The older Raspberry Pi B models come standard with 4 USB ports. Even so, it only has one root USB port where all traffic is funnelled too. It operates at a maximum speed of 480mbps (USB 2.0).
Table of contents
Raspberry Pi USB port speed
Global USB specification defines three device speeds –- low-speed (USB 1.1 – 1.5mbps), full-speed (USB 1.1 – 12mbps), and high-speed (USB 2.0). The Raspberry Pi defaults to high-speed.
It is said that there are generally no issues with connecting multiple high-speed USB devices at the same time, but my own experience tells me that there are soft limitations on the number of simultaneously active low- and full-speed devices.
Changing the port speed
In some cases one might need to change the USB port speed for older hardware to full-speed (i.e. USB 1.1) use:
sudo nano /boot/cmdline.txt
and appending the following:
to the very end of the line.
Another important thing about the Raspberry Pi USB ports is that they will only supply 100 mA per port.
This means that “low-power” devices like USB drives, keyboards and mice will work sufficiently, but if you start to get abnormal behaviour, like devices stopping without a reason, brownouts and/or unexpected resets, you should probably get an external USB hub with its own power supply.
Devices such as Wi-Fi adapters, USB hard drives and USB pen drives are known to consume much more than 100mA. It is also noteworthy that in order to supply even low-power devices with sufficient current, the Pi should also be supplied with a proper power supply.
The people at the Raspberry foundation recommends 5V with at least 1.2A (1200mA).
Effect of overclocking
I have heard somewhere that when the Raspberry Pi is overclocked, it will supply less Amperage.
The Raspberry Pi
To get started with the Raspberry Pi you will need the following:
We have tested most of these products ourselves. Other selection criteria include affordability, quality, availability and average user rating and popularity by other buyers.
Links will open in a new window. (Dead or old links can be reported in the comments section below.)