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Why assembler programming ?

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• Different way to program a computer
  • Instructing a computer to do stuff for you:

    Humans use languages to instruct a computer to "do stuff" for them....

  • The are different programming languages:

    High level programming languages: High level programming languages are designed to help programmers to easily write correct algorithms on any computer Examples: Java C/C++              Low level programming languages: Low level programming languages are designed to let programmers take control over every component in a specific computer Example: Assembler programming language            Comment: Viruses (at least a part of the virus) are written in assembler programming language !!!

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• Feature of a high level programming language
  • Recall:

    High level programming languages are designed to help programmers to easily write correct algorithms on any computer

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  • To achieve this goal, high level programming languages provide:

    Programming constructs such as: Variable definitions Assignment statements If-statements Loop- statements Methods and so on Access protection for variables, such as: Scoping rules for local variables private and public access specifiers And so on.... Automatic type conversions when the conversion is safe Examples: byte ⇒ short short ⇒ int byte ⇒ int .... float ⇒ double ...

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• Feature of an assembler programming language
  • Recall:

    Assembler programming languages are designed to let programmers take control over every component in a specific computer Warning: It is uncomfortable to write assembler programs !!!! (Because the ease provided by a high level programming language (such as Java) is not available !!!!

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  • To achieve the above goal, assembler programming languages:

    consist of commands to tell a computer to perform a certain instruction Example: Add Subtract Jump (explain later what this is)           and so on can access any component inside the computer Sample components: Any memory location (virus alert !!!) Registers inside the CPU and so on. are specifically designed for one (type of) computer !!! A program written in assembler program language for computer A will not work on any other (type of) computer !!!

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• Differences between high level and assembler programming
  • Important difference between high level programming language and aasembler programming language:

    High level programming languages have features to: Prevent a programmer to access certain variables (e.g.: private) Automatically insert instructions into a program to perform some safe conversions Example: int i; short s; i = s; // Java will automatically convert // the short data type in s to int data type // before assigning the int value to i An assembler programming language is "what you see is what you get" !!! The assembler programming can access any thing inside the computer There is nothing that can prevent an assembler programmer to do any thing with the computer !!! (You have complete control (power) over the computer --- but with more power comes more responsibility !!!) There are no "automatic" stuff done for your "convenience" You are responsible for making sure that operations are performed using the correct data types !!!!

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• Why program in assembler ?
  • Powerful:

    When you program a computer using assembler code, you are instructing the computer directly. You can do anything you want (granted, you have to know what you're doing first !)

    Disadvantage of assembler programming:

    It is very "uncomfortable" (= difficult) to write correct assembler programs

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  • General practice:

    Use high level programming language as much as possible (programs are easier to write and maintain) Functions that (1) cannot be coded using high level programming languages or (2) must be highly optimized, are written in assembler (Methods/functions written in high level programming language can interact (can invoke one another and pass parameters) with functions written assembler programs - we will see this later in the course)