Computer Science CBSE class 11 chp-14

( This is a brief note of chapter 14 , 2 and 4 . Here only main points are given . Study each topic ‘s explanation from textbook . for example :- Here “Characteristics of a good program “ ..its main points like reliable , portable ….etc is given . but you should study what is reliable ? and …what is portable …? . ie its explanations from textbook . )

Chapter - 14 Programming methodology

 Software design’s main goal is user satisfaction.  s/w designing consists of 2 parts:  program structure:-it refers to how a program should be  programrepresentation :-it refers to its presentation style so that the program becomes more readable and presentable.  If a program presenting in a good style will minimize  Wastage of time  “ effort  “ cost  Guidelines Meaningful names for identifiers 1. Assign meaningful names for all identifiers viz. variables and functions 2. Do not use similar looking names eg:- manage ,manager Ensure clarity of expression  It must be clearly understood by the user  Avoid programming tricks  Never sacrifice clarity of expressions  Use standard functions in expression to enhance readability Use comments and indentation  In c++ comments are either // or /* * /

1. Always insert prologues:- summaries the purpose of the program 2. Insert explanatory comments  Indentation makes the statements clear and readable  Always indent statements :- ie highlight nesting of groups of stmts Insert blank lines and blank spaces Statement formatting style  Free formatting style :  Prettyprinting :- when program formatting is done to make a program more readable , it is called prettyprinting. Characteristics of a good program 1) 2) 3) 4) 5)

Effective and efficient User friendly Self – Documenting code Reliable Portable

Robustness  The ability of a program , to recover following an error and to continue operating within its environment is called robustness Guard code  The code which can handle exceptional data errors and operational errors is called guard code Types of Errors  Bug: An error of a program is called bug  3 Types of errors: Compile time errors  Run-time errors  Logical errors Compile time errors

 Occurs during compile time 1) Syntax errors : ? and eg:2) Sematic errors: ? and eg:3) Type errors: ? and eg:Run time errors  Occurs during execution of a program  Run time errors stop the execution , this is called program” crashed” Or program “abnormally terminated” Eg:Logical errors  Program does not provide correct result  Because of programmer’s mistaken analysis of the program Problem solving Techniques 1) Understand the problem well To create a new pgm or improve an existing one, we must recognize that problem. ( check need any improvement ? OR what is required or desired for the proposed s/m ?) 2) Analyze the problem It involves identifying the program specification and defining program’s minimum no.of Input required for output, and processing components 3) Design programs Develop the steps to solve the problem. ie sequence of steps that solve a given problem are called Algorithms. Break down the solution into simple steps.(Top –down design :- Firstly list sub-problems and then the original problem is solved by solving each of its sub-programs.) 4) Code the program Coding is the technical word for writing the program. This step is to translate the algorithm into programming language.( using appropriate control structures such as conditional and looping control structure ) 5) Test and debug programs Testing is the process of finding error in a program . Debugging is the process of correcting errors found during the testing process. 6) Complete the documentation Written descriptions of a program , which makes a program more readable ,understandable and easily modifiable. 7) Maintain programs It means modify the pgms. To enhance pgm’s functionality keep up- to- date with Govt regulations

Program maintains  Program maintenance refers to modification of a program  Four kinds of maintenance : Corrective maintenance After program compilation , some errors might show up. To correct this type of errors are called corrective maintenance.  Adaptive maintenance Changes in environment likes new govt. laws and regulations , company policies may change are also may lead to system maintenance.  Preventive maintenance If possible errors could be anticipated before they actually occur . It will reduce system down time . This type of maintenance is called Preventive maintenance  Perfective maintenance IT is the fastest growing area. ie depends up on technology changes , In the existing system , should add new features and capabilities . It is called Perfective maintenance. ________________________________________________________ Chapter 4 I/p O/p and Memory Devices Input Devices  …….? Output Devices  …..?

Memory Devices  Memory is used to store data and instructions  Memories can be read from and write into.  Read –write memories:-can be read from and written into

Read only memories:- program or data permanently stored.  Two types of memory : Primary memory ( main memory)  Secondary memory Primary memory  It has limited storage capacity and is not permanent . It can be divided into two : RAM ( Random access memory )  ROM ( read only memory ) RAM  RAM refers to random access memory where both read and write operations can takes place.  RAM is volatile memory , its contents are lost when the power is turned off.  2 types of RAM: DRAM:- …?  SRAM:…. ?  ROM  It refers to read only memory where read operation can takes place.  It is non- volatile memory , not lost data it is permanent  2 Types of ROM : PROM :- programmable read only memory . This can be programmed once . A PROM programmer write own data and programs in it  EPROM :- Erasable programmable read only memory . It can be erased as well as reprogrammed Secondary memory  Secondary storage devices are used to store large amount of data permanently .  Common storage devices are: Hard disk magnetic disk

   

Floppy disk CD ROM (CD-R and CD_RW) DVD ( DVD– R and DVD – RW) Blu – ray Disk ….?

optical disk

Flash memory or USB memory  Pen drive / Thumb drive …? Bluetooth  …? Serial and parallel ports  ? Cache memory  It is a special high-speed storage mechanism that stores most recently accessed data .It makes the CPU run faster if the required data is found in cache.  Two types of cache memory : Level 1 (L1) cache  Level 2 (L2) cache ___________________________________________________________________ Chapter 2 Operating System  Types of software  System s/w  Application s/w System s/w OS Language processor Application S/w Packages :- Word , Spreadsheet , DBMS , Graphics ,multimedia and presentation S/Ws

Utilities :- Antivirus , Backup utility, compression utility, Disk defragmenter Customised S/w :- Billing s/ws…….

 OS :- An Os is a system software which act as an interface between a user and the hardware ( ie. All computer resources )  It is a an important component of a computer s/m which controls all other components of the computer Types of OS ( study the explanation of each OS from Text book )      

Single program OS:Multiprogramming OS Time Sharing OS Real Time OS Multiprocessing OS Interactive OS

Need of OS  Primary goal :- To make the computer system convenient to use  Secondary goal :- To use computer hardware in an efficient manner Types of Services      

Program execution Handling input/output operations Manipulation of file system Error detection and handling Resource allocation Information and resource protection

OS Functions  Processor Management  Memory Management ( storage )  File and device Management ( Information management ) Processor Management

 what is processor management ?  job scheduling ?  Two types of scheduling  preemptive scheduling  non preemptive scheduling  Explain about preemptive scheduling ?  Explain about non preemptive scheduling ?  Explain about FCFS ,SJN ,Deadline , Round Robin scheduling techniques ? Memory Management ( storage )  How OS managing the memory .? File and Device management  How OS managing the file and device