Input output devices

Operations:

§  INPUT: This is the process of entering data and programs in to the computer system. The input unit takes data from us to the computer in an organized manner for processing.

§  STORAGE: The process of saving data and instructions permanently is known as storage. The storage unit is the primary storage of the computer system. It provides space for storing data and instructions.

     

 The storage unit performs the following major functions:

§  All data and instructions are stored here before and after     processing.

§  Intermediate results of processing are also stored here.

FUNCTIONAL UNITS:

ARITHMETIC LOGICAL UNIT(ALU):

     

        The actual processing of the data and instruction are performed by Arithmetic Logical Unit.

      

        The major operations performed by the ALU are addition, subtraction, multiplication, division, logic and comparison.

        Data is transferred to ALU from storage unit when required.

        After processing the output is returned back to storage unit for further processing or getting stored.

CONTROL UNIT(CPU):

  

§  The control unit determines the sequence in which computer programs and instructions are executed.

§  Things like processing of programs stored in the main memory, interpretation of

§  the instructions and issuing of signals for other units of the computer to execute them.

§  Therefore it is the manager of all operations mentioned in the previous section.

       CENTRAL PROCESSING UNIT(CPU): 

      

        The ALU and the CU of a computer system are jointly known as the central processing unit. You may call CPU as the brain of any computer system. It is just like brain that takes all major decisions, makes all sorts of calculations and directs different parts of the computer functions by activating and controlling the operations.

       PHYSICAL  COMPONENTS THAT MAKES A COMPUTER:

1.      CPU

2.      MEMORY

3.      DATA BUS

4.      PORTS

5.      MOTHERBOARD

6.      HARD DISK      

7.      I/O DEVICES

Memory systems:

         There are two kinds of computer memory:

                 primary 

                 and secondary.

        Primary memory is accessible directly by the processing unit. RAM is an example of primary memory. As soon as the computer is switched off the contents of the primary memory is lost. You can store and retrieve data much faster with primary memory compared to secondary memory.

        Secondary memory such as floppy disks, magnetic disk, etc., is located outside the computer. Primary memory is more expensive than secondary memory. Because of this the size of primary memory is less than that of secondary memory .

      The following terms related to memory of a computer are discussed below:

ž Random Access Memory (RAM):

ž  The primary storage is referred to as random access memory (RAM) because it is possible to randomly select and use any location of the memory directly store and retrieve data. It is also called read/write memory.

ž  The storage of data and instructions inside the primary storage is temporary. It disappears from RAM as soon as the power to the computer is switched off. The memories, which loose their content on failure of power supply, are known as volatile memories .So now we can say that RAM is volatile memory.

ž Read Only Memory (ROM):

ž  There is another memory in computer, which is called Read Only Memory (ROM. The storage of program and data in the ROM is permanent. The ROM stores some standard processing programs supplied by the manufacturers to operate the personal computer.

ž  The ROM can only be read by the CPU but it cannot be changed. The basic input/output program is stored in the ROM that examines and initializes various equipment attached to the PC when the switch is made ON. The memories, which do not loose their content on failure of power supply, are known as non-volatile memories. ROM is non-volatile memory.

       PROM:

       Programmable Read Only Memory (PROM). You know that it is not possible to modify or erase programs stored in ROM, but it is possible for you to store your program in PROM chip.

ž  Once the programmes are written it cannot be changed and remain intact even if power is switched off. Therefore programs or instructions written in PROM or ROM cannot be erased or changed.

      

       EPROM: 

        This stands for Erasable Programmable Read Only Memory, EPROM chip can be programmed time and again by erasing the information stored earlier in it.

         Information stored in EPROM exposing the chip for some time ultraviolet light and it erases chip is reprogrammed using a special programming facility. When the EPROM is in use information can only be read.

      

       CACHE:  

       Cache memories are accessed much faster than conventional RAM. It is used to store programs or data currently being executed or temporary data frequently used by the CPU.

