Operating System and Safeguards



The operating system must provide various safeguards:
=> Safety from accidental or malicious access by other users.
=> Safety from accidental damage caused by the owner of the files.
=> Access limited to either the owner of the files or a specified user or group of users.
=> Safety from hardware or software malfunction.

These safeguards can be achieved through:
=> The use of passwords.
=> Allowing the owner of the files to specify which other users may access his file.
=> Mode of access being specified - read only, write, append.

Logging: The OS also keeps a log of all the system actions that relate to a particular user's job. It also maintains a log of all the jobs that are run at larger computer systems. These jobs are clocked in and out of the system. In instances of program failure, this log helps in locating the causes of program failure.

System Scheduling: Multiple tasks are scheduled to balance input/ output and processing requirements. This often involves overlapping input/ output and processing operations. The operating system allocates specific areas of storage to each program. When a program is completed the remaining programs are re-positioned in storage and a new program or programs are added to take up the available space.

Monitoring System Status: The OS constantly monitors the status of the computer system during processing operations.

=> It may respond to user "help" commands, and supply information about its function and operation.

=> It also directs the computer to send messages to the operator's terminal when I/O devices need attention, when errors occur in the job stream, or when other abnormal conditions arise.

=> In a larger computer system, the computer does not wait for the operator to take appropriate action. Rather, the message is printed and control passes to the next job.

Multi-Access Control: In larger computers the processing power can often be utilized more efficiently if a number of individuals are able to access them at the same time. With these multi-user systems, the OS
=> Allocates limited CPU time among users.
=> Separates job requests.
=> Must avoid mix-ups.

Software Utilities: These are programs or routines which carry out certain procedures which are common to virtually all applications.

Utility software performs needed services such as
=> Sorting records into a particular sequence for processing.
=> Merging several sorted files into a single large updated file.
=> Transferring date from one I/O device to another.
=> Printing of files held on backing storage.
=> Printing the contents of main memory.

Translating Programs: Translating programs trans-form instructions written in humanly convenient form to machine language codes required by computers. These translating programs are loaded into the computer where they control the translating process. Compilers and interpreters are used to translate programs to machine language codes.

Compiler: A compiler translates a program written in a high-level language to executable machine instructions. The compiler treats source-program instructions as data. Each instruction is accessed in turn and translated into one or more lines of object code in machine language.

Interpreter: Some high-level programming languages often use an interpreter instead of a compiler to translate instructions into machine code. Instead of translating the source program and permanently saving the object code produced during a compiling run for future use, the source program is loaded into the computer along with the data to be processed. When a program is to be executed, the interpreter accesses only the first instruction, translates it into one or more lines of machine code and then if possible the instructions are executed. The interpreter then accesses the next instruction and the process is repeated. This process continues until all the source program instructions are translated and executed.

Application Programs: An application program is designed to handle a particular task required by the end-user. It handles all aspects of a routine application, including error situation, the display of menus to aid the user, thus making it possible for a user having very little computer expertise to process the application.

Multiprogramming and Multiprocessing

Multiprogramming: Multiprogramming is the process of combining hardware and software to create a situation in which more than one program may be held in main store at any one time. It is thus possible to process several tasks simultaneously. The main objective is to minimize unused CPU time.

Multiprocessing: Multiprocessing is the execution of two or more different programs at the same time.

Typically, in multiprocessing, multiple CPUs sharing a common memory are used. Instructions from different and independent programs can be processed at the same instant by different processors. On the other hand, the processors may simultaneously execute different instructions from the same programme.

Loosely Coupled Multiprocessing: In it a collection of relatively autonomous systems are used. Each CPU has its own main memory and input/ output channels.

Functionally Specialized Processors: Such as an I/O processor. There is a master, general-purpose CPU. Specialized processors provide services to the CPU and are controlled by it.

Tightly Coupled Multiprocessing: In it a set of processors share a common memory.
They are controlled by the operating system.

