Both switches and routers do "things" in both software and hardware. Generally, switches do "more" in hardware (but often with "less" function). Data plane functions are more likely to be done in hardware while control plane functions are more likely done in software. (Reasons for the data plane and control plane "split", control plane function often more complex but "less" volume.)
Anyway, what's done in hardware or software depends on the specific switch and/or router. Later model Cisco routers continue to provide more functions (including possibly QoS functions) with dedicated hardware support.
