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The Telegraph
The telegraph was quite a crude device, just an on-or-off switch. All it really did was it sent an electrical blip down the
line. It was like communicating by using the sound of a lamp shorting out. The really brilliant part of the telegraph was
Morse Code, which took that single electrical blip and made it into a language.
Since all you had to work with was a blip, a longer blip, or nothing coming down the line, the trick was to represent
every letter of the alphabet (and some punctuation) with a combination of short and long blips and use the silences as breaks
between words. Skillful telegraph operators could send or receive dozens of words per minute, decoding the sounds by ear and
encoding messages on the fly.
The other important thing about telegraphs was the system that evolved, the telegraph network itself, more than a million
miles of wire by the year 1900, and the social connectedness it created. A variety of specific jobs developed to service the
telegraph industry, from Morse code operators to telegram delivery boys. Older movies often feature references to the (then
very common) culture of the telegraph.
"It's For You Dear...."
The next historical network is still with us today. It's the telephone. You may have seen them around. Perhaps you've even
used one.
It's a little difficult to appreciate the telephone fully, because it is such a major part of our society. It's so useful
it's been an essential device for 100 years and it became a common household item about 50 years ago.
The telephone works great. Because so many people have phones, you can dial a few numbers and connect to anybody. The
phone system basically consists of a lot of wires -- really a lot -- all leading to central switching stations, which connect
my phone to yours when I dial your number. It's all very simple, in principle, although it's a fair bit more complicated in
practice today. With cellular phones and satellite communications, you don't even have to be connected to a land line anymore.
Both the telegraph and telephone systems are analog networks -- they use good old fashioned sound to communicate. Computer
networks, however, are digital networks. Telephone companies, especially AT&T, started changing their networks to digital
systems in order to make automated dialing and switching more possible. We'll talk more about digital and analog in another
lesson.
The first major use of digital networks was time-sharing on mainframes, brought about by advances in monitors and terminals
that allowed people to work online relatively quickly -- well, quicker than with punch cards and teleprinters, anyway. Computers
were so incredibly expensive that it was necessary to try to use them as efficiently as possible. So, while you were entering
your program, somebody else was running theirs. And so it would go around. We are now familiar with the image of many green-screen
terminals connected to a central mainframe. These were the first really important networks.
The Origin of Computer Networks
Computers used to be so scarce (in 1972 there were only about 150,000 in the world) people had to share them. But there
are only 24 hours in a day, so booking them out in hourly blocks (like a meeting room gets booked) might not begin to cover
the demand. Besides, that's a waste. Except for when it's actually doing a calculation, your average computer is bored to
tears, or would be if it could cry. A computer spends most of its time waiting for humans to finish doing something: to finish
typing, to finish reading, to finish printing. Waiting, waiting, waiting.
Time-sharing Computers
Even the building-sized computers we had in the old days spent a lot of time waiting for humans to do something. Eventually,
somebody invented a way to 'time-share' a computer so that several people could use it at the same time from a bunch of different
terminals, like having dozens of keyboards and monitors plugged in all at once. What time-sharingdoes is let a bunch of people
use the computer's computing power one at a time. It does one task and switches to the next. But the computer does that so
quickly that, as far as the human beings are concerned, it's as if you've got the machine's attention full time.
So, the first networks were actually made up of one computer shared by a group of human beings clustered around it. As
the mainframe computer culture peaked in the 1960s and early 1970s, the actual terminals became a bit more powerful, able
to take on some of the duties of the main machine and boost efficiency somewhat. But remote access, like by modem, was still
very rare. Regular telephone modem speeds now are between 100 and 350 times faster than they were in the 1970s.
Computers and Networks
How does a computer change when we plug it into a network?
So far we've considered computers as individuals, like they were the wise old man in the centre of town holding all the
knowledge of the ages or even just as a bunch of fast-acting accurate calculating machines with a big crowd of human fans.
But, just like people, computers can act differently when they're in a group. An individual computer can become much 'smarter'
(because it can access more information or use more software) or dumber (because all it does is queue up the next jobs for
the laser printer). A network of computers is not the same as a roomful of computers, just like a roomful of people is not
the same thing as a roomful of friends.
If you think about it, a computer is actually a network within itself, a group of components that are joined together by certain
agreed-upon standards of communicating (and some wires). The Central Processing Unit (CPU) has a built in set of expectations
of how and what it will send to or receive from each of the other components, such as the video card and monitor, the hard
drive, the disk drive, the keyboard and mouse. Perhaps hundreds of times a second the computer checks the keyboard to see
if you've pressed a key. It also throws a few cycles of its attention at the disk drive, the mouse, or anything else that's
attached to its input ports.
This all comes from the old days of time-sharing, when the 'hard drive storage' of a computer wasn't built in, but was
perhaps a separate roomful of magnetic tape machines on a different floor of the building, and the 'graphic display' was printed
out by a noisy teletype that used to drive people crazy from the sound. All the stuff that we think of as modern desktop computers
are just the minaturized versions of that kind of networked installation that used to be so big it needed a building, and
so rare that people wouldline up to use it.
It is difficult to express all the differences between a computer on its own and a computer as part of a network. In most
ways, when your computer is connected to a network, it is like having more computer available to you. More storage, more software,
more options, sometimes more headaches. With some types of networks, computers can even share processing power to work on
a complex job like high-resolution computer animation as a group. A network adds a lot to the abilities of a single computer.
But, connecting to a network doesn't just represent adding access to more stuff for your personal convenience. There's
something more, something that's hard to define and represents different things to each of the people on a network. Maybe
it's because there are people on the network. Plugging a computer into a network is like giving a remote small town telephones,
a library, and cable TV on the same day. Suddenly you've added access to more information, resources, AND access to all the
people who're connected to that network.
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