You can use this search tool two ways. One as a quick search if you know the Filename of the file you're requesting. Or two if you want to do a more general search.
Entering a filename only into this search tool will quickly locate the file and display all the products that are associated with that file. When using the tool like this only input the Filename leave all the other options alone. Unlike a web search engine like "Google", the input used is queried for exact matches. So a search for s3g03_0 will find the switch 4900 software. The more information you give the finer your search. If your search is not successful try reducing the input to produce more results.
Use the pull downs to locate files by type or category. These searches will return a large amount of data and should only be used when you are browsing for product software.