Santa Rose In-Depth

CPU

Intel suggests using dual-core processors on Core micro-architecture in contemporary notebooks. They are known under Merom codename however, their internal design is very similar to that of regular desktop Conroe CPUs. It seems quite logical if we recall that Core micro-architecture comes from the mobile Pentium M processor family. As a result, Intel engineers take advantage of the fact that by limiting the clock frequencies of Core 2 processors they can provide heat dissipation and power consumption acceptable for mobile platforms.

Note that Merom (mobile Core 2 Duo) have arrived into notebooks a while ago, even before Santa Rosa platform appeared. They became the basis for Centrino Duo when the previous generation Napa Refresh platform came out. Nevertheless, the new Core 2 Duo notebook processors are still different from their predecessors. However, the differences are purely cosmetic ones. Core 2 Duo of the Santa Rosa platform acquired 800MHz bus support, while the previous platform worked with 667MHz Quad Pumped Bus.

So, the bandwidth of the bus between the processor and the chipset increased to 6.4GB/s. of course, this is quite far from the potential of the 1600MHz bus that Intel intends to employ in server and high-performance workstation environment in the nearest future, but we shouldn’t underestimate the importance of this change. The processor bus bandwidth is currently falling far behind the memory bus bandwidth. Therefore, any increase in the FSB speed will improve the performance tremendously in those applications that are sensitive to the memory subsystem performance.

Besides the higher bus frequency, the new mobile platform acquired a slightly modified Socket P processor socket with 478 pins. As a result of this innovation contemporary notebooks should be compatible on the hardware level with the upcoming 45nm Penryn processors that are scheduled to start entering the mobile segment in early 2008.

Core 2 Duo with 800MHz system bus was not the only type of processors to appear in the mobile market. They also introduced Core 2 Extreme processors. Just like in the desktop segment these dual-core CPUs offer higher performance, which in this case results from higher clock speed. However, Intel has to sacrifice some of the heat dissipation to hit higher clock speeds: mobile Core 2 Extreme processors exceed the sacred 25W here.

The complete list of processor models for Centrino Duo (Santa Rosa) platform is given in the table below:

Core 2 Duo and Core 2 Extreme processors intended for the refreshed Centrino Duo platform now boast one more interesting feature aimed at improving the system performance in single-threaded applications even more. This technology is called Intel Dynamic Acceleration.

This technology implies that under high workload the processor clock frequency increases only on one of the cores while the other one is idle (only one of the processor cores gets overclocked). To be more exact, during single-threaded applications processing the CPU frequency increases by 200MHz above the nominal value because the processor clock frequency multiplier automatically increases by 1. Since the workload is single-threaded the processor heat dissipation and power consumption are guaranteed not to exceed the acceptable limits.

By the way, Core 2 Duo with 800MHz bus also acquired some new power-saving technologies. CPUs learned to hibernate even deeper, a state called Enhanced Deeper Sleep. Moreover, they also allow to dynamically manage the FSB bus frequency that can be dropped down in low-activity modes. As a result, new faster processors are not any less economical than their predecessors and hence outperform them from the performance-per-watt prospective.