Dale - Computer Science Illuminated 48

Dale - Computer Science Illuminated 48 - structured...

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1.2 The History of Computing 21 Assembly languages Systems software High-level languages Machine language Application packages Figure 1.9 The layers of software surrounding the hardware continue to grow The separation between the user and the hardware was growing wider. The hardware had become only a small part of the picture. A computer system—a combination of hardware, software, and the data managed by them—had emerged. See Figure 1.9. Although the layers of languages kept getting deeper, programmers continued (and still continue) to use some of the very inner layers. If a small segment of code must run as quickly as possible and take up as few memory locations as possible, it may still be programmed in an assembly language or even machine code today. Fourth Generation (1971–1989) The 1970s saw the introduction of better programming techniques called
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Unformatted text preview: structured programming , a logical, disciplined approach to programming. The languages Pascal and Modula-2 were built on the principles of struc-tured programming. And BASIC, a language introduced for third-genera-tion machines, was refined and upgraded to more-structured versions. C, a language that allows the user to intersperse assembly-language statements, was also introduced. C++, a structured language that also allows the user access to low-level statements, became the language of choice in industry. Better and more powerful operating systems also were being developed. UNIX, developed at AT&T as a research tool, has become standard in many university settings. PC-DOS, developed for IBM PC, and MS-DOS, developed for compatibles, became standards for personal computers. The...
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