Why are my Games so Slow?

For most computer applications, like e-mail, web browsing or office programs, speed depends largely on available RAM and the model of installed CPU. The reasons for this are not technically complicated. E-mail, web browsing and office programs don't depend on the kinds of performance that games require. Games require quickness in control response and video display rates.

Video games graphics have been produced pretty much the same way since the release of the original television video game consoles in the early 1980s. The original consoles relied on something called a "vertical sync" in order to update the graphics display on the screen.

The scan lines on old tube-based televisions were drawn one after another from the top of the screen down to the base, and then the ray emitter would blank the screen so it could travel back up to the top. During this interval, called a "v-sync" or "v-blit," video memory could be manipulated without it being visible on the screen. By changing the pattern of the display during each vertical refresh, the screen could be manipulated to make it appear as if the display is animated. Almost exactly the same system is used to create the illusion of animation in most every game or graphics display.

In a digital display, however, there is no vertical sync, so how can the screen be updated to make it appear as if the graphics are animated? Without a vertical sync, there is no such thing as a screen "refresh" so technically, there should be no way to redraw the screen while it is refreshing. But, this is a digital display, so there is a more efficient way.

In a digital display, it is possible to keep two complete representations of video memory intact at all times. The first memory image is the one currently on the screen, and the second image is maintained only in system memory and not visible on the screen. All of the game mechanics that must make changes to the display are programmed only to make changes to the video image that is in system memory, and not the one in video memory. During each screen refresh, the system image is "blitted" to screen memory, leaving a copy of itself as the system image so the next frame can be drawn. This produces the image of animation, because the display image is always the most current representation of what the game programming says should be displayed.

For the most recent of the recent games, an even more efficient system has been developed. Instead of maintaining one memory image as the display and a second image in system memory, larger video card memory capacities have made it possible for both memory images to be maintained in video memory, with both contained on the video card. This has a dramatic effect on the speed of the display refresh because the CPU is no longer required to move display data across the system bus from system memory to video memory in order to update the display. In fact, with all of the video images maintained on the video card there is no reason to move the information at all.

The most advanced game engines can now send instructions directly to the video hardware while maintaining all of the graphics data inside video memory. This allows for maximum speed, because there is no need to move data inside the system at all.

So what does this mean for game speed? Well, the obvious first point is to maximize the amount of video memory available while being sure not to just spend money on a bigger number. It isn't necessary to have 8GB of video memory, for example, because there is no PC display large enough to require several gigs of RAM to hold a video image in memory. For older games, it is also important to consider the bus type and bus speed of the card, because some older game engines cannot take advantage of "all-video-memory" features. They still need to move data from system to video memory, and that requires a faster bus like PCI Express, for example.

The third point, like any PC system optimization, is to make sure there is as much RAM available as possible. If a game has to swap to disk, it will destroy performance. Most game engines don't require enormous amounts of system memory, but game media, like audio files, video files and textures do require large amounts of fast memory to maximize performance.

As strange as it may seem, CPU speed isn't really as much of an issue now as it used to be for PC game performance. The reason for this is much of the math for most game engines is done in video hardware as opposed to software run by the CPU. This frees the processor to do things like context switching and interrupt processing much faster than would otherwise be possible if the processor had to simultaneously do three-dimensional display math.

So if your games are slowing down, be sure to check the three parts of your system that can maximize graphics performance: video RAM, video card bus and system RAM, and don't pay just for big numbers, pay for the right features.