This is follow up question to @martin smith excellent answer https://stackoverflow.com/questions/1251636/what-do-clustered-and-non-clustered-index-actually-mean
After that i have watched MCM video of Paul randal which shows why index fragmentation matters more in large scans only for huge tables..If i understood correctly, external/logical fragmentation occurs when logical continuity of pages differ from physical order in which they should be..
Suppose i have big table and identity as clustered key and no updates to clustered key and all pages are in logical order,does Sql guarantee all these pages lay in disk in close proximity...during first inserts it may block some space for this table,but after that many inserts may happen to other tables as well,so data might not be in close proximity...Is my understanding correct ?