Over the years I have made a hobby of collecting real copies of the hardware that we emulate inside of our virtual machines. And this is one of my favorites – the quad-port Intel 21140 network adapter:
One of the interesting problems that we hit while working on Virtual Server was:
How do you support up to four Ethernet adapters and four SCSI adapters at the same time?
You see, you can only have so many PCI devices in a computer (even a virtual one). The answer ended up being quite simple: multi-function devices. So when you are using Virtual PC / Virtual Server / Hyper-V and you configure 2 or more network adapters (legacy network adapters for Hyper-V) what you are actually configuring is a single network adapter with multiple ports on it – each with its own MAC address.
Of course; this makes no difference to the user. It still looks and feels like you have multiple separate network adapters. The only noticeable benefit is that it actually works!