100baseTX runs over two pairs of wires in category-5 cable. Like 10BASE-T, the proper pairs are the orange and green pairs (canonical second and third pairs) in the TIA-568B wiring standard.
In TIA-568B, wires are in the order 1, 2, 3, 6, 5, 4, 7, 8 on the modular jack on each end. The colour-order would be orange/white, orange, green/white, blue, blue/white, green, brown/white, brown.
Each segment can have a maximum distance of 100 metres. Capable of 100 Mbit/s throughput. See IEEE 802.3 for more details.
The configuration of 100BASE-TX networks is very similar to 10BASE-T. When used to build a local area network, the devices on the network (computers, printers etc.) are typically connected to a hub or switch, creating a star network. Alternatively it is possible to connect two devices directly using a cross-over cable.
See also
Based on material from FOLDOC, used with permission.