapled two Prescott cores together, FSB included, and connected both to the northbridge.
It probably took more time to validate that solution for the server market, which is why where AMD released the dual core Opterons in April and Athlons in May, it took until October for the first dual-core Xeon to be available.
"The Pentium D brand refers to two series of desktop dual-core 64-bit x86-64 microprocessors with the NetBurst microarchitecture, which is the dual-core variant of Pentium 4 "Prescott" manufactured by Intel. Each CPU comprised two dies, each containing a single core, residing next to each other on a multi-chip module package."
They didn't have to go through the northbridge itself, but they had to go over the frontside bus that connects the CPU to the northbridge (and would normally be point to point).
Part of me hopes you're wrong here. That is absolutely absurd.