The Powerbook G3 G4 MApple Modem Card U01.025.C.00 is a 56K internal modem card designed for use with iMac and Powerbook G3 M5521 computers. This modem card, made by Apple, is compatible with Apple brand devices and offers a maximum data rate of 56 KBps. With a compact size of 3 inches in length and 2.25 inches in width, this modem card is an essential component for connecting to the internet at a faster pace on older Apple devices.