It's only rumor which i doubt is true, from what i've read it seems they've sent out dev kits with only 1gb for the OS and the rest is for games, so it wouldn't make sence for them to change it now
It hasn't been confirmed by Sony. But 4.5gb is what the developers kits aim for as far as usage. There is a normal mode, and a large mode during development. The normal uses up to 4.5gb or ram and the large mode uses 5.25. Somebody, I don't know if it is Sony has said they might be able to get the PS4 to release some of the OS ram for 5.5gb. But 4GB is a allot for a game.
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