НУЖЕН ПЕРЕВОД ТЕКСТА. СРОЧНО
Input devices are the pieces of hardware which allow us to enter
information into the computer. The most common are the keyboard and the mouse.
We can also interact with a computer by using one of these: a lightpen, a
scanner, a trackball, a graphics tablet, a joystick or a voice recognition
The computer keyboard is an electronic device with
keys arranged like earlier typewriter keyboards but with extra keys. They
perform different functions. The computer mouse
is a hand-operated device that lets you control more easily the location of the
pointer on your screen. You can make selections and choices with the mouse
button. A lightpen is a highly
sensitive photo-electric device which uses the CRT ( Cathode Ray Tube ) screen
as the positioning reference. The user can pass the pen over the surface of the
screen to detect, draw or modify images displayed on the screen. A scanner is an input device that scans
(reads) the image as a series of dots and introduces the information into the
computer memory. A trackball is a
stationary device that works like a mouse turned upside down. The ball spins
freely to control the movement of the cursor on the screen. A graphics tablet is an input device
which allows the user to specify a position on the screen by using a stylus.
Tablets are more accurate than other devices. A joystick is an input device with a vertical level used in computer
games to move the cursor around the screen. Voice recognition devices allow computers to listen to your voice
and change what you say into a written message or into orders.
and pictures that we see on the screen are made up of dots, also called picture
elements (pixels). The total number of pixels in which the display is divided
both horizontally and verticailv is known as the resolution. If the number of
pixels is very large, we obtain a high resolution display and therefore a sharp
image. If the number of pixels is small, a low resolution is produced.
resolutions are 640 x 480 or 1,024 x 768 pixels. Pixel density affects the
image: a larger number of pixels gives a much clearer image.
The cathode ray
tube of the monitor is very similar to that of a TV set. Inside the tube there
is an electron beam which scans the screen and turns on or off the pixels that
make up the image. The beam begins in the top left corner, and scans the screen
from left to right in a continuous sequence, similar to the movement of our
eyes when we read, but much faster. This sequence is repeated 50, 70 or 85
times per second, depending on the system. If the rate of this repetition is
low, we can perceive a flickering, unsteady screen, which can cause eye fatigue.
However, a fast-moving 75 Hz 'refresh rate' eliminates this annoying
What we see on
the screen is created and stored in an area of RAM, so that there is a so
memory cell allocated to each pixel. This type of display is called bit-mapped.
On monochrome monitors, bits 0 are visualized as white dots, and bits 1 as