or weeks needed to write the program. Assembly Language. One method programmers devised to shorten and simplify the process is called "assembly-language" programming. By assigning a short (usually three-letter) mnemonic code to each machine-language command, assembly-language programs could be written and "debugged"-cleaned of logic and data errors-in a fraction of the time needed by machine-language programmers. In assembly language, each mnemonic command and its symbolic operands equals one machine instruction. An "assembler" program translates the mnemonic "opcodes" (operation codes) and symbolic operands into binary language and executes the program. Assembly language, however, can be used only with one type of CPU chip or microprocessor. Programmers who expended much time and effort to learn how to program one computer had to learn a new programming style each time they worked on another machine. What was needed was a shorthand method by which one symbolic statement could represent a sequence of many machine-language instructions, and a way that would allow the same program to run on several types of machines. These needs led to the development of so-called high-level languages. High-Level Languages. High-level languages often use English-like words-for example, LIST, PRINT, OPEN, and so on-as commands that might stand for a sequence of tens or hundreds of machine-language instructions. The commands are entered from the keyboard or from a program in memory or in a storage device, and they are intercepted by a program that translates them into machine-language instructions. Translator programs are of two kinds: interpreters and compilers. With an interpreter, programs that "loop" back to re-execute part of their instructions reinterpret the same instruction each time it appears, so interpreted programs run much more slowly than machine-language programs. Compilers, by contrast, translate an entire program into machine language prior...
