The Raspberry Pi primarily uses Unix-like Linux-kernel-based operating systems, such as variants of Debian and Fedora.
Raspberry Pi Models A, A+, B, and B+ are based on the ARM11 family chip, which runs on the ARMv6 instruction set. The ARMv6 instruction set does not support Ubuntu and Windows.
However, the recently launched Raspberry Pi 2 is based on ARM Cortex A7, which is capable of running Windows 10 and Ubuntu (Snappy Core). The following operating systems are officially supported by all the models of Raspberry Pi and are available for download at the download page:
Windows 10 and Ubuntu are only supported by ...