what is the bandwidth of copper?

Answer 1

*Using multiple pairs of copper enables service providers to offer more than enough bandwidth, for instance, to run Ethernet at 10 Mb/s at a distance of more than 12 kilofeet from the central office.
*[1) A range within a band of frequencies or wavelengths.
(2) The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second(bps) or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).

The bandwidth is particularly important for I/O devices. For example, a fast disk drive can be hampered by a bus with a low bandwidth. This is the main reason that new buses, such as AGP, have been developed for the PC. ]
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Answer 2

Small trace-width microstrip lines (copper) on very thin PCboards are sucessful well past 20 GHz. Some very small geometry coaxial cables are good to 50 GHz (used in some "high-end" test equipment).

What is the absolute upper limit -- I don't know, but the stuff that exists that I know about should give you an idea.

Answer 3

57Kbs I assume, you are talking a standard phone line right? If so, its 57Kbs, but you probably won't achieve that.

As far as CAT5E, you can get up 100Mbs