I am looking for a device that can provide a sort of parrellel bandwidth. For example my isp provides 5mbps download speed, can a switch allow a peak simultaneous download of 5mbps for each port or is there another device that can do that?
How a switch works is it reads the destination address of each packet that comes in and sends it to that port only, so it only uses bandwidth on the port(s) that need it.
There's no way to get a switch/hub/router/etc., to give more bandwidth than your ISP will give you. So, if ISP gives you 5mbps, you have the option of using it all on 1 PC or sharing the 5mbps between the PCs but without your ISP giving you more bandwidth there's no way to get more than 5mbps out of it. (can't stick 10lbs of ...stuff... in a 5lb bag).
Between your PC's it runs at full (usually 100mbps or 1000mbps) speed, and the switch makes it so you can transfer between PC's 1&2 at the full 100mbps speed at the same time as transferring between 3&4 at 100mbps, and downloading from the internet at 5mbps to PC5.
So, after talking to myself about it (if you muddled your way thru my ramblings you overheard me) a switch does allow 'parallel bandwidth' similar to what you're describing, but since the ISP only has 5mbps of bandwidth, that's all you can get, even though the switch is capable of 100/1000mbps.
Hmm... Just thought of something you may be trying to do. If you get 2 lines from your ISP at 5mbps each, there is a technology called channel bonding (or just bonding) to combine the 2 lines into 1 connection. There were products for dial-up, but I don't know about broadband.
He said that his ISP was an example. If I understand correctly, you want to limit bandwidth by port on a switch, correct? What you want is QoS, available in most high-end (e.g. Cisco, HP) switches. This will allow you to either put a hard cap (e.g. never more than 5Mbps on port 13) or prioritize (e.g. port 13 only gets 5% bandwidth when port 2 is active). This is complicated to configure, though, and I have to ask what you are trying to accomplish? Typically, this setup is used for allowing more bandwidth to power users so their network speed won't be slowed down by the secretary's nail-color spreadsheet she keeps on the server.