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Our attempt at overclocking the 4790K
I wanted to see what a regular dude could get out of the 4790K when overclocking, so I used a fairly typical sort of desktop PC setup, pictured below on our nifty open-bench platform.

That's an Asus Z97-A motherboard, which Geoff reviewed not long ago, and a Thermaltake NIC C5 dual-fan air cooler. Nice stuff, but not the most expensive gear by any means. That's the sort of thing we'd recommend in one of our System Guide builds.

My approach to overclocking this thing was simple. I used the firmware to do everything, not Windows tweaking software, and configured all four of the cores to run at the same speed. Then I raised the multiplier in order to change the clock speed. I fed the chip more core voltage as needed in order to improve stability. There are a number of secondary voltage settings one can tweak in order to increase the odds of a stable result, but I didn't mess with them. Asus' firmware auto-adjusts those voltages to some degree. I left those settings in "Auto" mode and accepted the extra help. Oh, and I cranked the CPU cooler's fans to their top speed and used the "Turbo" cooling profile in the Z97-A firmware.

I then tested stability in Windows by running Prime95 and using Asus' AI Tweaker software to monitor the CPU's state.

After a little trial and error, I was able to get our sample of the i7-4790K running all four cores stable at 4.6GHz with 1.375V. The Asus utility reported that the CPU was using 141W under load, a pretty dramatic increase from the 88W used at the stock voltage and frequency. With the NIC C5 fan cranked, the CPU temperatures settled in at about 71°C. The cooler's fans were spinning at around 2125 RPM, and as a result, they buzzed and whined very audibly with Prime95 going.

I then tried rebooting and pushing to 4.8GHz, but the system quickly locked. I dialed back to 4.7GHz, but still, no dice.

In the end, I had to push the core voltage up to 1.45V in order to get something approaching reasonable stability at 4.7GHz. The system would run Prime95 at those settings. AI Tweaker reported the CPU power draw ar 157W, but I don't think I trust that assessment. The NIC C5 is rated for 230W of cooling capacity, and the 4790K at 1.45V appeared to be right on the edge of what the cooler could handle. The CPU temperature creeped up slowly over time. After about 10 minutes, CPU temps ranged into the mid to high 80s Celsius, and then the Blue Screen of Death made an appearance.

Also, throughout the load test, I could hear the system reporting USB disconnects and reconnects, apparently involving the mouse and/or keyboard. Funky.

The 4790K was stable enough at 4.7GHz to run some benchmarks, but I'd say 4.6GHz is the more reasonable overclocking limit for daily use, unless you have a much beefier cooler than this one. The amount of extra voltage needed—and the resulting thermal load—isn't worth it.

For comparison, I then dropped my year-plus-old pre-release sample of the Core i7-4770K into the same system and cranked up its clocks. Guess what? It was happy to run at 4.7GHz using only 1.4V, a smidgen less voltage than our Devil's Canyon sample required. I tried to push higher, to 4.8GHz at 1.45V, but the 4770K wasn't having it. In the end, the 4770K was a little more comfortable at 4.7GHz than the 4790K, but the two were essentially equivalent in terms of max stable clock speeds. The temperatures of the two CPUs were comparable under load, too, although the 4770K was getting 0.05V less juice.

Of course, we're comparing just two pre-production samples in a world of possibilities, so your mileage may vary. Heck, it almost certainly will vary somewhat. I should note, though, that Nate's 4790K peaked at 4.7GHz, Marco's at 4.8GHz, and Hilbert's at 4.7-ish. So we are not alone on this front.

Anyhow, let's tale a quick look at how the 4790K performs, both at its stock speeds and overclocked.

Our testing methods

The test systems were configured like so:

Processor AMD FX-8350 AMD A10-7850K
Motherboard Asus Crosshair V Formula Asus A88X-PRO
North bridge 990FX A88X FCH
South bridge SB950
Memory size 16 GB (2 DIMMs) 16 GB (4 DIMMs)
Memory type AMD Performance
Series
DDR3 SDRAM
AMD Radeon Memory
Gamer Series
DDR3 SDRAM
Memory speed 1600 MT/s 2133 MT/s
Memory timings 9-9-9-24 1T 10-11-11-30 1T
Chipset
drivers
AMD chipset 13.12 AMD chipset 13.12
Audio Integrated
SB950/ALC889 with
Realtek 6.0.1.7233 drivers
Integrated
A85/ALC892 with
Realtek 6.0.1.7233 drivers
OpenCL ICD AMD APP 1526.3 AMD APP 1526.3
IGP drivers - -

 

Processor Core i7-3770K Core i7-4770K
Core i7-4790K
Motherboard Asus P8Z77-V Pro Asus Z97-A
North bridge Z77 Express Z97 Express
South bridge
Memory size 16 GB (2 DIMMs) 16 GB (2 DIMMs)
Memory type Corsair
Vengeance Pro
DDR3 SDRAM
Corsair
Vengeance Pro
DDR3 SDRAM
Memory speed 1600 MT/s 1600 MT/s
Memory timings 9-9-9-24 1T 9-9-9-24 1T
Chipset
drivers
INF update 10.0.14
iRST 13.0.3.1001
INF update 10.0.14
iRST 13.0.3.1001
Audio Integrated
Z77/ALC892 with
Realtek 6.0.1.7233 drivers
Integrated
Z97/ALC892 with
Realtek 6.0.1.7233 drivers
OpenCL ICD AMD APP 1526.3 AMD APP 1526.3

They all shared the following common elements:

Hard drive Kingston HyperX SH103S3 240GB SSD
Discrete graphics XFX Radeon HD 7950 Double Dissipation 3GB with Catalyst 14.6 beta drivers
OS Windows 8.1 Pro
Power supply Corsair AX650

Thanks to Corsair, XFX, Kingston, MSI, Asus, Gigabyte, Intel, and AMD for helping to outfit our test rigs with some of the finest hardware available. Thanks to Intel and AMD for providing the processors, as well, of course.

Some further notes on our testing methods:

  • The test systems' Windows desktops were set at 1920x1080 in 32-bit color. Vertical refresh sync (vsync) was disabled in the graphics driver control panel.

The tests and methods we employ are usually publicly available and reproducible. If you have questions about our methods, hit our forums to talk with us about them.