Hardware Reference
In-Depth Information
As you can see, displaying 32-bit color (4,294,967,296 colors) at 1920×1080 resolution requires just
short of 8MiB of RAM on the video adapter. Because most modern video cards have at least 512MiB
or more, you can see that two-dimensional images don't require much memory.
3D video cards require more memory for a given resolution and color depth because the video
memory must be used for three buffers: the front buffer, back buffer, and Z-buffer. The amount of
video memory required for a particular operation varies according to the settings used for the color
depth and Z-buffer. Triple buffering allocates more memory for 3D textures than double buffering but
can slow down the performance of some games. You can usually adjust the buffering mode used by a
given 3D video card through its properties sheet.
Note
As we discuss 3D in this and following sections, we are referring to the rendering of 3D
graphics on your display. 3D display technologies (which involve special glasses and 120MHz
or greater refresh rates on LCD or LED backlit displays) are a different issue.
Although current chipset-integrated graphics solutions feature 3D support, the performance they offer
is limited by being based on older, less powerful 3D GPUs and by the narrow data bus they use to
access memory. Because integrated graphics solutions share video memory with the processor, they
use the same data bus as the processor. In a single-channel-based system, this restricts the data bus to
64 bits. A dual-channel system has a 128-bit data bus, but today's fastest 3D video cards feature a
512-bit or wider data bus. The wider the data bus, the more quickly graphics data can be transferred.
For these reasons, you are likely to be disappointed (and lose a lot of games!) if you play 3D games
using integrated graphics. To enjoy 3D games, opt for a mid-range to high-end 3D video card based
on a current AMD or NVIDIA chipset with 1GB of RAM or more. If you demand peak performance
and your budget permits, you might also consider using a multicard solution that allows you to use
two or more PCIe video cards to increase your graphics processing performance.
See the section, “
Dual-GPU Scene Rendering
,”
p.
648
.
Note
If your system uses integrated graphics and you have less than 2GB of RAM, you might be able
to increase your available graphics memory by upgrading system memory (system memory is
used by the integrated chipset). Some chipsets with integrated graphics automatically detect
additional system memory and adjust the size of graphics memory automatically.
Video Memory Bus Width
Another issue with respect to the memory on the video adapter is the width of the bus connecting the
graphics chipset and memory on the adapter. The chipset is usually a single large chip on the card that
contains virtually all the adapter's functions. It is wired directly to the memory on the adapter through
a local bus on the card. Most of the high-end adapters use an internal memory bus that is up to 512
bits wide (or more in some cases). This jargon can be confusing because video adapters that take the
form of separate expansion cards also plug into the main system bus, which has its own speed rating.
When you read about a 256-bit, 384-bit, or 512-bit video adapter, you must understand that this refers
to the memory connection on the card, not the connection to the motherboard. In two cards with
