Published at LXer:

The operating system at the heart of Sony's PlayStation 4 is FreeBSD 9.0. It's been exposed that the operating system powering the PlayStation 4 is Orbis OS, which is a Sony spin of FreeBSD 9.0. It's not a huge surprise FreeBSD is being used over Linux, in part due to the more liberal licensing. The PlayStation 4 is x86_64 based now rather than Cell-based, which makes it easier to use FreeBSD.

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Why ? Because of what happened with Linux on the PS3.

Would you elaborate on that a bit, TeXMeX? What are you referring to about the PS3 in particular?

I know that up through a certain firmware level Sony allowed an "Other OS" (Linux) to be loaded on the PS3. Linux distributions that supported the Cell processor (PowerPC architecture) could be installed. I ran YDL on my PS3 for a while, and I believe Fedora and Debian had working ports. IBM's Cell SDK and OpenCL could be used to facilitate cluster computing of multiple PS3 systems to create low-cost mini-supercomputers. Then suddenly Sony dropped "Other OS" support citing security concerns.

If the PS4 is X86-64 based, perhaps it will be possible to run bog-standard Linux distros.

The PS2 and the PS3 already used parts of the BSD systems, since the PS4 is x86_64 it is only a logical step to customize one of the BSDs as OS for the PS4. Since it is running on AMD hardware it even may have a nice effect for the BSDs, the possibility of getting the Catalyst driver for those OSes.

Regarding running Linux on that machine, you can be pretty sure that Sony uses Secure Boot or a similar mechanism so that only signed software can run on it.

They dropped "Other OS" because it could be used to root the system ... and it was rooted.

I'll bet you anything you will not get an "Other OS" option on the PS4 or any future PS*.