Timothy Lottes has provided a comparison between the 4 GB of GDDR5 RAM being used for the PS4 to the 8 GB of DDR3 RAM, along with an additional 32 MB of ESRAM, powering the Xbox 720. As spotted in the comments section of his blog on Jan. 26, the creator of the FXAA believed that developers will prefer the RAM configuration of the PS4 over the setup of the Xbox 720. Due to the limitations of the 32 MB ESRAM, the same next-generation video games may be rendered at 30 frames per second with a 720p resolution on Microsoft’s next-console as opposed to the same frames per second (although some could also reach 60) at 1080p resolution for Sony’s upcoming system. You can check out some concept designs of the PS4 and Xbox 720 in the slideshow at the top of this article and the comments from Timothy Lottes below (courtesy of the Timothy Lottes Blog):
A fast GDDR5 will be the desired option for developers. All the interesting cases for good anti-aliasing require a large amount of bandwidth and RAM. A tiny 32MB chunk of ESRAM will not fit that need even for forward rendering at 1080p. I think some developers could hit 1080p@60fps with the rumored Orbis specs even with good AA. My personal project is targeting 1080p@60fps with great AA on a 560ti which is a little slower than the rumored Orbis specs. There is no way my engine would hit that target on the rumored 720 specs. Ultimately on Orbis I guess devs target 1080p/30fps (with some motion blur) and leverage the lower latency OS stack and scan out at 60fps (double scan frames) to provide a really great lower-latency experience. Maybe the same title on 720 would render at 720p/30fps, and maybe Microsoft is dedicating a few CPU hardware threads to the GPU driver stack to remove the latency problem (assuming this is a "Windows" OS under the covers).
The PS4 and Xbox 720 will reportedly be released sometime during late 2013. The rumored specs for the two next-generation systems from Sony and Microsoft are very similar with the exception of the aforementioned RAM configurations.