ž Each memory makes main memory to be faster and larger than it really is. It is also very expensive to have bigger size of cache memory and its size is normally kept small.

       Registers:    

       

        The CPU processes data and instructions with high speed, there is also movement of data between various units of computer. It is necessary to transfer the processed data with high speed.

        So the computer uses a number of special memory units called registers. They are not part of the main memory but they store data or information temporarily.

   SECONDARY STORAGE:

        Often it is necessary to store hundreds of millions of bytes of data for the CPU to process. Therefore additional memory is required in all the computer systems. This memory is called auxiliary memory or secondary storage.

       Magnetic Tape: 

        Magnetic tapes are used for large computers like mainframe computers where large volume of data is stored for a longer time.  Tapes consist of magnetic materials that store data permanently. It similar to cassette tape recorder.

        Magnetic Disk: 

         It rotates with very high speed inside the computer drive. Data is stored on both the surface of the disk. Each disk consists of a number of invisible concentric circles called tracks. Information is recorded on tracks of a disk surface in the form of tiny magnetic spots.

       Floppy Disk:

        It is similar to magnetic dis. The capacity of a 5.25-inch floppy is 1.2 mega bytes whereas for 3.5 inch floppy it is 1.44 mega bytes. The floppy is a low cost device particularly suitable for personal computer system.

Optical Disk:

  

Optical disks can be divided into the following categories:

Compact Disk/ Read Only Memory (CD-ROM):

§   CD-ROM disks are made of reflective metals.

§   Each disk is approximately 4 1/2 inches in diameter and can hold over 600 MB of data.

§   As the CD-ROM can be read only we cannot write or make changes into the data contained in it.

Write Once, Read Many (WORM):

§  The inconvenience that we can not write any thing in to a CD-ROM is avoided in WORM. A WORM allows the user to write data permanently on to the disk.

§  The advantage of WORM is that it can store vast amount of data amounting to gigabytes (109bytes).

§  Any document in a WORM can be accessed very fast, say less than 30 seconds.

Erasable Optical Disk:

        These are optical disks where data can be written, erased and re-written.

         These disks may be used as alternatives to traditional disks. Erasable optical disks are based on a technology known as magnetic optical (MO).

I/O devices:

     INPUT DEVICES:

        Keyboard:

     This is the standard input device attached to all computers. The layout of keyboard is just like the traditional typewriter of the type QWERTY. It contains a total of 101 to 104 keys.

       Mouse: 

      Mouse is an input device used with your personal computer. It rolls on a small ball and has two or three buttons on the top. When you roll the mouse across a flat surface the screen censors the mouse in the direction of mouse movement.

      Scanner: 

      Scanner is an optical device that can input any graphical matter and display it back. The common optical scanner devices are Magnetic Ink Character Recognition (MICR), Optical Mark Reader (OMR) and Optical Character Reader (OCR).

Magnetic Ink Character Recognition (MICR) : 

›     This is widely used by banks to process large volumes of cheques and drafts.

Optical Mark Reader (OMR) : 

›     This technique is used when students have appeared in objective type tests and they had to mark their answer by darkening a square or circular space by pencil.

Optical Character Recognition (OCR) : 

›      This technique unites the direct reading of any printed character OCRs are expensive though better the MICR.

OUTPUT DEVICES:

ž Visual Display Unit: The most popular input/output device is the Visual Display Unit (VDU). It is also called the monitor. A monitor has its own box which is separated from the main computer system and is connected to the computer by cable. It can be color or monochrome.

ž Terminals: It is a very popular interactive input-output unit. It can be divided into two types: hard copy terminals and soft copy terminals. Terminals are also classified as dumb terminals or intelligent terminals depending upon the work situation.

ž Printer: It is an important output device which can be used to get a printed copy of the processed text or result on paper. Depending on their speed and approach of printing, printers are classified as  impact and non-impactprinters