"Memory controller compatibility with GDDR5 and DDR3."
- http://www.rambus.com/ass...2_memory_architecture.pdf
Which could explain why Sony is going for GDDR5 and Microsoft is going for DDR3.

Sony Sticks to Industry-Standard GDDR5, Throws XDR Away from PS4
[02/20/2013 11:52 PM]
After two generations of PlayStation game consoles relied on high-speed memory designed by Rambus, Sony Computer Entertainment has decided not to use proprietary memory types inside its next-generation PlayStation 4 video game system that will feature-industry-standard GDDR5 random access memory.
In a bit to create memory sub-system with unprecedented performance and 3.20GB/s throughput, Sony started to use dual-channel 32MB of RDRAM memory designed by Rambus in its PlayStation 2 game console back in the year 2000. Since Cell processor only supported XDR DRAM, Sony also had to use 256MB of exotic 3.20GHz XDR memory developed by Rambus in its PlayStation 3 in 2006.
Thanks to adoption of custom AMD Fusion system-on-chip with eight Jaguar x86 cores and specialized Radeon HD graphics processor, the PlayStation 4 now relies on 8GB of industry-standard GDDR5, which Sony can source from three manufacturers (Samsung, Micron/Elpida and SK Hynix), instead of two (Samsung, Micron/Elpida). Usage of GDDR5 will positively affect costs of the new-generation console since unlike the XDR the GDDR5 is manufactured in high volumes and is used on add-on graphics adapters for desktop and notebook personal computers and is therefore much more cost-efficient.
Sony PlayStation 4 multi-channel memory sub-system will feature peak bandwidth of 176GB/s, a little higher compared to that of the Radeon HD 7870 (153.6GB/s on 256-bit GDDR5 at 4.80GHz) graphics card, and significantly higher compared to rumoured 68GB/s bandwidth offered by Xbox Next main DDR3-based memory sub-system as well as graphics-dedicated ESRAM with 102.4GB/s throughput.
Despite of the fact that Sony abandoned Rambus memory from its forthcoming consoles, it does not mean that the company will cease to use XDR completely. The company will continue to sell XDR-based PlayStation 3 systems for a while and it is nearly guaranteed that tens of millions of game consoles will be sold over the next years. Besides, since Sony will offer PS4 owners to stream games developed for the previous-generation systems from the cloud, the company will have to create servers featuring PS3 hardware to run appropriate games in data centers. Quite likely that Sony will have to install Cell processors along with 256MB of XDR memory into such machines.
Tags: Sony, Playstation, Rambus, XDR, GDDR, RDRAM, Samsung, Elpida, Micron, Hynix
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