When would a company want to use each?
Good questions. A reader chip is an integrated microchip that takes some of the discreet components on the circuit board of an RFID reader and combines them into a single device. It is the brains of a reader, analogous to the CPU in a desktop or laptop computer. The reader (or interrogator) is a device that contains the reader chip (or discreet reader components on a printed circuit board), a network connection, a power connection and antenna ports. A reader can have internal or external antennas that emit radio waves and receive them back from a transponder.
When people use the term "RFID reader," they typically mean the complete device with antennas. If you want to communicate with a transponder—that is, interrogate the information it contains or write data to it—you need a reader with a reader chip in it (or the components contained therein on a printed circuit board) and an antenna.
—Mark Roberti, Founder and Editor, RFID Journal