Internet history can be found at InternetValley Archives link and CERN link Most websites have lives of 1 months to 2-6 years. The Internet Archive accomplishes a full archive of the Internet with Alexa Internet Alexa link robots every 2 months, at off hours, respecting bandwidth and user prime time activity. The Internet Archive presently holds 42 TB of information on disk arrays. Tape has proven unreliable. Simply put, the Internet, host server and marked-up content work together to assemble the site on a user's computer.
Websites are cultural entities.
If website content, structure and appearance are not saved and documented, they will be lost. While not all websites require preservation, there are specific significant cultural sites which we need to learn to save effectively. A cached website will save content that has been accessed by a user, but not all parts of a site are commonly accesses by a user, so not all of a site's appearance is saved in a cache. Caching, also, does not save a site's functionality. Searching caches will find some lost information, but it can not relied upon for preservation.