
    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.