For targeting various embedded use-cases, Jan Altenberg of Linutronix presented how to achieve this feat of booting Linux in under one second.
Booting Linux in one second can be useful for automotive applications -- among other scenarios -- greater energy savings rather than dealing with suspending the system, and more. Some of the work done by Linutronix -- a German company focused on Linux for industrial use-cases -- included optimizations to the U-Boot boot-loader, using LZO kernel image compression, various kernel command-line tweaks, kernel configuration changes, using UbiFS, and more.
Using an Atmel AT91 ARM9 SoC with Angstrom Linux and NAND flash storage, the stock boot time began at 11 seconds but with simple optimizations dropped to 8 seconds and then with the extensive modifications in time dropped to around 656 ms.
More details can be found via the PDF slides and the video presentation from Embedded Linux Conference Dublin that's embedded below.