Secondary Memory

Secondary Memory

    The computer system deals with a large amount of data and softwares, to handle various needs.The primary memory has a limited storage capacity and is not permanent.An alternate to this problem is the secondary memory or secondary storage devices.

          Secondary memory is of permanent nature.Data in secondary memory remains there until it is overwritten with new data removed intentionally.They can also be retrieved at any time.Secondary storage devices are of many types and they vary in the capacity and media of storage.They are considered as an auxiliary component and can be attached to the CPU based on the application of the user.

         Earlier secondary memory existed in the form of punched cards, paper tapes, magnetic drums and magnetic tapes.Now the most commonly used secondary devices are magnetic disks and optical disks  

Some Secondary Storage devices :

♠ Magnetic Disks

♠ Floppy Disks

♠ Hard Disk

♠Optical Disk

♠ Compact Disk Read Only Memory (CDROM)

♠ WORM (Write Once, Read Many)

♠ Erasable Optical Disks

♠ Digital Video Disk (DVD)

♠ Magneto Optical Disk

Primary Memory

Primary Memory

        The primary memory of the computer is used to hold two distinct types of information, the data which is to be processed by the CPU and the set of of instruction to be executed next.The primary memory is capable of sending and receiving data at very high speed.The primary memory is classified into two

=>Random Access Memory (RAM)

=>Read Only Memory (ROM)

RAM : 

   

   RAM is used to to store data and instruction needed by the CPU for processing.Data can be stored and retrieved at random from anywhere with the same amount of time, no matter where the data is.Hence the name random access memory .RAM can be used for both reading(retrieving) and writing(storage) of data.So it is also called Read/Write memory.

   Data can be stored in RAM only temporarily because memory is electronic device and hence is of volatile nature.When electronic power is turned off all the contents of the RAM will be lost.CPU requires all the data and instruction under processing to be in the main memory (RAM).So data and instruction should be reloaded  to the main memory every time when the computer is turned on.

   RAM was one of the most expensive computer component to manufacture for many years.Vacuum tubes, transistors and magnetic cores were used in earlier times as memory.However with the invention of semiconductor technology the cost of manufacture and size of memory has drastically reduced.Today the usage of silicon chips has greatly increased the memory capacity of computers.Based on the characteristics of the electronic circuits, RAM exist in various forms like Static RAM, Dynamic RAM (DRAM), Synchronous Dynamic RAM (SDRAM).

ROM :

   Read only memory is a memory unit that can perform only read operations. it does not support storage or write operations.Binary informations stored in ROM are permanent nature and they are stored in the ROM chip at the time of manufacture itself.Hence ROM is of non volatile nature i.e., contents are not lost even if power is turned off.However components connected to the systems perform some basic input/output operations, initiates loading of software that are essential for the working of the computer system.ROM chip is also called Firmware because these instruction are permanently stored in it at the time of manufacturing.

     

     There are exists another three categories of ROM used in some computer system namely

=> PROM (Programmable ROM)

=> EPROM (Erasable Programmable ROM)

=> EEPROM (Electrically Erasable Programmable ROM)

Functional Units of a Computer

 Functional Units of a Computer

          The hardware of the computer system is a collection of electronic circuits and other devices.There are certain basic components or building blocks that exist in all computer system.These components are the Central Processing Unit (CPU), Memory, Input devices and the Output devices.A systematic interaction between these components is essential for the functioning of the computer.

Central Processing Unit (CPU)

    The CPU is referred to as the brain of the computer.The CPU controls the overall functioning of a system.It is the part of the computer where the actual processing of the data by taking input device , storing data in the memory and retrieving them when needed and directing the processed data  to the output device.The CPU comprises of  three parts

     => Arithmetic Logic Unit (ALU)

     => Memory 

     => Control Unit

(Click on topics for more info)

The other Functional units of computer are :

 ◘  Input Unit

 ◘  Output Unit

Computer Memory

                   Just like humans, computers rely a lot on memory.They need to process and store data, just like we do.However computers store data in digital format, which means the information can always be called up exactly the way it was stored.Also, unlike our memory computers memory didn't get worse overtime.While memory can refer to any medium of  data storage, it usually refers to RAM or Random access memory.While your computer boots up it loads the OS into its memory, or RAM.This allow your computer to access system function such as handling mouse and keystroke, since the event handlers are all loaded into RAM

                  RAM is a very high-speed type of memory, which make it deal for storing active programs and system process.It is different than Hard disc space  in that RAM is made up of physical memory chips, while hard disc are magnetic discs that spins inside a Hard drive.Accessing RAM is much faster than accessing the hard disc because RAM access is based electric charges, while hard drive need to seek to the correct part of the disc before accessing the data.However all the information stored in RAM is erased when computers's power is turned off..The hard disc on the other hand, store data magnetically without requiring electrical power.Another common type of memory is Flash memory, which is typically used for small devices such as Digital cameras, USB key-chain drives and portable music player like the iPod nano.This kind of memory, known as ' EEPROM ' or electrically erasable programmable read-only memory is convenient for portable devices.Since it stores information even its power source is turned off, but is smaller and more resilient than a Hard drive.To summaries, memory is the vital part of computers and other electronic devices to function.

