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500 MB Nyheder Direkte fra Internet 2
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500 MB nyheder direkte fra internet CD 2.iso
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screens.txt
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1994-09-21
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12KB
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216 lines
WHAT'S A SCREEN?
The computer's screen is an ordinary TV (the same kind you
watch Bill Cosby on) or resembles a TV. The screen shows what you
typed on the keyboard and also shows the computer's responses.
TELEVISIONS
If your computer can be attached to
an ordinary TV, it's called a TV computer. Here's how to attach a
TV computer to a TV.
Look at your TV's antenna. Wires run
from the antenna to two screws, which are on the back of the TV:
Loosen the two screws, to release
the antenna. When you buy a TV computer, the salesperson also
gives you a switch box. Attach that box to the two screws you
loosened:
The salesperson also gives you an
electrical cord looking like this:
It's called an RCA cord, because RCA invented it. Plug one end of
that cord into your computer, and plug the opposite end into the
switch box.
Attach the antenna's wires to the
screws on the switch box:
The switch box has a switch on it.
If you move the switch toward the antenna, you have a normal TV,
so you can watch Bill Cosby. If you move the switch toward the
computer's RCA cord, your TV's controlled by the computer so that
the computer can write messages on your TV screen.
So by moving the switch, you can
make your TV act either normal or computerized. Your family will
argue about which way to move the switch.
That switch box is the same kind used by video games (such as
Mattel Intellivision, Atari VCS, and Colecovision). When you buy
a TV computer, the salesperson will give you the switch box and
RCA cord, free!
To use the computer, flip the computer's switch to channel 3 or
4, then turn your TV's dial to the same channel.
To get a sharp picture on your TV screen, avoid the channel
used by your local TV station. For example, if you live in Boston
or New York City, NBC hogs channel 4, so avoid channel 4; put
your computer and TV on channel 3 instead.
Although most computers (such as Commodore and Radio Shack) use
channels 3 and 4, some computers (such as Atari) use channels 2
and 3 instead, and some other computers use channels 10 and 33
and 34 instead.
If the image on your TV screen looks fuzzy ___ so that you can
barely read the computer's writing ___ adjust the TV's ``fine
tuning'' knob.
What the TV can do
Besides writing messages on your TV's screen, the computer can
also draw its own pictures on the TV! And if your TV has color,
you'll see the pictures in color!
When you watch Bill Cosby on TV, his face's size depends on the
size of your TV's screen. If your TV's screen is tiny (less than
12 inches), his face looks small; if your TV's screen is 25
inches, his face looks bigger; and if you have a projection TV
with a gigantic 60-inch screen, his face looks gigantic. The
same's true for the messages & pictures sent to the TV by the
computer: the bigger the TV's screen, the more magnified the
computer's messages & pictures.
How much is displayed?
The computer makes the TV's screen show lots of words, numbers,
and formulas. Those words, numbers, and formulas are made of
characters: each character is a letter of the alphabet, a digit,
or any other symbol you can type.
The ideal TV computer would make the TV display 25 lines of
info, with each line of info containing 40 characters, so the
total number of characters you see on the screen simultaneously
is ``25 times 40'', which is 1000.
But most TV computers are less than perfect: they display
slightly fewer than 25 lines of info and slightly fewer than 40
characters per line, so the total number of characters you see on
the TV screen simultaneously is slightly less than 1000.
MONITORS
A computer monitor resembles a TV
but produces a sharper picture and costs more.
Like a TV, a computer monitor uses a
picture tube. The tube in a TV or monitor is called a cathode-ray
tube (CRT).
The monitor can be either
stand-alone or built-in. A stand-alone monitor looks like a TV
but has no antenna and no dial for selecting channels: the only
channel you get is ``computer''. It doesn't need a switch box:
instead, the computer's RCA cord (or similar cord) plugs directly
into a hole in the monitor. Before buying a computer that uses a
stand-alone monitor, ask whether the computer's price includes
the monitor: the monitor might cost extra.
A built-in monitor is a screen
permanently attached to the rest of the computer: the unit
containing the computer's main circuits also contains the
monitor.
Colors
When buying a TV, you ask for either
``color'' or ``black-and-white''. Similarly, when buying a
computer monitor, ask for either color or monochrome. A color
monitor displays all colors of the rainbow; a monochrome monitor
displays just black-and-light.
Four kinds of monochrome monitors
are popular:
A paper-white monitordisplays black
and white.
An amber monitor displays black and
yellow.
