The PS4 doesn't give developers access to a whole lot of memory
Brand new report has appeared online citing technical documents from Sony, which say that developers can use just 4.5GB of the PlayStation 4's total of 8GB of RAM, although that can be extended to around 5.5GB, but only in certain cases.Both the PlayStation 4 and the Xbox One are bragging about their 8GB of RAM, either in the form of GDDR5 tech, when talking about the PS4, or DDR3, when considering the Xbox One.
Sadly, neither of the consoles allow developers to use those 8GB, as considerable portions are reserved for the operating systems.
After hearing that the Xbox One's OS occupies 3GB, it seems that the PS4's system occupies anywhere between 2.5 and 3.5GB.
According to Digital Foundry, developers can have access to 4.5GB of RAM in a normal setting but that can be extended to 5.5GB, in certain cases.
The report cites technical documents sent by Sony to developers and makes no mention of other restrictions.