In storage area networking, Fabric OS (FOS) is the firmware for Brocade Communications Systems's Fibre Channel switches and Fibre Channel directors.
[1] The first generation of Fabric OS was developed on top of a VxWorks kernel and was mainly used in the Brocade Silkworm 2000 and first 3000 series on Intel i960.
The second generation of Fabric OS (4.0) was developed on a PowerPC platform, and uses MontaVista Linux, 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.
Additional products for Fabric OS are offered by Brocade for one-time fee.