[question] speed

[Traut]

Hi all

   I'm working on some presentation for my co-workers about Lucene/Solr 
index/search process. The question is why lucene (especially Solr) is 
such a fast engine?

Has it something to do with index file formats 
(http://lucene.apache.org/java/docs/fileformats.html)?

or is it all about using reverse indexing strategy?

I'm have been digging into Lucene/Solr for nearly three month but only 
as an advanced user so I am not familiar with the details of engine 
implementation

thank you

Traut