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-200 consists of the following components: reduced instruction set computing (RISC) microprocessor. The NPE-200 has an R5000 microprocessor that operates at an internal clock speed of 200 megahertz (MHz); system controller that uses direct memory access (DMA) to transfer data between DRAM and packet SRAM on the network processing engine; DRAM for storing routing tables, protocols, network accounting applications, packets of information in preparation for process switching, and packet buffering for SRAM overflow. The standard configuration is 32 MB, with up to 128 MB available through single in-line memory modules (SIMM) upgrades; packet SRAM for storing packets of information in preparation for fast switching. The NPE-200 has 4 MB of SRAM; unified cache SRAM that functions as the secondary cache for the microprocessor; (The primary cache is within the processor.) two environmental sensors for monitoring the cooling air as it leaves the chassis; Erasable programmable read-only memory (EPROM) for storing sufficient code for booting the Cisco IOS software.