Things were going so well... and then it all came crashing down! The game wouldn't even run on our test system with 8GB of RAM and a 1GB virtual memory allotment. Indeed, the game crashed as soon as the benchmark drew exceeded a pagefile size of 9100MB, every single time, on every single card. Having more VRAM didn't help - this game is simply demanding tons of system RAM.
But before you cry havoc and let slip the dogs of war on the game's developers, keep in mind that the game works perfectly fine if you allow Windows to manage the virtual memory size for you. We found that the game actually required a total pagefile size of about 12GB, meaning that if using a PC equipped with 8GB of system RAM, you must allow the system to use at least 4GB of virtual memory.
Anyway, we weren't going to change the rules of our testing just for this game, so let's move on to the 16GB benchmarks.
Rise of the Tomb Raider - 16GB of System RAM
As we noted, we found some interesting memory usage patterns in our DX12 testing of this game, and they ended up being cited quite a bit around the 'net. Well, turns out it wasn't DX12, but Rise of the Tomb Raider's console-derived game engine that was the root cause of this phenomenon. Sure enough, during this round of testing, we again found that the game engine required between 13GB and 14GB of memory, adding up both RAM and VRAM. This is unlike anything we've seen on the previous pages, and we'd wager it's unlike anything seen in the history of PC gaming. Basically, it appears that RoTR is treating PCs as if they're using the same unified memory architecture as utilized by the Xbox One, on which it was first released.
And, how about the RAM-VRAM connection? Well, prepare to have your mind totally blown! The card using the most RAM is the one with the least VRAM, while the two cards using the least total memory are the cards with the most VRAM. Interestingly, those two cards, the 980 Ti 6GB and R9 390X 8GB, and in fact they are also using the least total memory as well.
So much for needing more system RAM when running with more VRAM. In this case, the opposite is true! Our guess is that this game first attempts to load all data in VRAM (as if it were a console system), and then moves to system RAM for overflow data, perhaps caching more than is necessary in an attempt to limit multiple writes to this slower memory bank.
Let's turn try sum up our disparate results and draw some conclusions about the RAM-VRAM connection!
We thought about averaging our results across our three games, but honestly, the mean would be meaningless, no pun intended, as the results are completely different depending on the game being used. Instead, we'll do a more qualitative summary.
First, we've seen that there is very little evidence that using a video card with more VRAM requires more system RAM. Certainly nothing remotely close to the the 2-to-1 ratio suggested in many enthusiasts forums. That being said, there was a slight tendency for our 2GB card, the R9 270X, to use less system RAM... at least in two of our games (The Witcher 3 and Battlefield 4). In a very strange turn of events, it used the most in Rise of the Tomb Raider, owning to that game's unique roots as an Xbox One exclusive harnessing the power of unified console memory. Furthermore, when comparing the R9 290 4GB to the R9 390X 8GB, or the GTX 980 4GB to the GTX 980 Ti 6GB, no clear pattern can be seen. If cards with more VRAM actually use more system RAM, the difference is essentially negligible.
Second, a system equipped with an Nvidia card typically uses more system memory than a system with an AMD card, on the order of 5% or so, based on the direct Radeon R9 290 4GB to GeForce GTX 980 4GB comparison. Because we didn't design our tests to tease out the difference between AMD and Nvidia cards in this regard, we don't have enough data to draw definitive conclusions on this issue. But honestly, we don't think this is a big deal, as it would end up affecting performance only in very specific edge cases. Furthermore, note that this finding definitely doesn't hold true for Rise of the Tomb Raider, which uses an entirely different (and new) approach to memory use.
We hope you've found this article helpful. Our findings here, along with all the other data we've collected over the years in the Gamer's Bench, helps us give you, our readers, the very best advice possible when planning your next PC upgrade. If you're in the market for a new PC, definitely stop by our Do-It-Yourself Buyer's Guides, updated on a monthly basis with the best-balanced builds at every price point!