Parallel Processing: They are tightly coupled multiprocessors that can execute a job in parallel.

A number of desirable features of a comprehensive operating system are:
=> Job control language
=> Failure and recovery
=> File security
=> Logging
=> Scheduling
=> Monitoring system status
=> Multi-access control

Job Control Language: During the processing of application programs, the operating system provides automatic job-to job linkages. These linkages are handled by a job control program. In some systems macro commands (macros) may be used to supplement the command language. The macros can be either system or user defined.

Failure and Recovery: Invalid conditions and fault conditions cause interrupts to be raised, to signal the operating system.

The operating system is called in if, for example.
=> An invalid instruction is encountered in program.
=> A program attempts access to storage areas reserved for another.
=> An overflow occurs in allotted storage area during arithmetic calculations.

According to its instructions, the operating system may either halt the process and signal the operator or switch control to error recovery routines provided by the user.

Dumping: It is a facility whereby all the contents in specified storage areas are written out as output.

File Security: The security of the system may also be monitored. Any attempt to use unauthorized passwords from on-line terminals may be recorded.

It is possible for files to be either private to a particular user or to be shared by a number of users under flexible controls.


Software and Operating System



Software: Software is the part of the computer system which enables the hardware to operate.  Computer software can be divided into two major classifications:
=> System software
=> Application software
         
System software includes the computer programmes that run a computer system itself or that assist a computer in running application programmes. It also includes the documentation that describes how these programs operate. System software consists of:
=> Operating system
=> Utilities.

Operating System: An Operating System (OS) is an integrated set of specialized programs which permit the continuous operation of a computer from one program to the next with minimum amount of operator intervention.

Through the OS the computer can supervise its own operations by automatically calling in the applications programs, translating any other special service programs, and managing the data to produce the desired output.

Types of Processing Systems

Batch Processing System: In batch processing, data are gathered from time to time and collected into a group or batch before they are entered into a computer system and processed. When batch processing is used, the input data are typically recorded on source documents before being converted into a machine-readable form.

On-line Systems: An on-line system is one in which the system interacts directly with the user. As soon as the user inputs data, it is processed immediately. The system validates data at various points, and ensures that correct data is being entered.

Real-Time Processing: Real-time systems are on-line systems with tighter constraints on response time. In these systems the data is processed and results are generated fast enough to influence on-going activity.

Time Sharing: As its name implies, it has the ability to process several tasks simultaneously. In the time-sharing mode, the computer switches from one job to the other at a rapid rate. The jobs are entered into the computer through different terminals connected to the computer by cables. After processing the first user's job, it proceeds to the second and then the third, for short bursts of time or 'time slices' before returning to the first user's job from where it was earlier suspended.

This cycle continues indefinitely: when one programme is finished it is replaced by another one.

Integrity, Fallback and Recovery: With any system whether batch, on-line, or real-time, there is a danger that the system might break down. Certain procedures need to be followed to ensure that data is not lost, or the exact amount of data lost is known.

Integrity: Features of the systems which make it less likely to fail, are classified as 'integrity'. This is the most vital part, since system crashes may result in the loss of data and time.

Fallback: There are some procedures which have been created for use when the system fails, e.g. in some airlines enquiry systems, when the system fails, the fallback procedure allows the terminals to keep collecting data, though without validation. This allows some work to go on even though the main computer is down.

Recovery: This is the process of bringing back the computer into full use when the system fails. It involves bringing back the data, i.e. restoring the data back to the stage it was in before the break down.

File Organization

For information to be useful it should not only be recorded, but it should also be easy to access and retrieve the information. File organization may be:
1.  Serial
2. Direct access
3. Indexed sequential access

Serial Organization: In serial file organization, records are held and accessed in a predetermined sequence of keys. Records can be organized in numerical, alphabetical or chronological order.

