Even Intel, the company that makes most of the computer processors used in PCs, has such a device. Things that connect two Windows PCs together are likely to be useless when you want to add a different kind of computer to your home or small-office network. You need Ethernet for that. Ethernet comes in two basic speeds. The most common operates at 10 megabits per second and the other works at 100 megabits per second.
Megabits is a confusing word, since it sounds like megabytes.
A bit is one-eighth of a byte, and in most cases two extra bits are tacked onto those eight bits when they're sent somewhere. Faster Ethernet methods are available, too, but they cost too much for most homes and small offices.