The first generation of Fabric OS was developed on top of a VxWorkskernel and was mainly used in the Brocade Silkworm 2000 and first 3000 series on Intel i960. Even today, many production environments are still running the older generation Silkworm models.
Second generation
The second generation of Fabric OS was developed on a PowerPC platform, and uses MontaVistaLinux, a Linux derivative with real-time performance enhancements. With the advent of MontaVista, switches and directors have the ability of hot firmware activation (without downtime for Fibre Channel fabric), and many useful diagnostic commands.
According to free software licenses terms, Brocade provides access to sources of distributed free software, on which Fabric OS and other Brocade's software products are based.