Desktop ram and graphics cards play 2 different roles but both are vitally important.
First off, you have plenty of ram, 5GB worth. What does this do for you? Well, ram holds all data it has processed in a game. So lets say if your out on a watch tower looking out towards a beach. 2 minutes later your in a jungle. The 5GB ram is still holding the information of you looking out towards the beach. That way when its time for you to go back to the beach, it will already have that information readily available to access for the graphics card and the cpu. If it doesn't pull it from the desktop ram, its pulling it from the hard drive which is slow as hell to get information from, hence you'll experience a drop in fps or at times small spirts or jolts in gameplay because its loading new material. If you don't have a good enough size ram, it dumps previous scences you visited and adds in the new ones your at, however because it doesn't have enough ram size (lets say you only had 500mb), then the old information is lost and it has to go back to the harddrive and then to your ram, and then to your cpu and gpu to eventually render on your screen. While it all occurs in miliseconds, all those miliseconds add up to the point where you recieve jolts and jerks in new areas and even previously visted ones while in game.
Now as for a graphics card ram. It plays the same role as desktop ram except that it holds the more used information. If you been staring at a tree for 10 minutes in a game, more than likely its in your GPU ram because thats the data thats being sent to the graphics card. It processes data thats on screen right then and there. When you go to past visited area's, and more than likely the ram won't hold all of it, it will go to your desktop ram, send it to the gpu and work from there. Keep in mind, gpu ram is generally faster than desktop ram. This isn't always the case if you know what your buying. However, video memory isn't such a big deal.
Overall, thats just the issue of ram. When it comes to the gpu itself, that plays a big factor on your fps. I'll give you a example in Crysis. I played it with 1 GB ram while the requirements were 2GB. I had squirts and jerks all over the place. When I fired my weapon, when I did a quick U-turn, ect. It felt like lag from hell. When I upgraded my ram, my fps stayed the same, but all the jerks and kinks went away, because the data was readily accessed because I had enough ram.
You won't experienced jerks or such things with 5GB of ram, but you won't achieve great fps either. If you want higher fps, you'll need a better engine (graphics card) to do it for you.
If you do go GPU shopping, you have plenty of ram, so no need to worry about how much of its on your gpu. What you want is the FPS it can crank out. Just go to toms hardware or other sites that show you benchmarks on all the games they done.
· 1 decade ago