At first look, routers look like a PC. They have a CPU, memory, and, on the back, ports and interfaces to catch up peripherals and different communications media. They sometimes even have a monitor to provide as a system console.

But there is one important difference from a PC: routers are diskless. They do not even have floppy disks. A router exists to do just that route. They don’t live to make or display information or to store it, even temporarily. Routers have as their only task of filtering incoming packets and routing them outbound to their proper destinations.

The other variation is the type of add-on modules that can be plugged into routers. Whereas typical PC has cards for video, sound, graphics, or other purposes, the modules put into routers are severely for networking. These are called interface modules, or interfaces. When people or documents refer to a router interface, they mean an actual, physical printed circuit board that holds a particular networking protocol. EO and E1, possibly mean Ethernet interface numbers 1 and 2 inside a router. Interface modules are always layer-2 protocol particular. There is one protocol per interface.

Interfaces are included according to network environment in which they will work. E.g. a router might be organized with interface modules only for Ethernet. A router serving in a mixed-LAN environment, by contrast, would have interfaces for both Ethernet and Token Ring protocols, and if that router were acting as a LAN-to-WAN moment, it might also have an ISDN module.

There is one last dissimilarity between routers and general-purpose PCs a slighter one. PC product lines are about always based on common CPU architecture, E.g. Wintel PCs on venerable Intel x86 architecture, Apple’s Motorola 68000 variants, Sun’s SPARC, and so on.

Cisco routers utilize a range of CPUs, each selected to fit a particular mis- sion. Cisco SOHO 70 Series routers, e.g. use 50 MHz CPUs. Cisco possibly made this collection because 70 Series is intended for small office or home office use, where activity loads are light. The Motorola MPC 855T RISC chip is dependable; able of handling job; and, maybe most important, inexpensive. Moving up router product line, Cisco uses increasingly more powerful general-purpose processors from Motorola, Silicon Graphics, and other chip makers.