FTDI has 2 primary drivers: the VCP and D2XX. VCP (FTSer2k.SYS) causes the USB device to appear as an additional COM port available to the PC. Application software can access the USB device in the same way as it would access a standard COM port. This is a custom driver that needs to be loaded with FTDI devices. The driver has an auto-baud feature that automatically sets the baud rate of the device as per the application request during initialization of a USB COM port. The driver provides all the necessary signals for implementing an RS232 9-pin interface, including the complete set of handshaking signals. Using VCP drivers, the applications can achieve a 3M baud rate at TTL logic levels. An RS232 implementation requires an external level shifter, which is usually limited to a 1M baud rate. The FTDI VCP device driver is compatible with standard Win32 COM APIs.