SQL Server 2008 Brochure is available to download. It contains many information like available Server Editions, Top New Features, New Available Technologies and additional resources.
Just a day ago, while I was surfing Wikipedia about SQL Server, I came across this generic architecture image. I found it interesting. Click on image to view it in large size. The physical structure of the database is divided into the MDF and LDF. The part of MDF contains file group, data files, tables and indexes, extended and page. The LDF file contains a transaction log file. The physical architecture is about how the data is actually stored in the file system. Page, extend, database files are physical architecture.