If you're keen to purchase some new gaming hardware for Christmas -- be it for yourself or someone else -- it might not be obvious what piece of tech to get. If your (or the giftee's) machine isn't playing the latest and greatest games at the best of frame rates, there are some rules of thumb that can help make the determination.
First, it's important to understand why newer games don't run as well on older hardware. Beyond the obvious considerations -- more detailed models, high resolution textures and post-process effects such as bloom and motion blur -- many modern games use a rendering technique called "deferred shading".
Without going into extreme details, with deferred shading, the graphics engine takes a snapshot of the player's current view every frame (so up to 60 or more times per second) that collects information about each visible object. This information can be anything from how far away the object is (its depth) to its colour and even the direction each individual pixel is facing.
What do these snapshots look like? Here are some examples from Fear Equation, a game I'm currently working on:
World normals -- basically the direction a pixel is facing, stored in an image's red/green/blue (RGB) channels.
Depth -- how far away each pixel is, relative to the camera, stored as a value from one to zero (or zero to one, depending on the engine). It has a greyscale appearance because 100 per cent RGB is white, while zero is black.
So naturally, the higher the resolution you play a game at, the more information generated per snapshot.
In simple terms, your GPU has to work harder at 1920 x 1080 (around two million pixels) versus 1280 x 800 (one million pixels). Also note that the graphics card may have to process these pixels multiple times per frame. So, if the game slows down dramatically when you increase the resolution, your GPU is the likely bottleneck.
On the other hand, if there's no significant change in frame rate when you alter the resolution, yet the game performs poorly, you'll want to look at upgrading your processor -- especially if it's a dual or single core. While games failed to take advantage of multi-core processors ten and even five years ago, almost all modern games make good use of the extra hardware.
And finally, your RAM. Insufficient RAM usually results in "stuttering". That is, the frame rate might be high, but when you look or move around in-game, the game will freeze for short bursts of time as data is swapped between your hard drive and the memory in your motherboard and graphics card.
If the game takes a long time to load in between levels or areas, look at getting more system RAM -- or even a solid state drive. If it tends to jerk around constantly, that's more indicative of low video RAM as textures and models are loaded in and out dynamically.