Hardware Reference
In-Depth Information
Some of the newer cards use GDDR4 SGRAM. Compared to GDDR3, GDDR4 memory has the
following features:
• Higher bandwidth. GDDR4 running at half the speed of GDDR3 provides comparable
bandwidth to its predecessor.
• Greater memory density, enabling fewer chips to be needed to reach a particular memory size.
GDDR5 SGRAM
GDDR5 SGRAM is based on the previous GDDR standards with several modifications to allow
increased performance. The main differences include the following:
• Signal optimization using data/address bit inversion, adjustable driver strength, adjustable
voltage, and adjustable termination
• Adaptive interface timing using data training that is scalable per bit or byte
• Error compensation, including real-time error detection on both read/write and fast resending
GDDR5 is also designed for extreme power management such that power is used only when
necessary. This allows higher clock speeds with cooler operation. Current GDDR5 parts are rated up
to 7Gbps per chip, allowing 28GBps total bandwidth.
Video RAM Speed
Video RAM speed is typically measured in MHz, GHz, or by bandwidth in Mb/Gb or MB/GB per
second. Faster memory and faster GPUs produce better gaming performance, but at a higher cost.
However, if you are primarily concerned about business or productivity application performance, you
can save money by using a video card with a slower GPU and slower memory.
Unless you dig deeply into the technical details of a particular graphics card, determining what type
of memory a particular card uses can be difficult. Because none of today's video cards feature user-
upgradeable memory, I recommend that you look at the performance of a given card and choose the
card with the performance, features, and price that's right for you.
RAM Calculations
The amount of memory a video adapter needs to display a particular resolution and color depth is
based on a mathematical equation. A location must be present in the adapter's memory array to
display every pixel on the screen, and the resolution determines the number of total pixels. For
example, a screen resolution of 1920×1080 requires a total of 2,073,600 pixels.
If you were to display that resolution with only two colors, you would need only 1 bit of memory
space to represent each pixel. If the bit has a value of 0, the dot is black, and if its value is 1, the dot
is white. If you use 32 bits of memory space to control each pixel, you can display more than 4 billion
colors because 4,294,967,296 combinations are possible with a 32-digit binary number (2
32
=
4,294,967,296). If you multiply the number of pixels necessary for the screen resolution by the
number of bits required to represent each pixel, you have the amount of memory the adapter needs to
display that resolution. Here is how the calculation works:
