My SLI Saga

I bought a customized Gaming PC so that I could expand it in the future. Most importantly, I wanted to swap out the graphics card for a newer model in a few years when mine started to struggle. I also wanted the option to combine multiple graphics cards together. This is called SLI (or Crossfire for AMD folks) and allows multiple graphics cards to work together as one, nearly doubling performance in some games. I already had to swap my motherboard for an “SLI certified” one when I ordered my system in December but after that I thought I was all set. My idea was that some time in the future I’d purchase another NVIDIA GeForce GTX 970, pop it into my machine, max out all of my quality settings, and live happily ever after. Yeah.

Before I get into my saga, let’s talk about SLI a little bit first. SLI is more restrictive than ATI’s Crossfire technology. First it requires a certified motherboard which increases cost a little bit. If you don’t have a certified motherboard, SLI won’t work, even if the motherboard meets all of the other requirements (basically two PCI Express 3.0 x16 slots).  Second it only works with cards containing the same GPU; that is if you have a GTX 970 you must SLI with another GTX 970 card, not another 900-series card like a 960 or 980. Crossfire lets you mix cards of the same chip family, meaning that you could mix cards with any of the 13 different R7 or R9 chips on them. I ended up with SLI because I bought an NVIDIA card because of its incredible price-to-performance ratio so I have to live with the restrictions.

While SLI requires cards with the same exact GPU it does not require the cards to be the same model or even from the same vendor, supposedly. So when I decided to buy a second GTX 970 so that I could run Far Cry 4 at maximum quality settings at 1440p, I wasn’t concerned about which exact card to buy; I just wanted one that had a 970 on it. Still I decided to purchase one from the same manufacturer of my existing card just to be safe. If cards from different manufacturers could SLI then I should have had no problem with two cards from the same company.

I ended up buying an EVGA GTX 970 SSC ACX 2.0+ to complement my existing EVGA GTX 970 SC ACX 2.0. Now what exactly is the difference between those cards you ask? Well, about $20, additional overclocking (+25 MHz hence the additional ‘S’ in SSC which stands for super super clocked), an even more improved fan assembly (the + in ACX+), and revised power circuitry for improved overclocking potential. Overall the card wasn’t too different than my existing card, or so I thought. When I took it out of the box I noticed that it was about ½ and inch longer than my existing card, had more DisplayPort outputs, and had an additional two pins in its auxiliary power connector. I thought they were just minor differences in card models.

When I booted up my system and opened the NVIDIA control panel to enable SLI, I was confused as the only option I had was to operate each card on a separate monitor. The “maximum performance” option that enabled both cards for one display was disabled and there was a message about the SLI bridge connector not being detected (which I had installed). After hunting through the internet and finding similar stories about SLI issues not only with different brands but different cards of the same brand the only solution I could find was to use a driver hack to enable it. Unfortunately the hack didn’t recognize the SLI bridge connector so I’d never be able to get full performance out of the two cards.

I did a bunch of reading over a few days and finally came across a forum post with a link to an EVGA support article explaining how different models of their GTX 970 cards were not compatible for SLI. It included a handy-dandy chart that showed the three groupings of compatible cards. Alas my original card was from one grouping and my new card was from another. Ugh. So much for an easy install.

I considered returning the card to Newegg but they were going to charge me a $52 restocking fee, so I decided to purchase the same card again from Amazon. If I ran into issues again Amazon would accept a return with no hassle and no fee. I’ll sell my original card on eBay or Craigslist. Thanks to the driver hack I found I was able to get a preview of SLI performance and it was really nice, even if it wasn’t at its full potential. I was able to crank up the details in several games and enjoy great frame rates. Of course the most recent Far Cry 4 update caused a bunch of issues with SLI, but that’s another story for another time.

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