A green-screen monitordisplays black
and light green.
A gray-scale monitordisplays many
shades of gray.
A color TV costs more than
black-and-white. Similarly, a color monitor (that displays all
the colors of the rainbow) costs more than a monochrome monitor.
Most monochrome monitors cost about
$100. Most color monitors cost between $200 and $500.
Screen size
The typical color monitor's screen
is 14 inches (measured diagonally). The typical monochrome
monitor's screen is 12 inches, but some monochrome monitors use a
smaller screen (9-inch) to make the monitor be smaller, weigh
less, and be easier to carry.
Fat cables
If the cable running from the
monitor to the computer is fat (so it contains many wires), the
monitor produces a sharp image.
A monochrome monitor with a fat
cable is called a transistor-transistor-logic monitor (TTL
monitor). Its cable contains one wire to transmit the fundamental
picture, plus additional wires for further enhancements.
A color monitor with a fat cable is
called a red-green-blue monitor (RGB monitor). Its cable contains
one wire to transmit red, a second wire to transmit green, a
third wire to transmit blue, plus additional wires for further
enhancements.
For the IBM PC, you can buy three
kinds of RGB monitors: the cheapest are called CGA monitors; the
better ones are called EGA monitors; the best ones are called VGA
color monitors. (I'll reveal more details about those monitors on
pages 68 and 69.)
If your monitor's cable is not fat,
the picture isn't sharp. For example, if your monitor's cable is
just a thin RCA cord, your monitor's called a composite monitor;
its picture is fuzzy, though not as fuzzy as a plain TV.
Most computers (such as the IBM PC)
can make a monitor display 80 characters per line. To fit so many
characters on a line, the characters are made tiny. To display
the tiny characters clearly, the monitor must either have a fat
cable (to produce a sharp picture) or be monochrome; it must not
be a composite color monitor. (If you try to display tiny
characters on a composite color monitor, the characters are hard
to read because the fuzzy colors bleed into each other.)
The typical monitor displays 25
80-character lines, so you see 2000 characters simultaneously.
VIDEO TERMINALS
A video-display terminal (VDT) is a monitor that communicates
with a large computer and has an attached keyboard.
If 200 people are using a maxicomputer simultaneously, only one
of them is sitting at the maxicomputer's main console. The other
199 people typically sit at 199 VDT's, which are in different
rooms or even different cities.
LIQUID CRYSTALS
If your computer is
tiny, it comes with a tiny screen, called a liquid-crystal
display (LCD). That's the kind of screen you see on digital
watches, pocket calculators, pocket computers, notebook
computers, and laptop computers.
Since an LCD screen uses
little electricity, it can run on batteries. A traditional
picture tube cannot run on batteries. If your computer system
runs on batteries, its screen is an LCD.
An LCD screen displays
black characters on a white background. The screen consists of
thousands of tiny crystals. Each crystal is normally white, but
temporarily changes to black when an electrical charge passes
through it.
A traditional picture
tube emits light; that's why you can watch TV even in a dark
room. But an LCD screen does not emit light; you cannot read an
LCD screen in a dark room. You must turn on a light, to see which
of the crystals are white and which are black.
Some LCD screens come
with a light to help you see the screen. If the light is behind
the LCD surface, the screen is said to be backlit. Since the
light consumes electricity, it quickly runs down the battery,
which you must recharge often.
Although the crystals
can change from white to black, they appear black only if you
look at them from the correct angle, and if the light in the room
is positioned correctly. If you move your head or the light, the
black crystals will appear very light gray instead of black, and
you'll have trouble reading the message they're trying to
display. So if you have trouble seeing the message on an LCD
screen, move your head or the light or the screen, until the
message darkens. The fanciest LCD screens use supertwist
crystals, which you can read from any angle; but they're
expensive and consume more electricity.
Laptops use LCD screens
instead of traditional picture tubes, because LCD screens consume
less electricity, weigh less, and are less bulky. Desktops stay
with traditional picture tubes, because the image on the typical
LCD screen has poor contrast and resolution and responds too
slowly to computer commands.
An LCD plate (or LCD
overhead-projection panel) is a special LCD screen that you put
on an overhead projector, which projects the LCD's image onto the
wall of your office or classroom or auditorium, so that the image
becomes several feet across.
The nicest low-cost LCD
plate is the Sharp QA-75. It can display many shades of gray. It
sells for about $1500. It attaches to the IBM PC, and you can buy
a cable to connect it to a Mac.