IFS is the File system to talk to your business network.
According to IBM “The IFS integrated file system is a part of the IBM® i operating system that supports stream input/output and storage management similar to personal computer and UNIX operating systems, while providing you with an integrating structure over all information stored in the system.”
For many years the IBM i operating system (the replacement for OS400 on both the AS400 and iSeries) supports other file systems apart from QSYS.
The IFS is a PC-type file system, a Unix-style file system, QDLS (shared folders – but has now been retired) and even the equivalent of Network Neighbourhood!
These other file systems will become more important as you start to explore the new functionality of the system. How about being able to maintain a HTML document in an RPG program or (as of V5R2) storing your RPG source in directories in the root file system as opposed to source physical files? This is coming in the next release of IBM i.