Modern laptops just have a few USB ports and to extend thoose you are supposed to use a USB hub. My issue is that I need to connect 4 highspeed USB 2.0 cameras to my laptop and while still keeping two USB port free (mouse + usb-stick). On a normal USB 3.0/2.0 hub all connected USB 2.0 devices share the same ~40mb/s bandwidth limit, but each camera needs the full 40mb/s on it's own. So is there any way to get more full speed USB 2.0 ports on a modern laptop?
Since you have listed the Thunderbolt tag, it is worth looking into a Thunderbolt dock with USB ports. In the case of Thunderbolt 1 or 2, I believe there are not USB ports routed with the connector, so any external USB ports would be on an external controller. In the case of Thunderbolt 3, since those ports are often paired with USB-C, the dock may be cheating for the USB and just be a USB multiplexer.
If you think a Thunderbolt dock is the way to go, I would suggest getting one with a good return policy and measuring it to make sure it fits your needs.
However, there is always a more exciting option.
Depending on the age of the laptop and what ports you have available, you can consider an M2. to USB 3.0 adapter or a Mini-PCIe to USB 3.0 adapter. Both of these would vastly compromise the portability of any laptop connected to them, but would be a simple and cheap answer to "how do I get more USB ports"
Mini-PCIe does not provide any USB 3 ports, so that adapter almost certainly has its own controller. In the case of M.2, it is almost certainly just routing out the USB ports in the connector, which (hopefully) go straight to the CPU, so should be full-bandwidth.
I cannot post any more links, so some naked suggestions follow
The Mini-PCIe does provide one USB 2.0 port which (hopefully) is connected straight to the CPU. This is cheaper than the USB 3.0 option, and is less likely to be a driver disaster.
Another option in a similar vein is to get a PCIe USB 2.0 card and a M.2 or Mini-PCIe to Desktop-Form-Factor PCIe. The laptop is now totally non-portable, but has a great many USB ports.
Finally, I don't know your usecase, but it may work to get two cheap and junky laptops and connect two cameras to each.
It is very likely that your laptop has only ONE USB host controller. The aggregate bandwidth is determined by controller architecture. So, one controller - 40MBps.
To accommodate 4 USB 2.0 HS cameras, you would need FOUR controllers in your system.
If it is a less-modern laptop (that has one separate EHCI and one xHCI USB 3.0), then connecting one camera to USB 3.0 port, and another to a USB 2.0 will give you the bandwidth for two cameras, but you need to check how your exposed ports are routed, to which controller. If there is only one xHCI, then no luck. And I doubt that your laptop has more than one M.2 slot with direct PCI.
ADDITION: Here are my quick results.
On old and not so old Intel machines, EHCI (USB 2.0) controllers (at least on relatively new C20x chipset, 2011, and on all older ICHx chipsets) split the available ~42 MBps bandwidth between all root ports.
Renesas USB 3.0 xHCI add-on PCIe card controller also splits the 42 MBps between ports;
ASMedia USB 3.1 Gen.2 controller on 4X PCIe slot also splits the bandwidth;
Only newest Intel xHCI USB controllers, Braswell family and newer (2015) do provide full USB 2.0 bandwidth on individual ports (verified on three ports, I don't have more).
Any internal or external USB 3.0 hub will split the USB2 bandwidth between ports.
Therefore, I stand corrected regarding the latest Intel eXtensible Host Controllers - they do provide full USB 2.0 (~42 MBps) on each port.
Consider using a USB 3.0 hub.
Alternatively, there are hubs designed to be USB 3.0 to multiple 2.0s and (some of) they should work, too.
A hub is basically a chip connected with ports and a plug. The chip runs for the hub and manages data between devices and host. So if you use a host with USB 3.0, you'd be able to divide its speed (bandwidth) into multiple USB 2.0 ports, as long as the hub supports.
Beware with 7-port hubs. I dismantled a few and found there were 2 chips connected together, so 4 ports will be slower than the other 3.