TAILIEUCHUNG - HandBooks Professional Java-C-Scrip-SQL part 124

Tham khảo tài liệu 'handbooks professional java-c-scrip-sql part 124', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | programs and system programs as they attempted to add more and more features to those available in the previous This illustrates what I call the Iron Law of Programming whenever more resources are made available a more ambitious project is attempted. This means that optimal use of these resources is important no matter how fast or capacious the machine. Why Optimization Is Often Neglected In view of this situation why has optimization of application programs not gained more attention I suspect that a major reason is the tremendous and continuing change in the relative costs of programming time and computer hardware. To illustrate this let us examine two situations where the same efficiency improvement is gained but the second example occurs after twenty years of technological improvement. In the early 1970 s a programmer s starting salary was about 3 per hour and an hour of timesharing connect time cost about 15. Therefore if a program originally took one hour to run every day and the programmer spent a week to reduce this time by 20 in about eight weeks the increased speed would have paid for the programmer s time. In the late 1990 s the starting salary is in the vicinity of 15 per hour and if we assume that the desktop computer costs 2500 and is amortized over three years the weekly cost of running the unoptimized program is about . Holding the other assumptions constant the optimization payback time is about 30 years 6 This long-term trend seems to favor hardware solutions for performance problems over the investment of programming effort. However the appropriate strategy for performance improvement of a program depends on how much control you have over the hardware on which the program will run. The less control you have over the hardware the greater the advantage of software solutions to performance problems as illustrated by the situations below. Considering a Hardware Solution While every optimization problem is different here are some general

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