1.5. Read and translate the text computer programming

Programming is the process of preparing a set of coded instruction which, when executed by a digital computer, yield the solution of a specific problem or perform specific functions. Each computer and each programming language has its own unique repertoire, method of operation, etc. These should be studied and understood before preparing a program on a specific language for execution by a specific computer.

A computer has the ability to automatically execute a program stored within itself. During execution of the program, the computer performs various digital operations (add­ing two numbers, moving data in and out of storage, read­ing in or printing out data, etc.). If the stored program is changed, the actions of the computer change. Thus, the com­puter actions depend on both the configuration of the com­puter hardware (the physical computer equipment) and the software (the programs stored within the computer). A given computer capability can be provided either by hard­ware alone or by a combination of hardware and software. The choice of a given mixture of hardware and software de­pends on factors such as cost, speed, ease of maintenance, and flexibility.

There are three nominal levels of programming language: machine language, assembler language, and compiler lan­guage.

Machine Language

In the machine-language programming level, the pro­grammer writes the program exactly as stored in the compu­ter. Very little programming is done at this level as it is ex­tremely tedious, and when errors are found it is hard to cor­rect them. The machine-language level is useful in the ini­tial operation of a computer when no other techniques are available, in repair of a faulty computer, and in the debugg­ing of programs when other techniques fail and the program must be examined at the machine-language level.

Assembler Language

In the assembler-language level, the programmer gener­ally writes one program instruction or one program con­stant for each memory location occupied by the program. Thus, the programmer has the same direct control over the computer operation that he would have if he wrote in machine language. However, the assembler language offers the programmer many aids such as the following.

1. The form of the assembler language is easier for hu­mans to use. For example, each instruction in assembler language is divided into a few easily understood fields; each instruction in machine language is a string of digits not easily understood. Thus, the addition of one number to another might have the form AD X3 in assembler lan­guage and 34071245 in machine language.

2. In assembler language, much of the detail of the ma­chine language can be ignored.

Compiler Language

The compiler language is an intermediate step between common human language and machine language, and is an attempt to satisfy both human and computer requirements. Thus, humans should find it easy and effective to program a computer task in compiler language, while means must be provided to automatically and quickly transform that pro­gram into machine language.

The time and effort to write a typical program in compil­er language is a small fraction of the time to write the equiv­alent program in assembler language. Programs in common­ly used compiler languages can be processed and executed in a large variety of computers, while assembler languages are usually limited to a given machine or family of machines.