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Intel's Core i7-5960X processor reviewed

Haswell Extreme cranks up the core count

For a PC hobbyist who's into building high-end systems with elaborate water-cooling setups and multiple GPUs, it doesn't get any better than Intel's Core i7 Extreme processors. They're pricey, sure, but they're clearly the fastest, most capable CPUs on the planet.

Except, you know, when they aren't.

The last generation of Intel's Extreme CPUs lost much of its luster earlier this year when the Devil's Canyon chips arrived in mid-range desktops with higher clock speeds and sometimes superior performance. It didn't help that the Core i7-4960X and friends were saddled with the older X79 chipset, whose selection of USB and SATA ports left much to be desired.

Happily, Intel has been cooking up a new high-end platform that should remove all doubt about who's top dog. The CPU is known as Haswell-E, and it brings with it an updated companion chipset, the X99. Together, this dynamic duo offers more of absolutely everything you'd want in a high-end rig: more cores, larger caches, and a huge increase in high-speed I/O ports. Haswell-E is also the first desktop CPU to support DDR4 memory, which promises faster transfer rates than DDR3.

We've been waiting impatiently for Haswell-E's arrival for most of the year. At last, it's finally here. We've had the top CPU in the lineup, the Core i7-5960X, up and running in Damage Labs for a while now—and we've tested it more ways than is probably healthy. Read on for our in-depth assessment.

The E is for Extreme
Compared to the prior-gen Ivy Bridge-E chips, the new Haswell-E silicon is an upgrade on just about every front—except maybe one. Both chips are built using Intel's 22-nm fabrication process with tri-gate transistors. Intel is on the cusp of releasing 14-nm chips for use in tablets and laptops, but these big chips probably won't move to the new process for another year.

The most notable change in Haswell-E is embedded in its name: the transition to newer CPU cores based on the Haswell microarchitecture. Compared to Ivy Bridge, Haswell cores can execute about 5-10% more instructions in each clock cycle—and possibly more if programs make use of AVX2 instructions for fast parallel processing. Haswell also brings its voltage regulation circuitry onto the CPU die, which can allow for faster, finer-grained control over the delivery of power around the chip.

A look at the Haswell-E die. Source: Intel.

Those improvements are welcome, but Intel hasn't left anything to chance. The Core i7-5960X packs eight cores, and its L3 cache capacity is a beefy 20MB. That's two more cores and 5MB more cache than the prior-gen Core i7-4960X, which should be enough to ensure the new chip's performance superiority in multithreaded workloads.

To feed all of those cores, Haswell-E can transfer tremendous, almost unreasonable amounts of data. One of the key enablers here is DDR4 memory, which offers transfer rates of 2133 MT/s on these first products—up from DDR3 at 1866 MT/s in Ivy-E—and promises to scale up from there. Haswell-E has four memory channels, so it's starting with 68 GB/s of memory bandwidth. In theory, that's 20 GB/s more than the last gen. That's also, coincidentally, the same amount of memory throughput the Xbox One has dedicated to both its CPU cores and graphics.

Speaking of graphics, one of the big selling points for these Extreme platforms is PCI Express bandwidth for use with multiple graphics cards. Haswell-E doesn't disappoint on that front, with 40 lanes of PCIe 3.0 connectivity coming directly off the CPU die. The CPU can host multi-GPU configs with 16 lanes dedicated to two different graphics cards—or up to four graphics cards with eight lanes each. That's the same basic config as in the last gen, with a few tweaks. One change is the ability to host a 5x8 setup, if the motherboard is built to support it. Indeed, the Asus X99 Deluxe board in our test system has five PCIe x16 slots onboard. I'm not quite sure what you'd do with five graphics cards at once, but it is apparently a possibility now.

Code name Key
Threads Last-level
cache size
Process node
Gulftown Core i7-9xx 6 12 12 MB 32 1168 248
Sandy Bridge-E Core-i7-39xx 8 16 20 MB 32 2270 435
Ivy Bridge-E Core-i7-49xx 6 12 15 MB 22 1860 257
Haswell-E Core-i7-59xx 8 16 20 MB 22 2600 356
Vishera FX 4 8 8 MB 32 1200 315

All of this beefy hardware makes for a complex chip. Haswell-E is certainly that, at roughly 2.6 billion transistors and 356 mm². The quad-core Haswell chip is only 177 mm², or about half the size, and that's with integrated graphics. You can see the difference in the dimensions of the packages used for the socketed processors below.

The quad-core Haswell Core i7-4790K (left) versus the Core i7-5960X (right)

Yeah, this is big and substantial hardware. Here's a look at the three new Haswell-E-based CPU models alongside their quad-core Haswell cousins.

Model Cores/
& max
Core i7-5960X 8/16 3.0 3.5 20 40 4 DDR4-2133 140 $999
Core i7-5930K 6/12 3.5 3.7 15 40 4 DDR4-2133 140 $583
Core i7-5820K 6/12 3.3 3.6 15 28 4 DDR4-2133 140 $389
Core i7-4790K 4/8 4.0 4.4 8 16 2 DDR3-1600 88 $339
Core i7-4690K 4/4 3.5 3.9 6 16 2 DDR3-1600 88 $242

The Core i7-5960X gives up some clock frequency to cram eight cores into its 140W power envelope. Those base and boost clocks of 3.0 and 3.5GHz are down quite a bit from the 3.6/4.0GHz speeds of the Core i7-4960X. Even with Haswell's per-clock performance improvements, those lower frequencies will have consequences in workloads that don't scale up to 16 threads perfectly.

As usual, Intel charges a big premium for its top-end processor. You're probably better off buying the Core i7-5930K for over 400 bucks less, as long as you can live with "only" six cores (and 12 threads via Hyper-Threading.) The 5930K has the added advantage of slightly higher clock speeds, too. Then again, I'm not sure how much stock clocks matter since all of the X- and K-series parts shown above come with unlocked multipliers for dead-simple overclocking.

One product you'll probably want to avoid is the Core i7-5820K, which Intel has ruined by disabling a bunch of the PCI Express lanes. I swear, if there's a way to tune a knob or dial in order to gimp a CPU for the sake of product segmentation, Intel's product people will find that knob and turn it, no matter what. In this case, the Core i7-5820K loses the ability to host a dual-graphics setup with 16 lanes to each PCIe slot. Have fun explaining that one to your friend who popped $389 for a CPU and about the same for a fancy X99 motherboard, only to find that it's no better—not even in theory—than a 4790K for dual-GPU setups. This issue is more pressing now that AMD relies on PCI Express bandwidth for transferring CrossFire frames between GPUs.

We have in the past considered CPUs like the Core i7-3820 to be a nice entry point into Intel's higher-end platforms. That ends here. The 5820K's hobbled PCIe removes a major rationale for the X99 platform's adoption among PC gamers. Unless you really know what you're doing, stay away from it.