There are a variety of ways in which computers communicate. Firstly, they can be said to communicate with the user since you put information in and get something out. If you use a database it can organise your data and then tell you how that data would look organised in a particular way. However, this section is concerned with connecting computers together and getting them to talk to each other.
The simplest way of connecting computers is simply to stick a wire between
the two. But that does nothing to translate the information nor does it control
the conversation. In a human voice conversation you can see the other participant(s).
If you are talking they are not; they are listening. But they may interrupt
and two people may talk at once. In any event there is still some control or
signal as to when the other is talking.
What happens in the computer world is that we add several wires. Ususally there is one to send and one to receive (talk and listen). This allows talking at once (full duplex) rather than just one at a time (half duplex). In addition, there are wires for signalling or control. Software controls what is happening at any time. Now, although operating systems allow you to set the speed of any ports the communications software often overrides this and sets the speed itself. Indeed, there is usually an option somwhere to specify a speed (although this may be a maximum).
In order that one machine can talk to another the wires must have the same meaning for each end. To this end there are defined standards one being RS232 (a variant being RS423) which coincidentally is used for serial devices like serial printers.
In 1979 Intel, DEC and others announced a high speed local area network called
Ethernet using coaxial cable, broad transmission and variable delays in the
event of asion. It was quickly adopted by many companies and Intel later built
a single chip controller for it. It is now the standard for LANs (Local Area
Networks).
Connecting computers directly by cables is not the only way to connect computers together. True, it gives a permanent link, but this is not always needed. We can use a normal telephone line instead. This means that when not connected our machine is protected from invasion. There are a variety of phone technologies each of which give different communication speeds. Follow the link for more information.
In 1967 the information service known as CompuServe was founded. Hayes Microcomputer Products announced the Micromodem in 1979 to access it with features such as auto-dial, auto-answer it transmitted at 110 to 300baud (bits per second or bps) and retailed for $399. Communications speeds have increased dramatically since then reaching the theoretical maximum for copper telephone wires of 56kbps. In practice, this top speed is never reached due to line noise and other factors. Modems either fit inside the computer or attach to a serial port so are external. External modems have small lights (LEDs) so that you can see what they are up to. There are software solutions to implement this for internal modems since being inside the machine you can't see what them at all! The software gives an indication your screen. A modem simply turns the electrical signals your computer produces into audio tones for transmission down the phone line. Incoming tones are converted back by the modem.
The modem negotiates with the remote computer to establish a connection speed.
Initially (if you are able to look at the speeds) you will see the rate at which
the modem is transferring data to the communications port in your computer for
processing. This is called the modem to DTE speed. It is not the speed at which
the modem pushes data down the phoneline. That's something different. The modem
to modem or DCE speed is the speed along the phone wires. Speeds are measured
in bits per second. a 56k modem is capable of sending data at 56,000bits per
second (56kbps). A byte is 8 bits. A 100k file will therefore take 100 x 1024
x 8 bits (819,200 bits) 819.2 seconds at 1kbps or 128bytes a second (0.128K/s).
A fast processor will process incoming data quickly thereby leaving the "hallway"
(ie buffers) clear or ready for new data without holding up the datastream.
Faster modems monitor the line to achieve the best speed at any time so speeds
can vary throughout a session.
However, data passes through a number of hops or routers when travelling any distance and when several computers are connected in a network. The hops should form the fastest path at a particular moment in time. The larger the number of hops the more likely the data is to be slowed down therefore slowing your connection. Again the more traffic there is on a network the slower your connection since the equipment between you and the remote computer has do deal with more data and requests for transfers. If the information you want to retrieve is popular then the remote computer has more people to deal with and as each is given fairly equal attention upto a maximum number of connections the more people there are trying the smaller the share of time you get and therefore less attention. Sometimes you won't be able to access the remote computer because it can only deal with so many people and that limit has been reached.
Data is often compressed for transfer. This means large amounts can be transferred in a small amount of time. Text is easy to compress but video and graphics are less easy. There are different ways of compressing data and some do not spread the "load" evenly throughout the file. Consequently speeds can vary throughout the transfer.
Modern machines use drivers which are special bits of software to enable the
modem to talk to the computer and carry out its operations. It's worth making
sure you have up to date ones as they can be more optimal and problems with
older drivers are fixed.
Interference and static can result in data loss on the phone line resulting in slower connections and possibly dropped connections. It's often worth looking at what other equipment is situated near the phone cables and any extension leads and seeing if anything can be relocated. Quality can also be affected by the quality of the line. The exchange can check the line quality and can also change the gain or frequency of the data transfer (the suggested gain is 3) which potentially can make the connection better.
In any discussion of computer communications the internet has to be mentioned. Many people think of this as a recent innovation but in fact it dates back to the late 1960s when a group of acamedicians put together a private network.
The internet (or net) actually consists of several bits. The most common (and that which everyone thinks of these days as the internet) is the world wide web. Email, chat (IRC), newsgroups and FTP are also internet uses. Some of the older ones are archie and gopher. The World Wide Web (www) was invented by a British guy called Tim Berners-Lee
Communications Modems Domain Names More about URLs MIME Email Interactivity Search Security
Contents Introduction Input Numbers CPU and Memory Operating systems Disks Links Glossary Contact Bibliography