Computer output devices

Computer output devices

An output device displays information on a screen, creates printed copies or generates sound. A monitor, printer, and speakers are examples of output devices.
i. Monitors and Displays Shows the processed information on a screen. A monitor uses a Picture Tube like a television with the image displayed on the front of the tube, which is called the screen.
ii. Printers produce a hard copy. The information is printed on paper and can be used when the device is off. It is also called a printout. There different types of printers;
a. Dot-matrix printers (impact printer)
Uses metal pins to strike an inked ribbon to make dots on a piece of paper. Lowest print quality of all of the printers. Very low in cost per page to use.
b. Ink jet printers (non-impact printer)
Use drops of magnetic ink to produce dots on a page to produce text or images. The print quality is almost the same as a laser printer. The ink is very expensive. The ink is water soluble and will run if the paper gets wet Highest cost per page of all the printers for producing color documents, it has the highest quality at a reasonable price.
c. Laser printers (non-impact printer) A laser or LEDs make dots on a light sensitive drum. Toner (very tiny particles of plastic) stick to the drum where the dots where made. For black and white printouts, very low cost per page Printout is permanent. Color laser printers are still fairly expensive
iii. Speakers Used to output sound
iv. LCD Projectors Similar to monitors but projects an image on to a screen. They are mainly used for presentations.
Central Processing Unit (CPU)/Processor:
It is the main part of a computer system like the brain of a human being. It interprets the instructions in the program and executes one by one. The CPU of a microcomputer I called a microprocessor. Central Processing Unit is implemented in a single piece of silicon device known as a computer chip.

The processor and main memory of a PC are commonly held on a single board called a mother board. The processor has the following functions:
i. It controls the transmission of data from input devices to memory;
ii. It processes the data held in main memory;
iii. It controls the transmission of information from main memory to output devices.
The processor contains the control unit and the arithmetic/logic unit (ALU).
1. The control unit coordinates and controls all the operations carried out by the computer. The control unit operates by repeating three operations which are:
i. Fetch – cause the next instruction to be fetched from memory;
ii. Decode – translate the program instruction into commands that the computer can process
iii. Execute – cause the instruction to be executed
2. The arithmetic/logic unit (ALU) plays two roles.
i. Arithmetic operations – these operations are addition, subtraction, multiplication and division.
ii. Logical operations – it compares two data items to determine whether the first one is smaller than, equal to or greater than the second item.
Main Memory:
The cycle (input – processing – output) would not be possible without a holding place for the instructions and data that the processors (CPU) can easily reach. This holding place is known as memory also called main storage and is internal to the computer consisting of RAM and possibly ROM.
Random Access Memory (RAM)
Is the basic kind of internal memory that holds data and instructions while the computer is in use. It can be read from and written to. It is called random access because the processor or computer can access any location in memory in any order as contrasted with sequential access devices which must be accessed in order.
RAM is volatile; losing the stored information in an event of power loss, and quite expensive.

ROM (Read only memory)
Is also random access but only for reads, once data has been written onto a ROM chip, it cannot be removed and can only be read. It refers to special memory used to store programs that boot the computer and perform diagnostics. Most personal computers have a small amount of ROM (a few thousand bytes). Retains its contents even when the computer is turned off and is therefore referred to as being nonvolatile.
Secondary storage
These are devices which are used to store huge information for future use. This is mostly hard drives and removable media such as floppy disks, optical media (CD ROM) etc.
i. Hard Drive:
ii. Floppy Disk: Floppy disks allow information to be transported easily from one computer to another they have limited storage capacity, generally 1.44 MB. Saving and retrieving information from a floppy disk is slower than on a hard drive. They are more susceptible to physical damage and viruses than the hard drive. The size of a hard drive is usually expressed in terms of megabytes and gigabytes.
iii. Compact Disk Read Only Memory (CD ROM): CD ROMs are read only storage medium. Typically, a CD ROM holds up to 650 MB of information. While information retrieval is faster than from a floppy disk, it is still not as fast as from the hard drive.
iv. Compact Disk-Writable (CD-R): A CD-R is highly effective for storing a large amount of data. Can hold up to 700MB of information. A CD-R is a one-time recordable compact disc.
v. Compact Disk-Re-Writable (CD-RW): A CD-RW allows you to read, write, erase and write again. Writing takes place in a single pass of the focused laser beam. This is sometimes referred to as direct overwriting and can be repeated several thousand times per disc.


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