"If you look at the number of lines changed, we've had bigger releases in the past, but they have tended to be due to specific issues. In contrast, 4.9 is just big."
Additions include support for the tiny $5 Raspberry Pi Zero machine and the LG Nexus 5, alongside 27 other ARM-based boards, and experimental support for older AMD graphics cards. These cards are based on AMD's Graphics Core Next 1.0 architecture, such as the Radeon HD 7000 Series.
The release also incorporates the Greybus driver subsystem, which is based on work undertaken as part of Google's now abandoned Project Ara to develop a modular smartphone. During Ara, Google engineers developed the Greybus hardware protocol, which provides an application layer for UniPro, a high-speed interface for connecting circuits in mobile devices. The UniPro bus was chosen as being a good fit for a phone where electronic components such as cameras, speakers and displays could be swapped out at will.
Other improvements include better stability and security thanks to support for Intel Memory Protection Keys and vmapped kernel stacks, improved support for P-State power-saving features on some Intel Atom processors and the ability to use virtual displays on AMD GPUs.