Lecture%2003%20-%20Bits%20Bytes%20and%20Data%20Types

Lecture%2003%20-%20Bits%20Bytes%20and%20Data%20Types -...

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Copyright @ 2008 Ananda Gunawardena Lecture 03 Bits, Bytes and Data Types In this lecture Computer Languages Assembly Language The compiler Operating system Data and program instructions Bits, Bytes and Data Types ASCII table Data Types Bit Representation of integers Base conversions 1’s compliment, 2’s compliment and negative numbers Variable and storage classes – static, register, auto and extern Functions – pass by value, pass by reference Reading and Writing files Exercises Computer Languages A computer language is a language that is used to communicate with a machine. Like all languages, computer languages have syntax (form) and semantics (meaning). High level languages such as Java are designed to make the process of programming easier, but programmer typically has little control over how efficient the code will run on the hardware. On the other hand, Assembly language programs are harder to write but are designed so that programmer can optimize the performance of the code. Then there is the machine language, the language the machine really understands. All computer languages are designed to communicate with hardware at the end. But programs written in high level languages may go through many steps of translations before being executed. Programs written in C are first converted to an assembly program (designed for the underlying hardware), which then in turn is converted to the machine language, the language understood by the hardware. There may be many steps in between. Machine language “defines” the machine and vice versa. Machine language instructions are simple. They typically consist of very simple instructions such as adding two numbers or moving data or jumping from one instruction to another. However, it is of course very difficult to write and debug programs in machine language. Assembly Language Programs written in a high level language such as C go through a process of translations that eventually leads to a set of instructions that can be executed by the underlying hardware. One layer of this program translation is the assembly language. A high level language is translated into assembly language. Each CPU/processor has its own assembly language. Assembly code is then translated into the target machine code. Assembly languages are human readable and contains very simple instructions. For example,
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Copyright @ 2008 Ananda Gunawardena instructions such as Add two numbers, or move memory from one place to another or jump from one place to another etc. A high level instruction written in C such as A = A + 1 could be translated into (hypothetical) Assembly as follows. Mov R1, A // move A to register 1 Inc R1 // increment R1 by 1 Mov A, R1 // move R1 to A Eventually this assembly code is mapped into the corresponding machine language so that the underlying hardware can carry out the instructions.
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