Functionally, W5100S is very similar to W5100 and W5500, with slightly different Hardware Specification. And Software can be shared. For example, Software written for the W5100 or W5500 is compatible with Hardware for the W5100S. However, there are some differences between W5100S and W5100/W5500 have in Software and Hardware. The difference are described in the document titled "W5100S comparison sheet" below.