What makes a GPU fast?

Posted: April 3, 2011 by ryanlecocq in Technology

Update 11/14:  Since people keep reading this, even though it’s ancient, I’m re-writing and simplifying it.

Although I wouldn’t by any means call the GPU numbering systems of today ideal, they are at least better than when I originally wrote this article.   In both AMD and NVIDIA, the 50 mark is generally accepted as the basement for a card designed to play modern games.  By this I mean a Radeon 250 or a Geforce 850 are the minimum cards in their series at which you can run current games without minimizing all settings.  Cards below the 50 mark are mostly geared towards HD media and casual games.  If you want to do serious gaming, you want to be above the 70 mark and for HD+ resolutions or multiple monitors, you need a top end card or two upper mid range ones.

The big caveat here is Intel integrated graphics.  It used to be a general rule that you couldn’t play games on Intel graphics, period.  The newer versions though, are actually able to run many popular games at decent settings.  The numbering scheme is at least as confusing as past AMD ones, but I can generalize.  The HD 4000 series in the 3rd gen i-series processors are capable of low-end settings on most modern games.  You’ll have to run at low-ish resolutions, but the games will be generally playable.  The 5000 series Iris and Iris Pro graphics are capable of mid-range and occasionally higher settings on a single monitor.  While performance is inconsistent as most games are optimized for AMD and NVIDIA’s much more robust drivers, the higher end integrated chips will even keep up with mid-range dedicated cards on certain games.

One thing from the original article that is still true and always will be until graphics processing changes dramatically, is the importance of fast VRAM.  Even to this day, many budget cards will use slow DDR3 memory or DDR5 at only 64-bit.  How much VRAM you have is definitely important, but only if you are comparing apples and apples.  VRAM bitrate directly correlates to texture fillrate, which is one of the main yardsticks of GPU capability.  So the above rules of thumb about GPU series can go out the window if you are comparing two cards with different memory types and speeds.  It’s easy to be tempted by a cheaper card that has overclocked cores but slower memory.  A 10% overclock on the GPU cores will make nowhere near the difference that 128-bit vs 256-bit VRAM will.

The real question for most of us is whether to go with one better card or two lesser ones.  It’s important to keep in mind that you are only doubling the shader count and the potential interface bandwidth.  The VRAM and often the video outputs of the second card are not used.  So if you were to get a single card with twice the performance, you would probably be saving on power, noise and space for other cards and connections.  The consideration of power is more than just Wattage as well, because you need anywhere from 2-6 PCI-Express connectors on your power supply to run multiple graphics cards.  Not only is that a lot of power, but also a lot of large cables running through your case.  As a general rule, I only recommend SLI or Crossfire for full tower case setups.  Smaller builds would be better served with a higher performance single card.

For smaller systems there is one interesting little tweak that’s an oldie but a goody: a secondary low-power card for physx or low-power use.  That’s right, I bet you never considered using switchable graphics on a desktop.  There are now quite a few games that use NVIDIA’s physx for physics processing.  There’s also the fact that a GTS 450 is a lot more energy efficient than a high-end card, even when the high-end card is running at its’ low power setting.  Considering older midrange cards are cheap, the energy savings will pay off the cost pretty quickly, even considering the extra use for physx.  You can easily select which card should be used in each game’s profile in the NVIDIA control panel.  Also, this does not require an SLI bridge or generally an extra power connection as most of these cards don’t require secondary power.  The one huge pain though, is that you need two connections to the monitor.  This is no big deal if you have DVI and HDMI or multiple of either on the same monitor, but makes this not worth it otherwise.

That’s about the most simple and straightforward layman’s guide I can make.  All of the information discussed in this article is featured in the product page of any graphics card, so you shouldn’t need to look far to make a relatively informed decision.

  1. Russell says:

    I never knew any of this.. thanks for the info =) I have and SLI mother board with a GTX 465 graphics card. if i was going to add another GTX 465 in the future which i do plan to, would i need to increase my power supply ? seeing as there is an extra card

    • ryanlecocq says:

      What is your current PSU wattage? The GTX 465 is an extremely high power draw card at 178-345 watts. Unless you current PSU is 1000 watts or so, you’ll probably need to upgrade. Geeks.com is usually your best bet on power supplies as they usually beat Newegg by about $10.

      • ryanlecocq says:

        Really good choice by the way. You’ll notice in my previous GPU article I recommend to anyone under the $200 mark to save up for a 460 or 465. They are the best bang for the buck period right now in cards. True that power draw is roughly 35% higher max than the competing ATi HD6850, but the 465 has unbeatable fill rate.

        For now I would say just ride it out, since you’re GPU is likely not holding you back, even at the highest settings. The GTX465 benchmarks at 75.6 on Crysis 2 in high settings, so if you’re getting less, it’s your CPU holding you back.

        Once the ’60’ series of the GTX 500s comes out, it will drop 30-50% in price making it REALLY the best deal out there as the 500s only offer a few optimizations for DX11.

      • russell says:

        I think its 600 Wattage. To be honest, i think i either have a problem with my processor or its my green HHD it goes quiet slow on start up, not sure what thats about.

  2. ryanlecocq says:

    Well one thing that can slow a computer down on startup is too many processes initializing. If your PC is clogged up with bloatware and malware that can make it take a long time before the computer is up to full speed.

    As far as PSUs, if you get another GTX 465 you will need to upgrade to a 1000watt PSU. The one you have should be plenty though for gaming. If you are doing powerful rendering you can see some benefit from SLI though.

    I mentioned in a previous article that the best way to test what part of the system is causing the bottleneck is by changing settings within a game. For example in World of Warcraft there are some settings that are CPU dependent, some that rely on RAM and others which rely on the GPU. By turning the settings related to each part to the max and turning the others to the minimum and comparing framerates, you can find out what’s holding you back.

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