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Q: WHAT is actually sent from 1 computer to another? ( Answered,   10 Comments )
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 Subject: WHAT is actually sent from 1 computer to another? Category: Science > Technology Asked by: wumply-ga List Price: \$2.00 Posted: 29 Mar 2006 19:25 PST Expires: 28 Apr 2006 20:25 PDT Question ID: 713418
 Can I be directed to sites that hopefully will precisely answer my question? Here it is: As I currently understand things... A "1" represents a voltage; it pushes electrons over computer wires and eventually over a communications network. A "0" represents a "no voltage"... nothing is happening--no electronics moving along the wires/networks. So is the transmission of information from my computer to say a host computer a changing series of electron flow periods interspersed with a periods of "no electron" flow periods depending on the sequence of voltages and 'no voltages' presented? And at the receiving computer's end, the circuitry there distinguishes between a voltage and a 'no voltage' and says: "Oh, I've got a "1" and a "0"? So, assuming the above is correct, I can conclude/summarize that what actually goes on in transmission of information is that electrons move along the communications network but that also there are periods when electrons do not move over the wires and the transistors and chips or circuits (whatever) can distinguish between electron flow and "no electron" flow? And thus our ones and zeros get from A to B? And in fiber optic lines you simply have a light impulse vs "no impulse" replacing a electron flow vs "no electron flow"? Or HOW DOES it work? And if any readers of this question are tempted to comment I hope they will!
 Subject: Re: WHAT is actually sent from 1 computer to another? Answered By: hedgie-ga on 17 Apr 2006 23:58 PDT
 Your grasp is correct, and comments are good, but you did not expire the question, so I will try to find what you asked for, namely few links which explain the process. But first, comment about electrons: those are always moving, quite fast, depending on temperature (of the wire). When voltage is applied (to the two ends of the wire) the 'drift velocity' is added to the thermal motion. http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/DC-Current/Current.html That's Ohm's law. http://www.semiconphysics.com/carrier-drift.htm Now few links on networks: There are 7 layers http://en.wikipedia.org/wiki/OSI_model You are interested in the lowest, physical layer http://en.wikipedia.org/wiki/Physical_layer which can be implemented by wire, fiber optics, emg (wireless radio) link etc Here is 'a practical guide' how to do 'the cabling' http://www.ciscopress.com/articles/article.asp?p=169686&rl=1 and here (good visual) presentation of those marching bits http://compnetworking.about.com/od/basicnetworkingconcepts/l/blbasics_osi1.htm You will get more references when you enter into search engine SEARCH TERMS: OSI, Physical Layer combined with : fiber, electric, voltage, etc Rating appreciated. Hedgie
 Subject: Re: WHAT is actually sent from 1 computer to another? From: probonopublico-ga on 29 Mar 2006 20:55 PST
 Of course, you don't need 'wires' ... There's no wire connecting my computer with yours ... At least, none that I can see even though there's a MASS of wires behind my desk. I'm beginning to wonder ... What are all those wires for?
 Subject: Re: WHAT is actually sent from 1 computer to another? From: kottekoe-ga on 29 Mar 2006 21:57 PST
 Wumbly, Yes, you grasp the concept correctly. In reality things are a little more complicated and variable, but the scheme you describe is one way that works. The "1" and "0" (which we could just as well, and often do, call "true" and "false", or "high" and "low") can be represented in many ways. In some systems a "1" is a positive voltage, while a "0" is a negative voltage. In other systems the "1" might be a voltage that oscillates at a particular frequency, or a voltage that goes up during a particular interval of time. As you point out, a "1" can also be a flash of light. On a disk drive, a "1" could be a tiny magnet with its north pole pointed "up". On a DRAM a "1" is a bunch of electrons on a tiny capacitor plate. In a radio link or DSL connection, you often use many different codes instead of just two. For example, each transmitted symbol might be one out of 256 symbols uniquely represented by the amplitude and phase angle of a rapidly oscillating signal. The beauty of it all is that information of any kind can be represented arbitrarily well with a finite number of these "bits" (binary digits) of information.
 Subject: Re: WHAT is actually sent from 1 computer to another? From: sorwin-ga on 30 Mar 2006 14:44 PST
 It is NOT helpful to regard logical "1" or "0" as represented by voltage levels. Such representation may or may not be correct, depending upon circumstances. "1" and "0" usually represent binary numbers in Boolean algebra, for example: 000 = 0 001 = 1 010 = 2 011 = 3 100 = 4 101 = 5 110 = 6 111 = 7 and so-on. The above shows binary numbers in 3-bit bytes. Most PC's use 32-bit bytes, so the maximum number conveyed by a 32-bit byte is 2 to the power 32 minus 1 = 4294967295 What the numbers represent could be anything and depends upon the application and its context.
