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Checking in on Intel's Core i7-5775C for gaming in 2018


The chip, the myth, the legend

Way back in the sands of August 2015, we got a rare sample of the exotic Core i7-5775C in the TR labs. This Broadwell CPU was unique—and remains unique—among Intel desktop chips because of its 128-MB slice of on-package embedded DRAM, or eDRAM. That on-package memory served as a large L4 victim cache for the entire CPU.

Intel includes eDRAM on processors with its Iris Pro integrated graphics processors to save them the trouble of having to depend entirely on system RAM for some types of graphics-related memory accesses, but that turned out not to be eDRAM's only benefit. Our testing at the time suggested that the i7-5775C's eDRAM sometimes gave it an edge in 99th-percentile frame times versus the Core i7-6700K, even as it was hampered by clock-speed deficits versus the Skylake part and a last-generation platform that could only use DDR3 RAM.


The chart that started it all

Since that time, the i7-5775C has developed a (possibly exaggerated) reputation among enthusiasts as a 99th-percentile frame-time monster unequaled by anything that has come before or since. Part of that may be our fault—we didn't test the i7-5775C much in subsequent CPU reviews. Broadwell desktop parts proved both costly and rare as hens' teeth at retail, and the eDRAM didn't deliver any notable productivity boost outside of gaming to warrant the extra cost. We generally recommended that people who weren't obsessed with the very best 99th-percentile frame times go with Skylake parts instead.

Perhaps in the absence of data, the i7-5775C's stature has grown to the point that enthusiasts still inquire about how its 99th-percentile-frame-time prowess holds up over three years after we uncovered its intriguing performance characteristics. Since people still ask, we figured we ought to answer them with our latest arsenal of CPU-bound games and frame-time measurement tools.

Before we address that question, though, I would temper the expectations of our eager inquirers a bit. A lot of water has flowed under the bridge in three years' time. AMD's Ryzen CPUs have thoroughly reshaped what the core and thread count of the mainstream PC looks like, and Intel has responded by adding more cores and threads to its own CPUs. The blue team has pushed single-core clock speeds ever higher, too, from 4.2 GHz on the Skylake i7-6700K to 4.9 GHz on the recently-launched Core i7-9700K or even 5 GHz on the Core i9-9900K.

The improvements haven't stopped there. DDR4 memory has gotten faster, and overclocked sticks running at 3200 MT/s are now a de facto enthusiast standard versus the 2133 MT/s RAM we first tested with Skylake. Nvidia has released two new graphics architectures in that time, as well, and mere $250-ish graphics cards now deliver performance similar to that of the $550-ish GTX 980 we used back when we originally tested the Core i7-5775C. In the high-end graphics-card market, the GTX 1080, GTX 1080 Ti, and RTX 2080 Ti have all set new bars for what's possible from a graphics card.

At least for gamers chasing the highest frame rates and lowest 99th-percentile frame times, those developments mean the ceiling for dizzying frame rates has gotten a lot higher, and that means CPU-bound games need a lot more oomph behind them to support the highest frame rates and lowest frame times. That's especially true of the single-threaded performance department, since that's how a lot of games that care about processor performance end up bottlenecked.

Given those developments, the i7-5775C doesn't look particularly well-positioned to get the most out of today's most demanding graphics cards, eDRAM or otherwise. It's long seemed unlikely to me that whatever magic led to its above-its-weight-class 99th-percentile frame-time performance in our initial review has held up. Four-core, eight-thread CPUs with DDR3 memory already trail their Skylake and Kaby Lake counterparts when we set up CPU-bound high-refresh-rate gaming experiences, and that eDRAM would have to do a lot of work to catch up entirely with newer chips.

See, Broadwell was never a high-clocking, power-hungry desktop beast (at least for mainstream systems). The 65-W i7-5775C's four cores and eight threads topped out at a peak speed of 3.7 GHz, and I've observed all-core speeds of 3.6 GHz from that chip under good cooling. Those figures were low when Broadwell and Skylake were new, and they're low now.


Slide courtesy Anandtech

The 5775C's eDRAM may have given its memory subsystem a boost when we were treading carefully with DDR4 speeds, but now that DDR4-3200 lets Intel's memory controllers approach 50 GB/s of unidirectional bandwidth in directed testing, the 50 GB/s of bidirectional bandwidth (100 GB/s in aggregate) that Broadwell's eDRAM cache offers might not be as impressive as it once was. Main memory latency for Intel chips is less of a concern than it used to be, too. Intel claimed that accessing eDRAM would require 30 ns to 32 ns when it combined the Crystal Well eDRAM die with Haswell CPUs. That's still a fair bit quicker than the 43 ns to 45 ns we record with today's swiftest Intel chips, but it's not as far off as CPU memory controllers used to be.

For an idea of the shape of the CPU market today, even our gaming-value favorite, the $200-ish Core i5-8400, has an all-core boost speed of 3.8 GHz. Its Skylake cores are fabricated with a twice-improved version of Intel's 14-nm process. It benefits from DDR4-2666 at a minimum, and it can be paired with even faster RAM if you opt to run it on a Z370 motherboard. We already spoke of Coffee Lake and Coffee Lake Refresh Core i7s, where chips that bear stickers similar to the i7-5775C's $366 to $377 suggested price boast peak single-core clock speeds in the range of 4.7 GHz to 4.9 GHz. That's nothing to sniff at if you're after the best high-refresh-rate gaming experiences, even if the i7-5775C can be overclocked to make up some of the difference.


A sampling of Core i7-5775Cs on eBay as of this writing

Even if the i7-5775C did deliver exceptional performance and you did want to take the plunge on one of these chips to underpin your 2018 gaming system, it's not as though these chips are abundant or inexpensive. Three i7-5775Cs are on eBay as I write this, and buyers want anywhere from $329.95 to $350 for their wunderchips. New-in-box models of the Z97 motherboards you'd want to run this chip are no longer available at e-tail, although used boards remain reasonably priced on eBay—a pleasant surprise, if you've gone shopping for vintage Intel motherboards of late. Enthusiast DDR3 RAM isn't much cheaper than run-of-the-mill DDR4-3200 modules, though.

Prices for Intel's latest enthusiast chips have risen recently thanks to supply issues, to be sure, but one just wouldn't be saving a ton of money on the road to hypothetical 99th-percentile bliss by getting onto a 2014-era platform. You could miss out on features we take for granted these days, too, like reliable NVMe boot (which has never worked consistently on our Z97 testbed), PCIe 3.0 lanes from the chipset, USB 3.1 Gen 2 ports, and much more. The fact is that a four-year-old PC is still a four-year-old PC, and we couldn't in good conscience recommend that users start with such an aged platform unless the i7-5775C was still delivering indisputable miracles for gaming performance.

I've just finished reviewing and testing a wide range of Intel processors for our Core i9-9900K review, and our frame-time digestion tools are warmed up and hungry for more. I figure now is as good a time as any to see how much of the i7-5775C's magic remains. I've dusted off our trusty Z97 motherboard and DDR3 RAM to see what happens when you ask a modestly-clocked quad-core with eight threads and a massive cache to drive today's single most powerful video card. Let's find out.