Flexible PIC Concentrators (FPCs) house the PICs that connect the router to network media (for information about PICs, see Physical Interface Cards (PICs)). On the M5 and M10 routers, each FPC is built in (cannot be removed from the chassis as on other M-series platforms) and corresponds to a horizontal row of PIC slots. The single FPC on the M5 router is numbered 0 (zero) and the two FPCs on the M10 router are numbered 0 and 1, top to bottom. Each FPC accommodates up to four regular PICs or one quad-wide PIC.