Andy,
You are absolutely right. Hence the phrase "virtual 550". The reference to direct serial is the "technique", hooking the interrupt, setting up and servicing the "virtual" '550.

Now if another program tries to attach to the port, you will find Windows will try to stop this from occurring (for both Win and DOS) executables. This is because, unlike other forms of resource virtualization (like memory) you are "really programming" the '55, you are just falling through the virtualization engine to do this.

regards,
p