Well, we know the PS3 has 6 SPUs available to developers with one reserved for the OS (i.e., security) and one disabled, right? I remembered that it seemed like GG had a PDF that showed Killzone 2 only using 4 SPUs, and I decided to dig it up.
http://www.guerrilla-games.com/publications/dr_kz2_rsx_dev07.pdf
Starts on page 45, shows usage for 4 SPUs and the PPU. What are the other two doing? Dunno. Game AI and Physics are shown to be on the PPU. There's definitely audio happening somewhere in there, but I'd be surprised if it took both SPUs unless it's something like encoding DTS 7.1. Even the Edge tools Cell geometry acceleration is accounted for, unless "edgeGeom" is something else.
So no, we can't assume there's two cores reserved for the OS because a Guerrilla Games PDF doesn't show usage for two of the cores.
http://www.guerrilla-games.com/publications/dr_kz2_rsx_dev07.pdf
Starts on page 45, shows usage for 4 SPUs and the PPU. What are the other two doing? Dunno. Game AI and Physics are shown to be on the PPU. There's definitely audio happening somewhere in there, but I'd be surprised if it took both SPUs unless it's something like encoding DTS 7.1. Even the Edge tools Cell geometry acceleration is accounted for, unless "edgeGeom" is something else.
So no, we can't assume there's two cores reserved for the OS because a Guerrilla Games PDF doesn't show usage for two of the cores.