BigTable white paper

[Staz]

I've seen a few questions about BigTable in comparison to relational
databases here. Its worth pointing out that BigTable isn't a "cut
down" relational database that lacks some features that other RDBs
have, its a completely different type of database. It is designed for
massive scalability, and so does some things very differently.

There's a great description of how it works at http://labs.google.com/papers/bigtable.html