Direct Access Organization: Direct access files are stored on magnetic disks or other devices where each record is assigned a physical address.

Indexed Sequential Access: The computer records of an indexed sequential file are stored in the main storage portion of the file, which is divided into sections called segments. Usually, all segments are the same physical size e.g. one cylinder.



Files and Systems



Computer Files: It is convenient to store similar information together and this is the idea behind both manual and computer files.

Data Field: The smallest unit of data is the data field. The data field consists of a group of related characters treated as a single entity.

Record: A collection of related data items treated as a single unit is called a record.

File: Records are grouped to form files. A file is a number of related records that are treated as unit representing a particular transaction.

Master File: Master files are perpetual files, i.e. apart from the time of their creation they are never empty. Further, they maintain information that remains constant over a relatively long period of time. When the information changes the master file may be updated. The normal methods of updating are by adding, deleting or editing records in a file.

Transaction File: Transaction files are files in which data prior to the stage of processing is recorded.

The data in transaction records may be collected automatically or may be initially recorded on source documents and later converted to machine-readable format.


Main Input Devices of Computers


The following are the main input devices:
a) Keyboards:
The key board resembles a typewriter. But there are additional keys that handle control functions. The computer keyboard has three categories of keys.
=> Alphanumeric keys 
=> Special key
=> Function keys    
The Alphanumeric Keys comprises of alphabets (A-Z or a-z), numbers (0-9) and other characters, like space, ./ × ' ; : — ~ ! @ # $ % ^ & * ( ) - + = | \ { } [ ].

The Special Keys perform specific tasks. Some of the special keys are, Enter or the Return key, Backspace key, Del key, the Ins key, Shift keys, e Caps lock key, Num Lock key, Ctrl key and the Alt key.

The Function Keys are used to perform a set of operations by a single keystroke. The function keys can be used for various functions. They can be used as short hand for a sequence of keystrokes, configured accordingly.

Mouse: One of the most popular types of specialized input devices for terminals or micro computers is a mouse. Which is used as a pointing device, the mouse is a small box, about the size of a tape cassette with a round ball on the bottom and one or more buttons on the top. The mouse is attached to a terminal or micro computer by a cable. A mouse enables the user to manipulate a pointer or an arrow on a terminal or micro computer screen.
Joystick: Joysticks are designed in the shape of handles that swivel in 360 degree arcs, enabling their users to control screen figures.
Its utilization for commercial data processing applications is limited.  

Barcode Reader: Data can be coded in the form of light and dark bars with coded spacing’s and thickness. These are called barcodes which are commonly used to identify items. Each item is labeled with a Universal Product Code (UPC). The code is read by a wand or pen which transmits a laser beam and receives the reflection from the label. These pulses are compared with standard codes stored in the computer. A barcode is commonly seen on the back of any book published in recent times.
 

OMR: The Optical Mark Reader (OMR) is a device which can detect the presence or absence of a mark on a paper. Light is incident onto the paper and the reflected light is detected. The presence of a mark is detected due to intensity of light being reflected from the mark. OMR is used in reading answer sheets, questionnaires.
OCR: Optical Character Reader (OCR) is an improvement over OMR. This can not. Only detect a mark but can also recognize its shape and identify characters directly from source documents. The amount of light reflected differs depending on the shape of the character and the OCR can detect and interpret these minor differences.  
MICR: Magnetic Ink Character Recognition (MICR) systems use special ink which can be magnetized, to print characters that can then be read and decoded by special magnetic devices.
This system is widely used by banks for processing cheques. The cheque number, the bank and branch code and the account number are printed with ink containing magnet sable particles of iron oxide.


Functional Components of Computer





Functional Components:
The hardware of a computer system can be classified into the Central Processing Unit (CPU) and peripherals.
The heart of the computer is called CPU or Processor.

