Core 2 Duo Updates
Santa Rosa: Core 2 Duo and More
With Santa Rosa, Intel will be moving on to an updated Core 2 Duo processor that supports the new 800MHz FSB design and will actually be switching to a new socket tentatively called Socket P. Socket P is a 478-pin mPGA socket with a different pin layout. The main significance of this is that Santa Rosa will no longer be backward compatible with the Napa designs or with the previous generation Core Duo and Core 2 Duo processors, and Socket P will move forward to support the upcoming 45nm Penryn processors.
Things get a little more complicated from here onwards. Firstly, the Santa Rosa Core 2 Duo will still carry the Merom codename, which to us, reflects that the processor isn't fundamentally different from first generation Core 2 Duos. Indeed, the technical specifications of the Core 2 Duo on Santa Rosa is identical to that of the original Merom, and comes with 4MB L2 cache. However, from what Intel has shown us, the new Santa Rosa Core 2 Duo CPUs have some very clever engineering built-in that are not available on the original Core 2 Duo processors. Without making changes to the processor architecture itself, Intel adds four new 'features' to the Santa Rosa Core 2 Duo chip. These include an 800MHz FSB support, dynamic FSB switching, a more efficient Enhanced Intel Deeper Sleep mode and Intel Dynamic Acceleration.
Dynamic FSB Switching
One of the more anticipated features of Santa Rosa was its FSB boost to 800MHz, thus increasing the overall CPU to system bandwidth by giving the Core 2 Duo much more 'room to stretch'. However, while we consumers are clamoring for more speed and performance, the good folks at Intel are trying their best to save whatever power they can. Dynamic FSB Switching is perhaps the most straight forward feature found in Santa Rosa. Just like how the Core 2 Duo can dynamically scale processor frequency according to load by tweaking its multiplier ratio, Santa Rosa additionally throttles back the FSB to 400MHz as well as reduce CPU/chipset voltages in less active states (such as DVD playback) in order to further save power consumption. At the moment though, there is only one speed setting for Dynamic FSB Switching. Santa Rosa will only switch between 800MHz and 400MHz. Initial tests on a prototype Santa Rosa notebook using CPU-Z did not show Dynamic FSB Switching at work though, so we might revisit this feature when the retail units hit the market.
Longer Residency in Enhanced Intel Deeper Sleep
Now, that is a very long sentence to digest, but what it really means is that Intel has found a way to keep the Santa Rosa Core 2 Duo CPU in its Enhanced C4 state longer than before, thus squeezing out every last bit of power they can save by having the processor in a constant shut down mode. Basically, when the CPU goes into the Enhanced C4 state, it is more or less completely turned off, and all data from its cache is flushed to the system main memory. However, in the past, whenever there are any data/cache hits or requests, the chipset will still snoop the CPU cache for verification, even when it is already cleared. This action wakes up the CPU (however briefly, but it still consumes power). With Santa Rosa, the chipset no longer wakes up or snoops into the CPU cache when it is in Enhanced C4 state and there is no real activity, thus achieving a 'Longer Residency in Enhanced Intel Deeper Sleep' (that's right, we said it again) and saving more power.