Originally Posted by Digital Foundry
As it stands, both next-gen consoles will launch with 8GB of unified memory, but with a significantly diminished amount actually available to games developers. However, a big area of difference between Sony and Microsoft's approaches to OS allocation could come in their future plans for the reserved RAM. A Microsoft insider tells us that the engineers behind the Xbox One specifically chose 3GB in order to allow the background platform to evolve over a ten-year life-cycle - it's very hard to add features if the pool of available RAM is reduced from its initial level. The reserved RAM allocation there is set in stone, and is unlikely to change.
However, sources close to Sony suggest that the PS4 approach is perhaps more flexible - the current allocation in terms of both CPU cores and memory could be reduced once the operating system is complete and then streamlined. In short, while there is no guarantee of change in the future, Sony is at least leaving the door open to the opportunity and the R&D team has experience in reducing the OS footprint - just as it did on PlayStation 3.