Most personal computers come without a network adapter installed because there are so many choices.
Ethernet also comes in less popular bus styles, using coaxial cable to interconnect the computers at 10 Mbps. 10BaseT wiring and 10Base2 coax must be installed specifically for data networking. The advantage of these types of networks is that new wiring may be avoided that will save a significant amount of expense and time to install. Moreover, installed wiring in the small office is a type of leasehold improvement that is usually at the lessee's expense and no compensation is given when the lease expires or the lessee moves to other quarters. Wired networks can usually pay for themselves if used for three or more years.