Yonah
Yonah
Yonah, stating the obvious, is Intel's first mobile dual-core CPU. It's also the first mobile architecture that's been fabricated on a 65nm process, and, as such, packages two cores on to a single piece of silicon that's presented in a S478 form factor which, it seems, will be electrically incompatible with the present Dothan. There's also 2MB of L2 cache, and a total of 151-million transistors that all fit into a die size of 90.3mm²; that's less than a centimetre squared for those not too hot on their maths, and only marginally larger than the single-core Dothan's 84mm².
The basic architecture generally follows Intel recent approach, that is, have multi-core CPUs sharing a single bus that communicates with the chipset. All Yonah CPUs will also run off a 667MHz Front-Side Bus, up from the Dothan's 533MHz and Banias' 400MHz. Extra bandwidth should help give it a slight performance advantage in most memory-sensitive single-threaded applications over the present Dothan, and bandwidth will be that much more important with two cores to keep satiated. Each core also carries its own digital temperature sensor for better fan control, although the CPUs will also use an existing thermal diode as backup.
Intel Digital Media Boost
Each Yonah core isn't simply a Dothan clone manufactured on a smaller process. Falling under the name of Intel Digital Media Boost, Chipzilla has taken the opportunity of augmenting the feature-set by including support for SSE3 (Streaming SIMD Extentions 3, 10 for Yonah), first debuting on the desktop Prescott core, which increases the computational speed for certain mathematical calculations. Intel also states that general SSE2 decoder throughput has been improved, as well as other behind-the-scenes SSE/SSE2 optimisations. There's no word on EMT64, the desktop technology that allows most LGA775 CPUs to process 64-bit applications and it's unclear whether Yonah CPUs will support Intel Virtualization technology, either. Could they be reserved for Intel's next-generation Merom CPU, slated for late '06 release?
Shared cache
The present Dothan core has access to 2MB of L2 cache, handy for moving data at superfast speeds to the CPU. Yonah, however, continues with the basic L2 cache from the Dothan, but rather than split it into 1MB chunks for each core, gives both execution cores access to the 2MB. The desktop Pentium Extreme Edition 955 (Presler), for comparative example, gives each core exclusive access to 2MB of L2 cache. This shared cache setup, dubbed Intel Smart Cache, provides either core access to the entire L2 cache when the other is idle, and dynamic cache allocation feeds each core, concurrently, depending upon load. All in all, a better cache implementation than the division present on desktop dual-core models, and we're sure that a shared-cache setup will be included in future multi-core CPUs. As an aside, a power management unit, residing between the two cores and shared cache, keeps power and access ticking along efficiently, too.
Power-saving techniques
Intel is at pains to point out that Yonah is more than just better benchmark performance. In an attempt to prolong the ever-important battery life, especially with two cores chomping at the bit, Yonah packs in Intel's EIST (Enhanced Intel SpeedStep Technology) that works in conjunction with a couple of new features. The first, dynamic cache resizing, flushes the L2 cache contents to main system memory during periods of little or no activity. Power-eating, flushed L2 cache (with contents now in main memory) is then turned off and the CPU put into a lowest-power state (DC4 - deeper sleep) which falls under the Dothan's C4 (deep sleep). Basic power-saving, where each core's speed is reduced, can be done independently, but both cores still operate on the same voltage plane, and one cannot be turned to, say, low-voltage C4 when the other is at higher-voltage C1.
Naming scheme
Intel's abandoning the present naming scheme employed on current Dothan CPUs. Pentium M 780, for example, refers to a Dothan single-core CPU that ticks along at 2.26GHz and has a 533MHz FSB. The new naming system takes into account the single-core and dual-core Yonah CPUs and differentiates between them by branding them either Intel Centrino Solo and Centrino Duo (duh!). Following on from that, an alpha prefix will denote the power class of the CPU, with U for ultra-low voltage, L for low-voltage, and T for performance models. Finally, a four-digit number will specify the speed. So, for example, an Intel Centrino Duo T2600 equates to a dual-core Yonah (performance series) with a clock speed of 2.16GHz. We'll publish a complete list of processors in due course.
