What difference does it make whether the computer uses USB Ethernet Adapter, or a network card?

Question

Just what the title states.

I'd like to know what difference it makes to the modem/switch, speed, power consumption whether the computer is connected by a USB Ethernet Adapter instead of a physical network card installed into a PCI slot.

As a corollary, it would be nice to know which you would recommend to a nouveau at networking.

Solution 1

Computer technician weighing in here...

Just as the other posters have said, your best bet is an internal network card. This is for the following reasons:

1. USB IO is controlled by the CPU and USB network cards cannot use DMA--this means CPU usage grows with network traffic;
2. The USB bus is shared, which means one thirsty peripheral can (in a severe case) impact the performance of other peripherals such as hard drives and may affect the latency of HID peripherals such as mice and keyboards;
3. There are very few ethernet chipsets and they all have solid, tested drivers which are used directly to support PCI cards--when the USB interface is added, an additional driver is necessary to "glue" the chipset to the USB bus;
   • Drivers are easy to mess up, particularly when small companies are involved.

In theory, systemic power usage would be greater for a USB adapter because of the additional CPU overhead that cannot be off-loaded to a dedicated chip. This may not be the case for high-throughput cases, though (read: I am really just making an educated guess).

Solution 2

I would always recommend a dedicated card/adapter over anything USB whenever it is practical.

USB is good for convenience, but should never be used for critical components where it can be helped.

I do not have any figures regarding power or speed.

That being said, I am sure it "can" support full 100Meg networking speed - I am not entirely sure and would doubt about gigabit speed.

If you go back a few years to when many ISPs gave USB networking, they were always causing problems. The most common is that when the CPU is being used intensively (e.g. above 80%), it wasn't uncommon to see packet loss and other errors.

Solution 3

A USB Ethernet adapter IS a network "card". They are the same for all intents and purposes. I am not sure which takes more power, a PCI slot or USB, but it is negligible considering the DC voltages that used internally.

I still prefer an internal network card, but only because I don't like things handing off my computer, if at all possible. And such things can break off.

Comments

[Moab]

Some report problems when gaming with usb ethernet, a card on the motherboard will outperform a usb adapter under these situations.

[hicklypups]

There are gigabit USB adapters.

[Linker3000]

Just to clarify - should #1 be: USB IO is controlled by the CPU and USB network cards cannot use DMA

[Alex Hirzel]

You're right! I've changed my post.

[Cajunluke]

@KCoutreau Power usage has nothing to do with the internal DC voltages. For instance, the iPad will pull more power from a USB port than almost any other device, even though the port never goes above 5V. (To get increased power, the device increases the amperage.)

[CarlF]

+1 on the above, but note that many PCs have two or more USB buses, so not all peripherals share the same bus.

[Alex Hirzel]

They share the same CPU though. Multiple cores nonwithstanding...

[William Hilsum]

What I was trying to say... but you did it much better!

[sawdust]

What makes you think USB cannot use DMA? USB host controllers can certainly use DMA. There's nothing to stop the Ethernet MAC from using DMA to its local memory.