The computer memory is mainly classified into two :

♣ Primary Memory

♣ Secondary Memory


(click on topics for more info)

Output Unit

Output Unit

           Output devices are used to communicate the processed information to the user.The results of the processing operation in machine readable form must be made available in a human readable form.The output devices translate processed data in machine readable form to s form that can be interpreted by humans.The most common types of output devices are Monitors, which resembles the television screen and printer, which copy from the computer onto paper.Outputs can be obtained in the form of drawings and voices.

Output Devices :

           To be effective, information must be produced in an usable form.An output device is any machine capable of representing information from a computer.Output devices can be divided into 2 : (i) Hard copy devices : Output is in direct usable form.They produce a permanent record on paper. (ii) Soft copy devices : Produce output that cannot be used directly.They do not produce a permanent record.Hard copy devices are slow compare to soft copy devices.Some hard copy devices are printers, plotters, etc.Examples of soft copy  devices are Visual Display unit (VDU),Liquid Crystal Displays(LCD), etc.

          Output devices are also classified as commonly used(VDU, Printers) and special purpose devices(Plotters, LCD, etc).

Input Unit

Input Unit

           The input devices are used to enter data to the computer system.There are many types of input devices depending on the nature of data to be entered.Key board is one of the most commonly used input device.It is used for alphanumeric data entry.Mouse is another common input device used to locate screen positions.There are also unusual input device that respond to voices and touch.The input device is also responsible for translation of data to a form that the computer system can understand

Input Devices :

         An input devices is any machine that is used to feed into the computer.Some of them are general purpose, that is they are used by all computers where as some others are special purpose which are used to input data in a specific way.Key board and Mouse can be considered as general purpose and special purpose input devices are optical mark readers, optical character readers, optical character readers and track ball.

Computer as a System

  Computer can be considered as a device made up of a combination of electronic and electromechanical components.As any other devices computer by itself has no intelligence.A computer comes to life only when it is connected to some other components .The computer along with these components make it a system - Computer System.

 The computer system is a combination of basically five elements.

♣ Hardware

♣ Software

♣ Users/People

♣ Procedures

♣ Data/Information

Hardware
   The physical equipments and components which one can see, touch and feel(tangible components) in a computer system are called hardware.

Software
  The instructions that tell the hardware how to perform a task is called software.The hardware does not know what to do without these instruction.

Users
   Users or people are considered as the most important of the computer system.They operate the hardware, create, the instructions to perform a particular task i.e., software, responds to present and coordinate the data     and information flow.

Procedures
   Procedures are the steps to be followed while a particular task is being performed using the computer system.These procedures may be documented or guided by the software that perform the task.

Data/Information
   The prime objective of a computer system is data processing.Data are raw, unevaluated facts and figures, concepts or instruction.This raw material is processed into useful information.Information is the product of data processing.

Connectivity
   A computer system as such can be set up to communicate with another computer system.The media used to connect the two systems like phone lines, artificial satellites, microwave stations are also considered as an element of the computer system.

Computer Language

Computer Language 

    Computer Languages are means of giving instruction to the computer .They are classified into two types :

    ♦ High Level Language (HLL)

    ♦ Low Level Language (LLL)

High Level Languages (HLL)

   

        Instructions and expressions written in English like languages is known as High Level Languages.High Level Languages are designed to make programming very easy.That is all the instructions in HLL can be easily understood by any Human being.Some of the HLL are , COBOL, PASCAL, BASIC, FORTRAN, C++.

Low Level Languages (LLL) 

       Low Level Languages are classified into 2 types (1) Assembly Language (2) Machine Language.Machine Language is the Binary language (0's and 1's) which is the only language understood by the computer.In assembly language programs are developed using codes.Machine Language is very easy complex and it takes time to write.So  programs were developed using coding which can be remembered easily.For adding two numbers it uses  ADD.In this language we can use numeric codes for writing programs.

The languages written in Assembly languages and HLL are translated using Language processors.

Computer Softwares

"Computer Softwares are collection of programs designed for a particular task"

Softwares are classified into two :
1) System Software
2) Application Software

■ System softwares are again classified into two types(Click on 'System softwares' for more information)
■ Application Softwares are two types(Click on 'Application softwares' for more information)

Softwares give instructions to Hardwares for doing particular tasks.

Computer Hardware

What is a Hardware ?

" The parts of computer which can touch, see and feel are called Hardwares ".Hardwares and Softwares together form a Computer System.

Below are a list of Hardwares which is often seen in PC :

1) Motherboard

2)Monitor 

3)Keyboard

4)Mouse

5)PC case

6)Power supply

7)Hard Disc Drive[HDD]

8)Floppy Disc Drive[FDD]

9)Compact Disc Drive[CDD]

10)Speakers

11)Headset

12)Digital Video Disc Drive[DVD(D)]

13)Wires and Cables

Hardwares are instructed by Softwares for performing particular task.