Originally posted by: taltamir
Maybe it is marketing, maybe there is some cost we are not aware of (board production cost maybe? power consumption?)
wait... power consumption... isn't QPI more power hungry?
Power consumption is definite advantage for DMI vs. QPI, but that isn't enough of an advantage in mainstream desktop.
DMI should be cheaper as its really a dedicated PCI Express x4 port and PCI Express is already on the chipset, while QPI is a brand-new high bandwidth interface. It might also require more routing lines for QPI than DMI which would reduce board costs.
I also like to quote an article first written when Nehalem came out:
http://www.realworldtech.com/p...icleID=RWT040208182719
"Nehalem differs from the previous generation in that it was explicitly designed not only to scale across all the different product lines,
but to be optimized for all the different product segments, from mobile to MP server. This implies a level of flexibility above and beyond the Core 2."
See, Bloomfield and Tylersburg(Core i7 and X58 chipset), is really a Gainstown and its partner chipset that had MP capabilities and ECC taken out. As mostly a 2P server platform, flexibility like 2x16 PCI Express 2.0 lanes and triple channel memory are probably more important over things like DMI and 2 chip configuration.
The
current Core i7 only has 1% of Intel's sales, which is miserable. The Core 2 Quads have around 10% market share which means Core i7 isn't doing its job as its "successor" and its really up to Lynnfield to do it.
The rest of the users don't care about SLI/Crossfire and debatable advantages that tri channel brings over dual channel in PC setups. 2 chip configuration, lower power, possibly better single GPU performance with integrated PCI Express controller and cheaper board costs make Lynnfield attractive over Bloomfield with vast majority of the users.
I guess you can conclude the reasons are marketing. But I think they aren't just mere marketing based crippling but a solid reason for more buyers to migrate to the platform. It also provides a "trickle-down" for the cheaper and lower power platforms. Like, you don't want to have QPI on a ULV platform.
Dunno but it'd make more sense to have it integrated, instead of MCM'ed. In an MCM CPU, the core and the GPU need to talk to each other via something.. so that means the core should have either QPI or PCIe built-in anyway. It'd make more sense to have PCIe controller built-in, but as usual I have no source or factual basis.
The original "Havendale" had entire Northbridge on the "other" die. I can't see why it would be different as Clarkdale was a product that was pulled forward. Having PCI Express on the IMC/GPU side would have given flexibility to quickly migrate the 45nm core to 32nm core on the CPU, which might have been not true with integrated PCI Express controller.
Since the memory controller and GPU is already on the "other die", a connection like QPI is needed for communication between the two MCM chips.
