PlayStation 4 reserves 3.5GB of its 8GB GDDR5 memory for the operating system, leaving 4.5GB of space for game code, according to current PlayStation 4 documentation shown to Digital Foundry by a well-placed development source. However, further sources suggest that an additional 1GB of "flexible memory" may be reclaimed from the OS reservation, based on availability.
Sony's internal docs say that 4.5GB is the baseline amount of guaranteed memory available for game-makers (note the memory usage of the Killzone: Shadow Fall demo) and most likely what the lion's share of launch titles will be using. However, other sources close to Sony indicate that developers can request up to an additional gigabyte of "flexible memory", and use it to boost elements of the game - but only if the background OS can spare it. We're told that incorporating this isn't trivial, and it may well be that to begin with only first-party developers target its usage.
The news that the PS4's OS reservation is in the same ballpark as Xbox One's equivalent 3GB allocation is sure to surprise many, especially bearing in mind that previously leaked Sony docs have only spoken of a 512MB allocation for the system software - though this information hails from the era where the new PlayStation was slated to ship with only 4GB of memory.
