Coffee Lake hasn't officially arrived, but Intel has confirmed enthusiasts' fears and information we ferreted out from public statements from motherboard vendors: The processors will not be backward compatible with the Z270 or Z170 chipsets. The forced move to the Z370 platform, even though Coffee Lake processors drop into the physically identical LGA1551 socket found on previous-generation motherboards, stands in stark contrast to AMD's Socket AM4 strategy, which the company will support with all new processors until 2020. AMD announced AM4 last September, and it also supports AMD's 7th-generation Bristol Ridge (the Carrizo-based APU).
Kaby Lake processors brought most of the iterative improvements over Skylake that we've come to expect, but you could purchase one of the new fancy processors and slap it into an existing Z170 motherboard and enjoy the increased performance with a minimal investment, albeit after a BIOS update.
In contrast, Coffee Lake offers Intel's biggest generational performance leap we've seen in years, if the company's claims hold true. Suddenly we have quad-core i3s and hexa-core i5s and i7s, breaking Intel's insistence upon merely offering slightly increased clock speeds (and perhaps improved integrated graphics) for its gen-on-gen releases. Of course, there will be a slight price increase associated with the step up to more cores, but the ability to drop a new processor into the Z270 motherboard you bought eight months ago (at the earliest) would be nice.
But Intel isn't providing backward compatibility with either of the older LGA1151 motherboards (Z170 and Z270) and, curiously, your only upgrade path through the end of the year comes in the form of pricey Z370 motherboards—value-oriented B350 or H370 motherboards will not debut until next year.
Intel provided a few technical reasons for the lack of backward compatibility, with the requirement for an improved power delivery subsystem being one of the most important. We know that the existing Z270 motherboards can provide enough power to push quad-core processors, as we see now with the Coffee Lake Core i3 processors, but Intel noted that the additional two cores proffered on the i5 and i7 would require more power.
Although TDP isn't a direct measurement of power consumption, it is a decent indicator. The Coffee Lake i7-8700K weighs in with a TDP of 95W compared to Kaby Lake i7-7700K's 91W rating. A small increase, sure, but we could see larger deltas during overclocking. Intel says it improved the package power delivery to offset the increased overclocking power requirements for the six-core models, and we will certainly quantify the difference in package power draw during our review. The Coffee Lake processors also support per-core overclocking, a feature that wasn't included in the Kaby Lake era, but they still don't allow for fine-grained per-core voltage or P-State settings.
Intel noted that the Z370 motherboards have improved memory routing to support DDR4-2666, a slight increase over Kaby Lake's DDR4-2400. Existing Kaby Lake motherboards easily support memory overclocking well beyond DDR4-2666, as any overclocker can attest, but Intel also says it has baked other improvements into Coffee Lake processors. Intel expanded the memory multipliers to support up to 8400 MT/s and added a real-time memory latency control feature.
Whether the existing Z270 motherboards, many of which offer beefy power delivery, could potentially satisfy the needs of the Coffee Lake processors will be a hot-button debate for some time to come. We've requested additional details from Intel regarding the socket and pin-out, but we await further details.
The 300-series chipset doesn't offer any new features; even the TDP remains the same, which suggests the 300-series chipset is merely a Z270 refresh. Outside of new LED functionality or other third-party additions, there would be little reason to upgrade a Kaby Lake system to a newer motherboard, but the option would be nice. However, Kaby Lake processors will also not work on 300-series motherboards. Intel indicated the decision to eliminate Kaby Lake compatibility was due, at least in part, to requests from motherboard vendors that the company make a "clean split." For motherboard vendors, this removes the burden of adding support for Kaby Lake (and the requisite validation) during a time when most motherboard vendors are already stretched to their engineering resource limits due to rapid fire Intel and AMD launches.
The requirement for a new chipset also comes hot on the heels of rumors that Intel will have Z390 motherboards coming to market next year that support eight-core processors. Even though the similar naming convention would lead us to believe Z390 motherboards will work with Coffee Lake chips, it's hard to speculate until we know more. Intel is placing the Kaby Lake refresh, Coffee Lake, and Cannon Lake processors under the 8th-generation umbrella, so it's possible the Z390 motherboard will support Cannon Lake processors. Will Z370 motherboards support Cannon Lake processors? That's anyone's guess.
The staggered 300-series roll out (there won't be any H370 or B350 motherboards available until next year) also means that enthusiasts interested in Intel's locked Coffee Lake models will still have to pay extra for Z370 motherboards that support overclocking.
There has been plenty of speculation that Intel's Coffee Lake lineup is a direct reaction to AMD's Ryzen processors, but given the extended nature of processor development, the processors have likely been in the works for several years. While Coffee Lake may not be a knee-jerk reaction, the fact that Intel doesn't have the full lineup of motherboard options at launch certainly makes it appear the company pulled the timeline in significantly.