The network processing engine maintains and executes the system management functions for Cisco 7200 series routers. The network processing engine also shares the system memory and environmental monitoring function with the I/O controller. The NPE-175 has an RM5270 microprocessor that operates at an internal clock speed of 200 MHz. The NPE-175 and NPE-225 have one system controller that provides processor access to the two midplane and single I/O controller PCI buses. The system controller also allows the port adapters on either of the two midplane PCI buses to access SDRAM. The NPE-175 and NPE-225 use SDRAM for providing code, data, and packet storage. The NPE-175 and NPE-225 have two levels of cache: a primary cache that is internal to the processor and a secondary, 2-MB external cache that provides additional high-speed storage for data and instructions.