Design Methods


Designing is the first step for obtaining solution for a given problem. The purpose of designing is to represent the solution for the system. It is really difficult to design a large system because the complexity of system can’t be represented easily. So the various methods evolved/ involved for designing.


1) Top-down design

Every system has a several hierarchy of components. The top level component represents the whole system. Top-down design method start from top level component to low level or bottom level components. Then each major component divided into lower level component.


2) Bottom-Up Design

Bottom up design is reverse of top-down approach. It starts from the lowest level components to the highest level components. Every highest level component uses the lowest level components.


3) Modular Approach

It is better to divide the large system into modules. In terms of programming module is logically a well defined part of a program. Each module is a separate part of program. It is easy to modify the program with modular approach, because changes in one module doesn’t affect on the other module of a program. It is also easy to checks the bug in the program with module level programming.





This is interesting to know before learning any language. It is necessary to know, what the basic requirements is and what is the aspects of the computer programmers for any language and also what type of difficulties arises with other language at that time. The language can be classified into two-types:


  • Low level Language
  • High level Language


  • Low level Language
  1. Machine Language
  2. Assembly Language
  3. Machine Language

Computer can understand only digital signals, which is in binary form say 0 or 1. So the instruction given to the computer can be only in binary code 0 or 1. These instructions are called machine level language. Computer can understand only machine level language.

Writing a program in machine language is difficult task, it is not easy for programmers to write the instructions in binary code. Maintaining machine level language program is also difficult. There is possibility for errors in memory locations of binary instructions. Machine level language program is not portable. Every computer has its own instructions, so the programs written for one computer is not portable for other computers.

  1. Assembly Language

In assembly language instructions are given in English like words, such as MOV, ADD, SUB etc. hence it is easy to understand and write assembly programs. As you know computer can understand only machine level language. Hence assembly level language program must be translated into machine language. The translation which is used for translating is called “Assembler”.

In assembly language data are stored in the computer registers. Every computer has different set of registers. As you know machine level language program are not portable so assembly level language program as machine language.

Low level language is related to hardware or with hardware. Hence the execution time of low level language is fast.




  • High Level Language

High level language is designed keeping in mind the feature of portability means these languages program are machine independent. It is easy to understand and easy to write the program of high level language. For translating high level language program into machine level language, compiler, interpreter. The   language in this category is:




C is middle level language which is in between these two categories. Program can be written same as other high level language and it may be possible to interact this with low level language.



Computer can understand only machine language which is in binary form 0 or 1. It is difficult to write and maintain the program of machine level language. So the need arises for converting the code of high level and low level language.



Assembler is used for converting the code of low level language (assembly language) into machine level language.



Compiler is used for converting the program code of high level language into machine language. But it checks the errors of program statement by statement. After checking the one statement, it converts that statement into machine code and then executes that statement. This process is continued until the last statement of program or an erroneous statement occurs so it is useful for debugging purpose.

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