The CPU Performs:
I) Arithmetic Operations
II) Logical Operations
III) Input-Output Operations
IV) Internal data movements (moving data between various parts of storage)
V) Data manipulation

To perform these operations the CPU has various components:
    
a. Arithmetic-Logic Unit (ALU): It performs the actual calculations (addition, subtraction, division, multiplication) and comparison (equal to, greater, lesser, positive, negative, zero etc).
    
b. Control Unit (CU): It coordinates the operation of the hardware, the flow and execution of data and instructions that are fed into the memory or main storage via the CPU.

c. Memory Unit (Main Store): It holds data instructions (that are being interpreted and executed), intermediate results and final results ready for output. The data and instructions are passed from the main store into ALU, or to and from the storage devices under the control of the CU.
          
Within the CPU there are a number of high speeds, special purpose memory units called registers. These registers carry out critical functions in the execution of programmes.

A computer has four basic types of registers:
1) Accumulator register (ACC)
2) Store operand register (SOR)
3) Control register (CR)
4) Instruction address register (IAR).

Buses: The control unit and internal storage are linked together by sets of parallel electrical conducting lines called buses. The buses that carry data are called data buses. The retrieval of data from memory is carried by the memory address bus.

Peripheral Devices:
The peripheral devices can be classified as input devices, output devices and backing storage devices.

Input Devices allow the user to get data into the machine. A large range of input, devices are available, e.g. keyboard, mouse.

Output Devices are peripherals used to output results to the user. They include printers, plotters and VDUs (Visual Display Units).

Backing Storage Devices or the secondary storage devices are mainly hard disk, CDS, disk packs, floppy disks, and tapes used to store data and programmes permanently.

Digital Computer



Computer: A computer is a device that computes or calculates numbers. A computer, however, does more than that. It can edit text, generate pictures or graphs, make animation, translate language and even play games or drive motorcars etc.

Computer System: A system is a set of components that works together to accomplish one or more common goals. A computer system can be said to be a system of three major components.

A. Computer Hardware: It includes all mechanical, electrical or electronic parts or components of the computer.
    
B. Computer Software: This includes operating system programmes or applications that instruct a computer how to process the data and generate required information.
    
C. Computer Personnel: People who prepare data for computerized input write computer programmes, monitor computer operations and distribute the output. There are also end users who use computer resources.


