Programming

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Programming A program is a sequence of instructions that tells the hardware of a computer what operations to perform on data. Programs can be built into the hardware itself, or they may exist independently in a form known as software. In some specialized, or "dedicated," computers the operating instructions are embedded in their circuitry; common examples are the microcomputers found in calculators, wristwatches, automobile engines, and microwave ovens. A general-pur pose computer, on the other hand, contains some built-in programs (in ROM) or instructions (in the processor chip), but it depends on external programs to perform useful tasks. Once a computer has been programmed, it can do only as much or as little as the software controlling it at any given moment enables it to do. Software in widespread use includes a wide range of applications programs-instructions to the computer on how to perform various tasks. Languages. A computer must be given instructions in a "language" that it understands-that is, a particular pattern of binary digital information. On the earliest computers, programming was a difficult, laborious task, because vacuum-tube ON-OFF switches had to be set by hand. Teams of programmers often took days to program simple tasks such as sorting a list of names. Since that time a number of computer languages have been devised, some with particular kinds of functioning in mind and others aimed more at ease of use-the "user-friendly" approach. Machine Language. Unfortunately, the computer's own binary-based language, or machine language, is difficult for humans to use. The programmer must input every command and all data in binary form, and a basic operation such as comparing the contents of a register to the data in a memory-chip location might look like this: 11001010 00010111 11110101 00101011. Machine-language programming is such a tedious, time consuming, task that the time saved in running the program rarely justifies the days 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.

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