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A quiet PC is a personal computer that makes little noise. Common uses for quiet PCs include video editing, sound mixing, home servers, and home theater PCs. A typical quiet PC uses quiet cooling, quiet storage devices, and energy-efficient parts. Like noise, the term "quiet PC" is subjective and there is currently no standard definition for a "quiet PC". A proposed general definition is that the sound emitted by such PCs should not exceed 30 dBA. In addition to the average sound pressure level, the frequency spectrum and dynamics of the sound are important in determining if the sound of the computer is noticed. Sounds with a smooth frequency spectrum (lacking audible tonal peaks), and little temporal variation are less likely to be noticed. The character and amount of other noise in the environment also affects how much sound will be noticed or masked, so a computer may be quiet with relation to a particular environment or set of users.〔 ==History== Prior to about 1975, all computers were typically large industrial/commercial machines, often in a centralized location with a dedicated room-sized cooling system. For these systems noise was not an important issue. With the development of the home computer, early systems such as the Commodore 64 were very low wattage and were often fanless. If there was a fan, it was a low-speed fan only used to cool the power supply, such as in the IBM PC XT. Fan noise only started to become an issue as CPU processing power increased. Processors up to about 60 megahertz did not require anything more than a single case fan and a passive heatsink. Beyond that point, a fan would be installed over the CPU heatsink to blow air straight down onto the processor, in what is known as ''spot-cooling''. There was no regard for where the intake air came from, or where exhaust was going. The sole purpose of the fan was to move heat from a small concentrated location under the heatsink into the larger air mass inside the computer case. As desktop computers grew in performance, more fans were included to provide spot-cooling in many more specific locations where heat dissipation was needed, without regard to overall airflow or trying to do thermal analysis of cooling efficiency. * Originally, video display controllers were fairly low power devices without any need for active cooling. But with the development of the 3D graphics card, it became common for the video card to have its own fan, separate from a general case/system fan. The development of 3D cards working in tandem required separate spot-cooling fans for each card. * Multiprocessor systems such as the Pentium Pro typically needed a separate spot-cooling fan for each CPU. Computer cases often have not been designed to consider the overall airflow of the system, while spot-cooling fans only focus on cooling a specific location without regard to where the exhaust air is going. Sometimes fan airflow is not coordinated, such as with the power supply and case fans both blowing air in or sucking air out, with no other venting. This combination could lead to a system with a large number of internal spot-cooling fans that is overheating because there is poor overall airflow into and out of the case. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Quiet PC」の詳細全文を読む スポンサード リンク
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