Clarksfield: Nehalem comes to the notebook
Clarksfield — officially called Core i7 — brings Intel's Nehalem architecture to notebooks. The main features of Nehalem, introduced in November 2008, are an integrated memory controller and hyperthreading.
All Clarksfield chips have four computing cores and can handle eight threads simultaneously thanks to hyperthreading (2 threads per core). To achieve a thermal design power (TDP) of between 45W and 55W, Intel has had to reduce clock speeds significantly. Desktop Nehalems run at between 2.66GHz and 3.33GHz, while their notebook counterparts can only manage 1.6GHz to 2GHz.
However, clock speed in this case is less significant than at first sight. Like their desktop equivalents, the mobile Core i7 CPUs have Turbo Boost technology. Temperature permitting, the processor can overclock a single core to a specified maximum frequency within its TDP parameters. Furthermore, the maximum extra from Turbo Boost for Nehalem desktop chips is up to 640MHz, whereas Clarksdale chips can get to up to 1.2GHz beyond their usual clock speed.
This extra speed is particularly useful for applications that are not optimised for multithreading. Until now, such applications have run slower on quad-core chips than on dual-cores. Intel aims to use Turbo Boost to remove this problem.
But a few issues remain with Turbo Boost. When, how often and for how long cores are overclocked depends on operating temperatures. So a poorly-cooled notebook will achieve a lower maximum clock speed.
Clarksfield, together with the PM55 chipset (a descendant of the P55 used on the desktop), constitute the Calpella platform. Calpella will not be marketed under the successful Centrino brand that has served the five previous mobile platform generations. Stickers on the new notebooks will only mention Core i7. But Centrino will not disappear entirely: the name will survive in Calpella's wireless LAN module.
Like the desktop chips, Clarksfield is produced using 45nm manufacturing. A switch to 32nm technology is not yet on the cards for these mobile quad-cores. That step takes place only with the next architecture, which is called Sandy Bridge. All 32nm CPUs with the Nehalem architecture are part of the Westmere family.