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Ross Herbert

On Wed, 20 May 2009 21:22:01 -0700, wrote:

:
:Actually, not at all. Swapping green and orange swap whole pairs, not
:swap wires within each pair.
:
:They get tighter as you move up, away from the blue/white pair. On a
:25 pair CAT 5 arrangement, the last pair, voilet/grey, is twisted so
:tight it's hard to unravel. At the frequency most establishments run
:at, the impedance difference between the O/W and G/W doesn't add up to
:a hill of beans.
:
:I'm not into the arguments used in favour of twisted pair cable. The

nly reason they are getting away with twisted pair at 100 Mhz is
:through liberal use of bs. For one, the signals are digital and even a
:barely legible digital signal can be picked out of background noise
:with a Schmidt trigger. Try connecting a high-frequency analog signal
:through twisted pair and see how far you get.
:
:Another matter is the claimed throughput as opposed to the actual
:throughput. Most telecom signals are regulated to 30 Mhz to prevent
:broadcasting of signals to adjacent equipment. That means the 100 MHZ
:claimed for CAT 5 regular is never used at that frequency. It could
:be, theoretically, but it never is because signals are multiplexed to
:get that throughput while running at a much slower frequency. A good
:example of that is the DSL signals sent down a normal telephone
:twisted pair which is rated at about 10 Mhz on a good day. DSL is
:accomplished with quadrature modulation, which piggy-backs signals on
:top of each other.
:
:Talking about 1 Ghz twisted pair is a serious joke. They get that by
:using all 4 pairs on the cable, plus multiplexing. There's simply no
:way that twisted pair will ever catch up with coaxial cable and you
:simply cannot use a twisted pair line at 1 Ghz. The big push on
:twisted pair is due to how much more easily it can be installed than
:coax. It makes far more sense to install twisted pair in a hub
:arrangement than it does coax. It's far more economical.
:
:Now we're seeing a push towards SATA over PATA. Although a hard drive
:is a serial device, and a PATA signal has to be serialized to write to
:the hard drive, I don't see what's being accomplished by converting to
:SATA. Again, the only real advantage is a skinnier cable and the
:ability to hot-plug the units.
:
:It just makes no sense to push data transfer one bit at a time when
:you can do it 32 or 64 bits at a time in parallel. Then again, I wont
:be making the kind of money Intel will by cornering the market with
:unnecessary SATA technology. We should remember what happened to IBM
:and OS2 when they tried to foist a technology on a public that did not
:want it.
:

AIUI, the lan cabling base rates are UTP (or STP) ethernet 10BaseT, 100BaseT or
1000BaseT. This means that the "data transfer rate" is either 10Mb/s, 100mb/s or
1000Mb/s.

There is no MHz transmission bandwidth involvement at all.