Peripheral devices are computer devices, such as a CD-ROM drive or printer. Peripheral devices can be external, such as a mouse, keyboard, printer, monitor, and scanner. Peripheral devices can be internal, such as a CD-ROM drive or internal modem.
Computer keyboard is the set of typewriter-like keys that enables you to enter data into a computer. Computer keyboards are similar to electric-typewriter keyboards but contain additional keys. The keys on computer keyboards are often classified as follows:
alphanumeric keys — letters and numbers
punctuation keys — comma, period, semicolon, and so on.
special keys — function keys, control keys, arrow keys, Caps Lock key, and so on.
The standard layout of letters, numbers, and punctuation is called QWERTY keyboard because the first six keys on the top row of letters spell QWERTY. The QWERTY keyboard was designed in the 1800s for mechanical typewriters.
There is no standard computer keyboard, although many manufacturers imitate the keyboards of PCs. There are actually three different PC keyboards: the original PC keyboard, with 84 keys; the AT keyboard, also
With 84 keys; and the enhanced keyboard, with 101 keys. The three differ somewhat in the placement of function keys, the Control key, the Return key, and the Shift keys.
In addition to these keys, IBM keyboards contain the following keys: Page Up, Page Down, Home, End, Insert, Pause, Num Lock, Scroll Lock, Break, Caps Lock, Print Screen. What is a Hard Disk Drive (HDD)?
Hard disk drive is the mechanism that reads and writes data on a hard disk. Hard disk drive has many inflexible platters (discs) coated with magnetic material. Read/write heads can record computer data on these discs. Atypical hard disk rotates at 3,600 revolutions per minute, and the read/ write heads ride over the surface of the disk on a cushion of air 25 micron deep. Hard disk drives (HDDs) for PCs generally have seek times of about 12 milliseconds or less. Hard disk drives are sometimes called Winchester drives. Winchester is the name of one of the first popular hard disk drive technologies developed by IBM in
What is a Monitor?
Monitor is another term for display screen. First monitors were black- and- white with cathode ray tube. Nowadays most monitors are colour monitors. Besides, colour LCD monitors are becoming more and more popular. Monitors have different screen sizes. Like televisions, screen sizes are measured in inches from one corner of the screen to the opposite corner diagonally. A typical size for small monitors is 14 inches. Monitors that are 16 or more inches diagonally are often called full-page monitors.
cathode ray tube — электронно-лучевая трубка Questions:
How are the keys on computer keyboards classified?
How is the standard layout of keys on a keyboard called?
How many keys has enhanced keyboard?
How are hard disk drives sometimes called?
What is hard disk drive?
How are monitor screen sizes measured?
What is a Mouse?
A mouse is a device to move the cursor or pointer on a display screen. As you move the mouse, the pointer on the display screen moves in the same direction. You can roll a mouse on a hard, flat surface. It looks a bit like a real mouse because the connecting wire looks like a mouse tail. Mice usually have two buttons and sometimes as many. as three, which have different functions depending on what program is running. Some newer mice also have a scroll wheel for scrolling through long documents.
The mouse was invented by Douglas Engelbart of Stanford Research Center in 1963. The mouse frees the user from using the keyboard. Mouse is important because you can simply point to objects on the screen and click a mouse button.
Mice can be:
1. Mechanical with a rubber or metal ball that can roll in all directions. Mechanical sensors in the mouse detect the direction the ball is rolling and move the screen pointer.
2. Optomechanical with optical sensors to detect motion of the ball.
3. Optical with a laser to detect the mouse's movement. Optical mice have no mechanical moving parts but they are more expensive.
4. Cordless infrared mice send infrared or radio waves to communicate with the computer. What is a Microprocessor?
Microprocessor is a silicon chip that contains a CPU. The terms microprocessor and CPU are used interchangeably. At the heart of all personal computers sits a microprocessor.
Microprocessors have basic characteristics:
Computational bandwidth: The number of bits processed in a single instruction.
Speed: Given in megahertz (MHz), the speed determines how many instructions per second the processor can execute.