 Subject: Re: WHAT is actually sent from 1 computer to another? From: kottekoe-ga on 30 Mar 2006 18:21 PST
 Sorwin, On the contrary, if you are trying to understand how a computer works, like Wumbly, it is quite useful to think of "1" and "0" as representing voltage levels. In many cases that is how the bits are encoded. On a CMOS chip, where most of the computing happens, that is exactly how it works. The MOS transistor is controlled by a voltage and used to produce a voltage to drive the next level of logic. P.S. A byte is always 8 bits, by definition. A "word" can be any length.
 Subject: Re: WHAT is actually sent from 1 computer to another? From: wumply-ga on 01 Apr 2006 18:14 PST
 So kottekoe-ga, would you confirm or correct THIS...since I want to be very sure. Instead of using a positive voltage for a "1" and a "no voltage" for a "0" we used a +2 voltage for a "1" and a -2 for a "0", it's truly analogous...it's the same electron flow/no electron flow? Yes, it is pretty darned amazing!
 Subject: Re: WHAT is actually sent from 1 computer to another? From: kottekoe-ga on 01 Apr 2006 22:32 PST
 Wumply, Yes, you could use +2 V and -2 V as your logic levels if there was a good reason to do so. Since no voltage are ever exact, you might define +2 V and -2 V as the nominal values, but allow anything above +1 V to be considered a "1" and anything below -1 V to be considered a "0". In general, you can use any encoding scheme that is convenient, but there are industry standards to allow circuits to interoperate. In voltage controlled logic circuits, usually a voltage lower than a certain value Vil is "Low" and a voltage above a certain value Vih is "High". "0" is usually, though not always, represented by "Low", while "1" is represented by "High". For example, you can find the standard voltages for various integrated circuit families at this URL: http://www.interfacebus.com/voltage_threshold.html Some logic families use a negative voltage for Vil and a positive one for Vih, but it is more common for both voltages to be positive. And yes, in these circuits the electron flow changes with the voltages. If the voltage changes from positive to negative, the flow of electrons will change from one direction to the opposite direction.
 Subject: Re: WHAT is actually sent from 1 computer to another? From: baruch60610-ga on 03 Apr 2006 05:19 PDT
 The method of transmission is electrical. The precise details are a bit confusing. For example, when you have a positive (or non-zero) voltage, that means that the flow of electrons is *less* than when you have a zero voltage. And the electrons don't move much. This will drive you nuts if you think about it too much. But your basic understanding is OK - yes, electrical signals are generated on the pins of chips in your computer. These signals are carried along by wires, or sometimes by radio waves (if you're using a wireless system), to your modem or whatever connects you to your ISP. The electrical signals are carried by these wires, or possibly via radio waves to satellites, to other computers. Along the way, the signals may be changed in various ways, depending on where they are. The signals in the wires to the ISP are different from your computer's. Despite this, they retain the important quality of being able to represent two distinct states, which is the essence of the transfer.
 Subject: Re: WHAT is actually sent from 1 computer to another? From: wumply-ga on 03 Apr 2006 14:21 PDT
 baruch60610-ga (or anyone in case baruch doesn't see this post.) Can I ask you WHY the flow of elecrons is less than when you have a "0" voltage? That fact is fascinating!
 Subject: Re: WHAT is actually sent from 1 computer to another? From: isnraju-ga on 04 Apr 2006 19:13 PDT
 The concept of pulse or absence of pulse can make things easier. these pulses can be transmitted wirelessly. further pulse group explained as binary number or 8 based symbol bit is used for each character and received as such. translations of the data from input to machine langauage and back are needed to make sense othis data at the other end. For this reason I conceptualise the data as pulses and this explains the importance of speed as expressed in Giga Hertz and data transfer expressed in bits per second makes easier for me to understand.
 Subject: Re: WHAT is actually sent from 1 computer to another? From: kottekoe-ga on 04 Apr 2006 20:14 PDT
 But the bits may or may not be encoded as pulses. For example a very common encoding scheme is to use positive and negative transitions to encode the bit stream. In this case a long string of zeros (or ones, for that matter) can be a constant voltage that is either high or low.