Computer Awareness Test-2



Test Your Knowledge
This is a test of your knowledge. You’ll find the answers at the end of the quiz. Please put your scores in the Poll and in Comments. You can also put suggestions for improvement in Comments.
1. What is HTML?
  1. It is developed for World Wide Web (www).
  2. Used for all the formatted documents.
  3. To make formatted web documents with links, those can be viewed in Web Browser.
  4. All of the above
  5. None of these
2. Which of the following is not an input device?
  1. Keyboard
  2. Monitor
  3. Joystick
  4. Microphone
  5. None of these
3. You can keep your personal files/folders in
  1. My folder
  2. My documents
  3. My Files
  4. My Text
  5. None of these
4. The server on the internet is also known as a:
  1. Repeater
  2. Host
  3. Gateway
  4. ISP
  5. None of the above
5. What is the name of the list that stores the URLs of web pages and links visited in the past few days?
  1. Link list
  2. Page list
  3. History list
  4. List
  5. None of the above
6. You click at B to make the text.
  1. Italics
  2. Underlined
  3. Italics and Underlined
  4. bold
  5. None of these
7. Size of the Primary memory of a PC ranges between____________
  1. 2 KB to 8 KB
  2. 64 KB to 256 KB
  3. 20 KB to 40 KB
  4. 256 KB to 640 KB
  5. None of these
8. A Web site's main page is called its
  1. Home Page
  2. Browser page
  3. Search Page
  4. Bookmark
  5. None of these
9. Analog computer is
  1. a means of communicating with at a low level
  2. a device that operates on data in the form of continuously varying physical quantities.
  3. an algebraic high level language
  4. All of the above mentioned
  5. None of these
10. Word’s Count feature
  1. provides information about the number of words in the document
  2. is useful when the length of the document is limited to some number of words
  3. also displays the number of pages, characters, paragraphs and lines in the document
  4. All of the above
  5. None of the above
11. The meaning of Cut is
  1. To take a selection from the document and move it to the Clipboard.
  2. To cut a document in two unequal parts.
  3. To cut a document in two equal parts.
  4. Only b and c above are correct.
  5. None of these
12. A directory within a directory is called
  1. Mini Directory
  2. Junior Directory
  3. Part Directory
  4. Sub Directory
  5. None of these
13. Gopher displays a set of resources on the Internet in the form of
  1. Lists and menus
  2. Options
  3. icons
  4. Both (2) and (3)
  5. None of the above
14. A central computer that holds collections of data and programs for many PCs, workstations, and other computers is a(n)
  1. Supercomputer
  2. minicomputer
  3. My Files
  4. server
  5. None of these
15. A Browser is a
  1. tool for creating a database
  2. software program to view web pages on the Internet
  3. printing device
  4. software program to delete a folder
  5. None of the above
16. Help Menu is available at which button?
  1. End
  2. Start
  3. Turnoff
  4. Restart
  5. None of these
17. Computers built before the First Generation of Computers were:
  1. Mechanical
  2. Electro-mechanical
  3. Electrical
  4. All of these
  5. None of the above
18. ___________ means to enlarge a window to its maximum area so that it will full entire desktop.
  1. Maximize
  2. Zoom
  3. Enlarge
  4. Extend
  5. None of these
19. Which of the controls the manner of interaction between the user and the operating system?
  1. user interface
  2. language translator
  3. platform
  4. screen saver
  5. None of these
20. We can open two database at a time
  1. True
  2. False
  3. Sometimes
  4. Can’t say
  5. None of the above
21. Read Only Memory is permanently ________ in computers.
  1. Input
  2. Tapped
  3. Sealed
  4. Manufacture and control
  5. None of these
22. MOS stands for ________
  1. Most Often Stored
  2. Metal Oxide Semiconductor
  3. Method Organised Stack
  4. All of the above
  5. None of these
23. Formatting toolbar is applied to
  1. select paragraph only
  2. select characters only
  3. select both characters and paragraphs
  4. select whole document only
  5. None of the above
24. The maximum Zoom percentage in MS-Power Point is:
  1. 100%
  2. 200%
  3. 400%
  4. 500%
  5. None of these
25. Data that is copied from an application is stored in the
  1. Driver
  2. Terminal
  3. prompt
  4. Clipboard
  5. None of these
Answers of Computer Awareness Test-2
1. (1) it is developed for World Wide Web (www).
2. (2) Monitor
3. (2) My documents
4. (3) Gateway
5. (3) History list
6. (4) bold
7. (4) 256 KB to 640 KB
8. (1) Home Page
9. (2) a device that operates on data in the form of continuously varying physical quantities.
10. (5) All of the above
11. (1) to take a selection from the document and move it to the Clipboard.
12. (4) Sub Directory
13. (1) Lists and menus
14. (4) server
15. (1) tool for creating a database
16. (2) Start
17. (2) Electro-mechanical
18. (1) Maximize
19. (1) user interface
20. (2) False
21. (1) Input
22. (2) Metal Oxide Semiconductor
23. (3) select both characters and paragraphs
24. (3) 400%
25. (4) Clipboard

Charles Babbage



           Charles Babbage
Charles Babbage another genius in history of computing made a machine called differential engine which could value accurately algebraic expressions and mathematical table correct up to 20 decimal places. Later on he was able to develop analytical machine which was an automatic computing machine designed to do assertions at the rare of 60 per minute and had memory also. His idea of using cards was derived from the work of Joseph jacquard that in France used punched cards to determine the threads to be selected in weaving partners automatically.


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