外文翻譯---軟件和軟件工程(文件)
【正文】 ation was often nonexistent. During the early years we learned much about the implementation of puterbased systems, but relatively little about puter system engineering .In fairness , however , we must acknowledge the many outstanding puterbased systems that were developed during this era. Some of these remain in use today and provide landmark achievements that continue to justify admiration. The second era of puter system evolution (Figure ) spanned the decade from the mid1960s to the late 1970s. Multiprogramming and multiuser systems introduced new concepts of humanmachine interaction. Interactive techniques opened a new world of applications and new levels of hardware and software sophistication. Realtime systems could collect, analyze, and transform data form multiple sources, thereby controlling processes and producing output in milliseconds rather than minutes. Advances in online storage led to the first generation of database management systems. The second era was also characterized by the use of product software and the advent of software houses. Software was developed for widespread distribution in a multidisciplinary market. Programs for mainframes and miniputers were distributed to hundreds and sometimes thousands of users. Entrepreneurs from industry, government, and academia broke away to develop the ultimate software package and earn a bundle of money. As the number of puterbased systems grew, libraries of puter software began to expand. Inhouse development projects produced tens of thousands of program source statements. Software products purchased from the outside added hundreds of thousands of new statements. A dark cloud appeared on the horizon. All of these programsall of these source state mentshad to be corrected when faults were detected, modified as user requirements changed, or adapted to new hardware that was purchased. These activities were collectively called software maintenance. Effort spent on software maintenance began to absorb resources at an alarming rate. Worse yet, the personalized nature of many programs made them virtu ally unmaintainable. A software crisis loomed on the horizon. The third era of puter system evolution began in the mid1970s and continues today. The distributed systemmultiple puters, each performing functions concurrently and municating with one another
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