[To expand a bit on one of techie's comments, 100m is a hard limit for a half-duplex link. This is because of the "slot time" built into the Ethernet retransmission algorithm. If you make the length longer than that, you will have collisions that aren't detected, resulting in lost packets.
Ethernet can run up to 500m on a half-duplex link (thick coax). There is a limit for the total network diameter to ensure that collisions are still detected, but there's no way you're going to exceed it with a single twisted pair link.
I note that normally hubs are half-duplex, and switches are full-duplex.
Hubs are always half-duplex. Switches can be either half or full duplex according to either the port settings or autonegotiation. One of the most annoying problems I've encountered is admins forcing the ports to full-duplex which breaks autonegotation. The end result of this is terrible performance unless you set the network card in the PC to also run in full-duplex.
Unmanaged switches will not allow you to change the port duplex settings manually. They are autonegotiation-only.
