FTDI has evolved two types of driver for its ICs: VCP and D2XX. The VCP driver makes the device appear in the system as a serial port. Applications access the port using the Win32 COMM API as if it was a normal serial port. The driver consists of two layers: FTDIBUS and FTSER2K. FTDIBUS handles the creation of the serial port and access to the hardware and FTSER2K is the implementation of the serial port. These drivers communicate using the FTDIBUS class interface.
The D2XX driver is used in situations where a serial port is not required. It allows access to the device via the proprietary D2XX API. The driver is implemented as a single layer, FTD2XX.SYS, and is normally accessed through the library FTD2XX.DLL.