Every USB <--> RS232 Adapter requires a driver in order to present a COMM port API to the user programs. As a matter of fact under Windows 32 platforms these drivers are a special type called a Bridge Driver that has a USB driver on one side and support for the COMM port API on the other side.

It is possible that some Win2K or WinXP installations may have drivers for certain adapters packaged with the OS install. However it is my experience that this is not the common case. I have had to commonly install the drivers that came on the CD packaged with the adapter cable. Other times the driver is available on-line via the Microsoft Windows Update connection but that takes an active web connection at the time you are trying to install and use your USB-RS232 adapter.

As a matter of fact, just today, I installed a USB to RS485 adapter from RE Smith that uses a FTDI chip inside, onto my WinXP notebook computer. I had to connect the computer to my network so that it could go to Windows Update to get the latest drivers. (BTW . . . . I can highly recommend the use this USB-A4 device from RE-Smith at www.rs485.com. It is an excellent adapter).

There are at least four manufacturers (Prolific, Cypress, FTDI, SiLabs) and quite likely others that make the chips that go into USB <--> serial adapters. The drivers for these things typically come from and are supported by the chip manufacturers. It is not uncommon to buy an adapter and find the driver on its CD to be over 2 years old. If you find this, as I have, it can pay to go the the manufacturer web site and search out the newest driver. In several cases I have had strange or intermittent behavior in the use of USB-Serial adapters with VB6 programs that I have written. In one case I was making use of a whole batch of adapters with Prolific chips that were making WindowsXP BlueScreen. A visit to the Prolific web site revealed a new driver version that made all the previous BlueScreen problems go away.

Michael Karas