Intel Dishes on Alder Lake-S: First x86 Hybrid CPU for Desktops

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The big.LITTLE CPU design comes to desktop PCs.

Among many other announcements (full breakdown here), Intel announced at its Architecture Day 2020 that the company would release its Alder Lake-S processors for the desktop PC in 2021. This marks the first time that Intel has brought its x86 hybrid architecture, which merges the use of both larger and smaller cores, to the mainstream desktop platform. Intel also unveiled the broad strokes of its Client 2.0 design initiative that will leverage more mix-and-match architectures in the future.

Intel's Alder Lake-S architecture features a design reminiscent of ARM's big.LITTLE (half-heartedly branded Big-BIGGER by Intel) with the larger cores used primarily for high-priority work, while the smaller cores execute less-intensive and background tasks and workloads. Intel didn't share many fine-grained details on the new chip, but did say Alder Lake-S will feature a combination of Golden Cove cores and Atom Gracemont cores. Given our current knowledge of Intel's roadmaps, we feel confident that these chips will come after the Rocket Lake chips that are next in line for the desktop PC.

Intel pioneered the x86 hybrid architecture with its Lakefield chips, with those inaugural models coming with one Sunny Cove core paired with four Atom Tremont cores. Intel designed Lakefield for mobile devices, so retaining a snappy, responsive feel to the device was important, but power efficiency was also of the utmost performance to preserve battery life. Intel says it will discard that efficiency focus for its Alder Lake-S chips and tune for performance instead, which would certainly be an easier task due to the enhanced power budget and more robust thermal solutions available on the desktop. 

A pair of higher-performance cores is a good place to start, and, compared to Lakefield, both the high- and low-performance Alder Lake-S cores take a step forward to newer microarchitectures. Alder Lake-S actually jumps forward two 'Cove' generations compared to the 'big' Sunny Cove cores found in the shipping Lakefield chips. The big Golden Cove cores come with increased single-threaded performance, AI performance, Network and 5G performance, and improved security features compared to the Willow Cove cores that debut with the Tiger Lake processors later this year. 

Meanwhile, Alder Lake's smaller Gracemont cores jump forward a single Atom generation and offer the benefit of being more power and area efficient (perf/mm^2) than the larger Golden Cove cores. Gracemont also comes with increased vector performance, a nod to an obvious addition of some level of AVX support (likely AVX2). Meanwhile, the larger Golden Cove cores should support AVX-512. That split instruction set support could portend optimizations to the hardware-aware scheduler in the operating system, which we'll cover shortly.

In its new roadmap, Intel also lists improved single-threaded performance for the Gracemont cores, but removed the “frequency” bullet point that was present when it unveiled the broad outlines of the Gracemont cores in 2018 at its previous Architecture Day. 

Intel hasn't indicated which process node it will use for either of Alder Lake's cores, or if they will come in a 3D-stacked package like the Lakefield chips. Aside from improved battery life, one of Intel's primary mobile-centric design aspirations for Lakefield was to reduce the footprint of the chip package. 

The smaller footprint on Lakefield enabled smaller, thinner, and lighter mobile designs by shrinking the size of the chip package with 3D stacking, but Intel doesn't have the same footprint concerns on the desktop. As such, Intel wouldn't necessarily have to use the cost-increasing Foveros 3D packaging technique to bring the processors to market. Instead, the chipmaker could use a single monolithic die with two kinds of cores, a chiplet-based architecture composed of separate compute chiplets for each type of core, or stick with 3D Foveros packaging. Only time will tell.
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