USB vs PCI wireless network adapters.

[Morpheus]

I have a friend setting up a wireless network, and was researching USB vs PCI.  Here are my finding for my research so far.

A USB adapter is not necessarily the best possible solution.
Here is why:
Your router is the 802.11G standard which means it has a theoretical bandwith of 54 Mb/s (Mega bits per second, 8 megabits make up a megabyte) actual bandwith is usually around 20 Mb/s the connection strength impacts this a lot (a card with a better antena will work better)

There are 2 possible types of USB ports on a computer, 1.1 and 2.0
Bandwidth on a 1.1 port is approxiamately 12 Mb/s
Bandwidth on a 2.0 port is approxiamately 480 Mb/s
If you have multiple USB devices plugged in, the bandwidth gets split (how it gets split can be complex)

You internet connection is probably in the 4-7 Mb/s range

Bandwidth for the PCI bus (which is where the cards get plugged into) is 133Mb/s (shared among all devices)

So if you are surfing the internet at 7Mb/s, and your router is then sending that to the USB adapter at 54 Mb/s, and the port is a USB 2.0 port (480Mb/s) with nothing else plugged into it that is using much bandwith, you are sufing as fast as your connection allows.

If you are on a 1.1 port (12Mb/s) you should still be ok as long as no other USB devices are plugged into the same controller (controllers are the chips on the motherboard, and usually have 2+ ports on the outside of the computer).  If you have other devices plugged in the 12Mb/s is split up, and therefore you might be slowed down by the USB port.

Now things change if you are copying files from one computer on your network to another computer on your network.  If one computer is connected to the router by an ethernet cable, the bandwidth is 100Mb/s.  The wireless connection can only use 54Mb/s therefore you are limited by the wireless bandwidth, and if the USB adapter is plugged into a 1.1 port then it is restricted even further to 12Mb/s.  This is a significant loss in speed.

Bear in mind that all the throughput is the maximum THEORETICAL bandwith...nothing ever gets all available bandwidth.

So the short story is that a USB device, in certain circumstances (specifically transfering files between 2 computers on a network, and not surfing the web) will be slower than a PCI adapter (PC Card for a laptop, or PCI card for a desktop).

Are there any errors or wrong conclusions?

Thanks for feedback!

[JollyRoger]

For the most part I believe your right. But one factor I have found to be a major draw back other then speed is, compatibility. Not on the computer end but on the router end. I have found that some routers and USB Wirelss adapters don't talk.

Another factor is range, USB Adaptors have limited reception. So you signal/noise ratio might be hight, you may loose conection.

My personal opinion is to go with a PCI adaptor.

[ZWarrior]

You have a good set of details there and you are most right.  USB is only the answer when you can't add a card.

For the record, actual max bandwidth utilization is figured to be around 1/3 theoritical max as a rule of thumb.  So a 10Mb/s connection will only allow you about 3Mb/s, and a 100Mb/s connection in hte neighborhood of 30Mb/s.  This is due to overhead, etc.