Most of the Discrete graphics chips or the graphics cards come either with DDR3 memory of the GDDR5 memory. The GDDR5 memory is faster than the DDR3 and the difference can be as high as 2x ( per pin) depending upon the speed grade of the DDR3 and the GDDR5 memory compared.
The graph ( courtsey Elpida) , shows an approximate comparison of the DDR3 and the GDDR5 memory speed.
Typically using a GDDR5 memory in place of DDR3 memory can lead to 15% improvement in the performance with respect to the DDR3 memory.
The Power Consumption
GDDR5 memory is a able to provide the performance improvement without any significant improvement in the power consumption.
Dynamic Frequency and Voltage Scaling
Most of the GDDR5 memories support the Dynamic Frequency and Voltage Scaling not available in the DDR3. This allows the dynamic scaling of the performance versus the power consumption.
The GDDR5 memory comes in speed grade upto 6 Gbps, with 7 Gbps speed grade are also being planned by some manufacturers.
The DDR3 memory is designed with two factors in mind
1. It should be possible to allow higher amount of memory to allow many chips ganged together. This reduces the maximum speed possible.
2. The data packet sizes can be smaller. The GDDR5 memory on the other support data access granularity of 256 bits.
The Following table captures the Key difference between the DDR3 and GDDR5
Table 1 : DDR3 Vs GDDR5
|Max Data rate per pin
||1866 Mbps||6.0 Gbps|
|IO Width||4, 8, 16||16, 32|
|Data Granularity||64 / 128 bits||256 bits|