GDDR3, Graphics Double Data Rate 3, is a graphics card-specific memory technology, designed by ATI Technologies with the collaboration of JEDEC.
It has much the same technological base as DDR2, but the power and heat dispersal requirements have been reduced somewhat, allowing for higher-speed memory modules, and simplified cooling systems. Unlike the DDR2 used on graphics cards, GDDR3 is unrelated to the JEDEC DDR3 specification. This memory uses internal terminators, enabling it to better handle certain graphics demands. To improve bandwidth, GDDR3 memory transfers 4 bits of data per pin in 2 clock cycles.
The GDDR3 Interface transfers two 32 bit wide data words per clock cycle from the I/O pins. Corresponding to the 4n-pre fetch a single write or read access consists of a 128 bit wide, one-clock-cycle data transfer at the internal memory core and four corresponding 32 bit wide, one-half-clock-cycle data transfers at the I/O Pins. Single-ended unidirectional Read and Write Data strobes are transmitted simultaneously with Read and Write data respectively in order to capture data properly at the receivers of both the Graphics SDRAM and the controller. Data strobes are organized per byte of the 32 bit wide interface.
Despite being designed by ATI
, the first card to use the technology was nVidia
's GeForce FX
5700 Ultra, where it replaced the GDDR2 chips used up to that time. The next card to use GDDR3 was nVidia's GeForce 6800 Ultra
, where it was key in maintaining reasonable power requirements compared to the card's predecessor, the GeForce 5950 Ultra
. ATI began using the memory on its Radeon X800
cards. GDDR3 was Sony
's choice for the PlayStation 3
gaming console's graphics processor, although its nVidia
based GPU is also capable of accessing the main system memory which is comprised of XDR DRAM
designed by Rambus Incorporated
(Similar technology is marketed by nVidia as TurboCache in PC platform GPUs). Microsoft
's Xbox 360
is shipped with 512 MiB
of GDDR3 memory, and is helping to pioneer the use of this memory as standard system memory rather than only video memory. Nintendo
also contains GDDR3 memory.
Advantages of GDDR3
- GDDR3s strobe signal unlike GDDR2 is Uni Directional & Single-ended (RDQS, WDQS). This means there is a separate read and write data strobe allowing for a quicker read to write ratio than GDDR2.
- GDDR3 has a hardware reset capability allowing it to flush all data from memory and then start again.
- Lower voltage requirements leads to lower power requirements.
- Higher clock frequencies.