GPU overclocking changed with the release of Maxwell's updated architecture. The key aspects remain the same: Increase the clock-rate, play with voltage, increase the memory clock, and observe thermals; new advancements include power target percent and its tie to TDP. We recently showed the gains yielded from high overclocks on the GTX 980 in relation to Zotac's GTX 980 Extreme and the reference card and, in some instances, the OC produced better performance than stock SLI pairing.
This GTX 980 overclocking tutorial will walk through how to overclock nVidia's Maxwell architecture, explain power target %, voltage, memory clock, and more.
Tutorial: How to Overclock the GTX 980
NVIDIA GeForce GTX 980 & 970 Video Card Specs
||GTX 970||GTX 780 Ti|
|Texture Filter Rate
|Mem Config||4GB / 256-bit||4GB / 256-bit||3GB / 384-bit|
(9Gbps effective - read below)
Before getting started, these articles may interest you:
- The GTX 980 that we're using (technically, ours is branded by nVidia – they're the same, though).
- Zotac GTX 980 Extreme review + OC / SLI benchmarks.
- GTX 980 Reference review.
Overclocking Primer – The Concepts
We've previously written a CPU & GPU overclocking primer that explained the top-level basics of overclocking. I'll re-cover a few of those items before getting started.
All microprocessors operate on a timed “clock-rate.” This clock “ticks” with regular, predictable intervals – just like a wall clock would – and does so at a frequency. As you all know, CPU and GPU frequencies are measured in hertz, normally in the millions or billions of hertz. This unit of measurement can be translated as “oscillations per second” or “cycles per second,” so a 60Hz monitor would refresh 60 times per second; a 1500MHz core clock on a GPU would poll 1.5 billion times per second (1MHz = 1 million hertz). Now go look at a CPU with a 4.0GHz clock-rate – it's staggeringly impressive that such a small semiconductor can cycle four billion times per second.
Although there's a lot more at play that determines our performance – because frequency is certainly not everything – the core clock-rate is what we spend most of our time modifying when overclocking a GPU. “Overclocking” is specifically referring to the action of increasing the clock-rate over stock, a process that eventually requires “overvolting” to ensure stability.
There's a reason that the GPU doesn't just ship at its highest possible overclock, though.
Every GPU has a defined “stable baseline” that achieves the TDP, thermal, and stability targets established by the semiconductor manufacturer – that'd be nVidia or AMD, in the case of relevant gaming GPUs. Manufacturers may bin (sort) for higher-quality chips that will perform with greater stability at higher frequencies and voltages. There are still longevity and endurance concerns with high overclocks, so it's unlikely that manufacturers will pre-overclock GPUs into the numbers we can achieve manually.
What makes the GPU lose stability?
As frequency of the core clock continues to increase, the GPU will degrade in its stability. “Stability” has a sort of loose definition, depending on who's asked, but ours is very definitive: Any artifacts at all will be considered “unstable.”
A GPU with threatened stability due to overclocking will often exhibit soft failures initially, like blue flashes, texture tearing and artifacting, screen flickering, and driver crashes that are recovered. Push the clock still higher without compensating (with voltage) for stability and you'll start seeing hard crashes that require a cold boot or warm reboot.
Stability is threatened for a few key reasons: The clock can't handle the frequency applied at its current voltage, and thus fails to sustain a high clock-rate before power failure (or safety features kick-in); the temperatures exceed TjMax of the GPU (the maximum allowable safe temperature, as defined by nVidia or AMD); or watt draw is too high and has exceeded what the PCB and VRM are capable of supporting. Other reasons exist, of course, but there tend to be the most prevalent in basic overclocking.
Compensating for Stability with Voltage
A core concept of any overclocking is that of accompanying overvoltage. Every semiconductor receives some amount of voltage from its source of power (the power supply, in the case of PCs). The power goes through a Voltage Regulator Module (VRM), which we've explained in the past. This module is a collection of components, to include chokes, capacitors, MOSFETs, and a heatsink, and is responsible for “cleaning” the voltage supplied to the semiconductor.
VRMs are often measured on spec sheets as being a certain amount of phases – you might see 8+1 phase power design VRMs for motherboards. The number of phases can also (generally) be revealed by counting the number of exposed chokes on the PCB. When power is supplied to the board, it steps through each of these phases to temper the volatility of the power (“clean the voltage,” as we say); that power is then delivered to the GPU or CPU, hopefully in a stable enough state to sustain operation. A low-quality VRM will not sustain higher overclocks due to voltage increases that make it impossible for the cheaper VRM to keep up with demand.
Overclocking should always be done in steps. The general philosophy is to do some research first (if any exists yet) and determine a realistic expectation for your overclock. Do not commit this number to heart – every GPU is different, so it's possible that you've got a GM204 in your GTX 980 that binned out better (or worse) than what you're seeing online.
As a general rule, it's a bad idea to immediately apply the settings that someone online determined as stable for their GPU. Yours is different, and as such, this could be damaging or unstable to lift without incremental testing.
You'll want to step up the clock frequency first and without touching voltage, then find the point of instability. That's where we begin playing with other sliders. Let's look specifically at how Maxwell works.
Maxwell Overclocking Changes the Game
Maxwell introduced power percent increases over TDP. The GTX 980 has an advertised TDP of 165W, meaning it won't push more than that when at 100% stock TDP. Despite the advertisement, inspecting the card's BIOS with Kepler BIOS Inspector (and running wattage tests) reveals that the card actually draws closer to 180W when under max load. Not unexpected and not a big deal, but an important difference when making other calculations.
Even with a 180W TDP, the maximum power allowed by the GPU, VRM, and PCB is actually roughly 225W. It is possible to exceed this and stretch to upwards of 435W with the right hardmods and aftermarket design, like some of the manufacturers have done. The reference GTX 980 uses a 2x6-pin power setup and is capable of handling 225W of power, even though we read the TDP as 180W. We determine the 225W number in a pretty easy fashion: By opening an overclocking utility like EVGA Precision or MSI Afterburner, it is revealed that the power target percentage can be increased maximally to 125%. This means that the power supplied to the card from the PSU can be driven at 25% higher than stock. In other numbers, 180 * 1.25 = 225W. That's our maximum allowed power budget on the reference GTX 980.
We've heard of some reference cards, depending on BIOS iteration, that can only increase power to 110%.
All of this noted, Maxwell overclocking makes use of boost clock increases (overclocking), GPU vCore voltage increases (overvolting) for stability, and power target % as the core items to increase the clock. Memory clock can also be increased. Some software and hardware combinations will allow separate control of the memory voltage for fine-tuning, but this will only be found on extreme overclocking cards.
With Maxwell, overvolting becomes less important than previous and competing GPU architectures due to the power cap. There's only so much power (in Watts) to go around between the clocks and the voltage. We want to spend as much of this budget as possible on the clock-rate.
Warnings & Disclaimers
Overclocking carries a risk of killing the involved component(s). By overclocking irresponsibly or recklessly high, it is possible that your GPU will sustain permanent damage or become non-functional. Small overclocks are almost always entirely safe, but “going big” or attempts at extreme overclocking can damage or destroy components. Note that running a semiconductor at a high overclock for extended periods of time will also be detrimental to its longevity. You'll want to operate at a moderate overclock if anticipating long-term usage; if you're only using this GPU for a short period of time before upgrading, you'd be in OK shape to run it at a higher clock-rate.
We like to get the clocks as high as reasonably possible, benchmark it, and then drop down to something more moderate for extended use. Just to see how high we can get the numbers, really.
Continue to Page 2 for the tutorial for overclocking a GTX 980, including tools required for the job.