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Nhấn mạnh được đặt vào phong cách rõ ràng và giải thích rằng hỗ trợ một cách tiếp cận hướng dẫn, để ngay cả những phức tạp nhất của các chủ đề được trình bày một cách sáng suốt và dễ hiểu. Cũng trong loạt bài này: Thông tin bảo mật Sổ tay John MD Hunter | 3 The Need for More Powerful Computers 3.1 Introduction Dramatic increases in computer speed have been achieved over the past 40 years but this trend will come to an end with traditional electronic technologies. The limiting factors are the speed at which information can travel and the distance it has to travel within a computer. The former is limited by the speed of light. For the latter part the technology used to reduce the size and distance between components is approaching the theoretical limit. Even if we can make the distance shorter than in the present technology another problem will arise. Simultaneous electronic signal transmission between different pairs of components will start to interfere. In other words any gains in building faster electronic components will be offset by other technical difficulties. On the other hand computer applications are becoming more complex and they demand more computer power. A few examples of current applications that need extremely powerful computers are quantum chemistry molecular modelling nanoelectronics computational astrophysics oil explorations genome sequencing and cell modelling drug discoveries modelling of human organs weather prediction and climate change modelling and financial market modelling. One way to get around this problem is to use computers having more than one processor. Such machines are commonly known as parallel computers. In the ideal case a time-consuming job can be equally divided into many sub-jobs and one processor can then handle each sub-job. These processors can thus cooperate with 18 Problems of Parallel Computers 19 each other to solve a single problem. If the sub-jobs can be executed independently then the execution time of the single job will be reduced by a factor of p where p is the number of processors in the parallel computer. Note that this is the ideal case other cases will be discussed later in this chapter. 3.2 Problems of Parallel Computers Although multiprocessor computers had
