NVIDIA offers several Tegra development kits. From this page, you can find specifications, OS images and tools relevant to each development kit. If you have questions or issues, please check the Tegra Forums as others might have hit the same issue as you.
Hardware Inquiries
If you are looking to evaluate Tegra for a hardware project, please check the Tegra Hardware & Sales Inquiries page. The Tegra development kits are targeted at software developers. NVIDIA does not offer chip specifications, data sheets, pin-out information or other low-level hardware information with these kits or through this website.
Development Kits
Registered Developers Website
NVDeveloper (old site)