Sony's lead system architect and hardware wizard Mark Cerny, has delved into the innards of PS4 as well as PlayGo which allows users to download games and start playing them before the download is finished.
According to Cerny, with PlayGo, PS4 owners will only have to download part of the game's data in order to the play it. The rest of the title will continue to install on your system as PS4 copies data from the Blu-ray disc onto your hard drive. PlayGo is basically "two separate linked systems."
“The concept is you download just a portion of the overall data and start your play session, and you continue your play session as the rest downloads in the background," Cerny told Gamasutra.
"So, what we do as the game accesses the Blu-ray disc, is we take any data that was accessed and we put it on the hard drive. And if then if there is idle time, we go ahead and copy the remaining data to the hard drive. And what that means is after an hour or two, the game is on the hard drive, and you have access, you have dramatically quicker loading... And you have the ability to do some truly high-speed streaming."
The system also supports zlib decompression which will allow developers to compress game data which will them be decoded by PS4 automatically.
Background downloads are also handled by a second custom chip which puts PS4 into low-power mode, making it more "green."
"We have the ability to turn off the main power in the system and just have power to that secondary custom chip, system memory, and I/O -- hard drive, Ethernet," Cerny explained.
"So that allows background downloads to happen in a very low power scenario. We also have the ability to shut off everything except power to the RAMs, which is how we leave your game session suspended."
It's a rather interesting read, so you should really head through the link. In it, Cerny also says PS4 will have a "stronger line-up than any prior PlayStation hardware."
He doesn't go into detail on it though, as he can't divulge the number of launch titles, so just take his word for it I reckon.