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A short class with Sarah and her students. The other ways are under More.
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If I show your marks on the projector and also hand you a printed report card, what is the difference between the two outputs?
The projected one disappears when you switch it off, but the printed one stays with me.
Right. Screen and sound output is soft copy; printed output is hard copy. Now, how does a monitor draw a picture?
With pixels, tiny dots of red, green and blue light.
Yes. A Full HD screen has 1920 pixels across and 1080 down. How many pixels is that?
1920 times 1080, which is 2,073,600 pixels.
Correct, and all of them are redrawn about 60 times every second on a 60 hertz screen.
Some shops still print bills on noisy dot-matrix printers. Why would anyone choose such an old technology?
Because the pins hit the paper, so they can print several carbon copies at once?
Exactly. That is an impact printer. Inkjet and laser printers never strike the paper, so they are non-impact printers.
Which one is better for printing a 200-page project report?
A laser printer. It is fast and has a low cost per page, because the toner is fused onto the paper by heat.
And for colour photographs, an inkjet printer?
Usually, yes. Its fine droplets of ink blend colours well.
Sound is stored as numbers. What turns those numbers back into sound?
A digital-to-analog converter, and then the speaker vibrates the air.
Right. Now think of a student who is blind. Which output devices could help?
Speakers with a screen reader, and a Braille display that raises pins under the fingers.
Good. And which devices work as both input and output?
A touchscreen, a headset with a microphone and a printer that can also scan.
Exactly. Choosing output means thinking about who will use it and how.
Screen and sound output is temporary soft copy; printed output is permanent hard copy.
Screens build pictures from pixels; more pixels across and down give a sharper image.
The picture is redrawn many times a second, for example 60 times on a 60 Hz screen.
Dot-matrix printers strike the paper; inkjet and laser printers do not.
A digital-to-analog converter turns stored numbers back into a signal that drives speakers.
Touchscreens, headsets and multifunction printers do both jobs.
A school printing 2,000 report cards uses a laser printer, which is fast and has a low cost per page, while a shop that must give carbon copies of a bill may still use a dot-matrix printer.
An architect prints a large building plan on a plotter, and a robotics club prints a custom gear on a 3D printer.
Every System.out.println in a Java program sends soft copy output to the screen, which is built from pixels; this program draws a capital A as a 7 × 5 grid in which # is a lit pixel and a full stop is a dark one:
public class PixelGrid {
public static void main(String[] args) {
// 1 = pixel switched on, 0 = pixel switched off
int[][] pixels = {
{0, 1, 1, 1, 0},
{1, 0, 0, 0, 1},
{1, 0, 0, 0, 1},
{1, 1, 1, 1, 1},
{1, 0, 0, 0, 1},
{1, 0, 0, 0, 1},
{1, 0, 0, 0, 1}
};
for (int r = 0; r < pixels.length; r++) {
String line = "";
for (int c = 0; c < pixels[r].length; c++) {
line = line + (pixels[r][c] == 1 ? "#" : ".");
}
System.out.println(line);
}
}
}A screen must hold a full picture in memory every time it is redrawn; this program works out the pixels and bytes in one Full HD picture at 24-bit colour (2,073,600 pixels and 6,220,800 bytes, about 5.93 MB):
public class FrameSize {
public static void main(String[] args) {
int width = 1920, height = 1080; // Full HD resolution
int bytesPerPixel = 3; // 24-bit colour: 8 bits each for red, green and blue
long pixels = (long) width * height;
long bytes = pixels * bytesPerPixel;
double mb = bytes / (1024.0 * 1024.0);
System.out.println("Pixels on the screen: " + pixels);
System.out.println("Bytes for one full screen: " + bytes);
System.out.println("That is about " + Math.round(mb * 100) / 100.0 + " MB");
}
}Soft on the screen, hard on the sheet, pins hit the ribbon, lasers are neat.
A cricket score travels from the computer three ways: it glows on the stadium screen (soft copy), booms from the speakers (sound) and is printed on tomorrow's scorecard (hard copy).
Dots Strike, Ink Sprays, Laser Fuses: dot-matrix strikes, inkjet sprays and laser fuses toner.
R.G.B.: Red, Green, Blue, the three colours every pixel mixes.
Term
Is a document shown on a projector soft copy or hard copy?
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Term
Why can a dot-matrix printer make carbon copies when a laser printer cannot?
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How many pixels does a 1920 × 1080 screen have?
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What does a 60 Hz refresh rate mean?
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What does a DAC do in sound output?
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Hardware that converts the results of processing into a form people or other machines can use.
Temporary output shown on a screen or played as sound.
Permanent physical output, usually printed on paper.
The smallest dot of a screen image; each pixel mixes red, green and blue light.
The number of pixels across and down a screen or image, such as 1920 × 1080.
The number of times every second the screen picture is redrawn, measured in hertz (Hz).
A printer that prints by striking an inked ribbon against the paper, such as a dot-matrix printer.
A circuit that turns stored digital sound into a smooth electrical signal for speakers.
Output devices take the results of processing, held inside the computer as binary data, and present them in a form people can see, hear or touch: on a screen, on paper, as sound or as movement.
Output is the last stage of the input-process-output cycle. This lesson separates soft copy output (screens, sound) from hard copy output (printouts), explains how monitors build pictures from pixels and what resolution and refresh rate mean, compares impact printers (dot-matrix) with non-impact printers (inkjet and laser), and describes plotters, 3D printers, projectors, speakers, Braille devices and devices that work as both input and output.
An output device is hardware that converts the binary results of processing into a form that people, or other machines, can use. Without output, a computer could calculate the answer to any problem but would have no way of telling anyone.
A monitor shows text and pictures as a grid of tiny dots called pixels. Each pixel has red, green and blue parts whose brightness is mixed to make every colour.
A projector throws an enlarged picture onto a wall or screen, so a whole class or meeting can see it.
An impact printer prints by physically striking the paper, while a non-impact printer prints without striking it. Printer speed is measured in pages per minute (ppm) and print quality in dots per inch (dpi).
Two special printers:
Speakers and headphones turn digital sound back into sound waves. A digital-to-analog converter (DAC) changes the stored numbers into a smooth electrical signal, which makes the speaker's cone vibrate and push the air.
Some devices handle both input and output. A touchscreen shows the picture and senses touch, a headset has speakers and a microphone, and a multifunction printer prints (output) as well as scans (input).