Canonical has been working hard on boot times. The Ubuntu 9.04 release that came out in April already brought improvements in that area, but as Ars Technica reports, the Ubuntu team isn't done. Apparently, the latest alpha release of Ubuntu 9.10 can boot in as little as five seconds on some configurations.
Ars says Canonical Developer Relations Coordinator Jorge Castro recorded that impressive boot time on his own computer, which has a 2.4GHz Core 2 Duo processor and a solid-state drive. He has a boot chart to prove it, too. The Ubuntu team added some special sauce to speed up SSD boot times in particular, as Ars explains:
One of the most significant technical factors contributing to awesome SSD boot performance is the inclusion of sreadahead, a system service that uses prefetching to load data that is used by the boot process before it is needed. It will also cache the prefetched data and store it so that it can be used during subsequent boots, but it's less effective on conventional hard disks where seek latency introduces some challenges. Ubuntu developer Scott James Remnant explained some of the technical nuances in a mailing list post a few months ago.
Users of mechanical hard drives can still look forward to improvements, albeit none as dramatic. Ars recorded an average 22-second boot time on a two-year-old Dell Inspiron 1420n notebook.
You can try Ubuntu Linux 9.10 alpha 6 for yourself by grabbing the installation image here. Naturally, since this is alpha software, we'd recommend against installing it on a production system.