Quiet PC
A quiet PC is a personal computer that makes very little, or no noise. Common uses for quiet PCs include video editing, sound mixing and home theater PCs, but noise reduction techniques can also be used to greatly reduce the noise from servers. There is currently no standard definition for a "quiet PC", and the term is generally not used in a business context, but by individuals and the businesses catering to them.
A proposed general definition is that the sound emitted by such PCs should not exceed 30 dBA, but 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.
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.
The first home computers, such as the Commodore 64, were very low power - and therefore could run fanless or, like the IBM PC, with a low-speed fan only used to cool the power supply, so noise was seldom an issue.
By the mid 1990s as CPU clock speeds increased above 60 MHz, "spot-cooling" was added by means of a fan over the CPU heatsink to blow air onto the processor. Over time, more fans were included to provide spot-cooling in more locations where heat dissipation was needed - including the 3D graphics cards as they grew more powerful. Computer cases increasingly needed to add fans to extract heated air from the case, but unless very carefully designed, this would add more noise.
Energy Star, in 1992, and similar programs led to the widespread adoption of sleep mode among consumer electronics, and the TCO Certification program promoted lower energy consumption. Both added features that allowed systems to only consume as much power as is needed at a particular moment - and helped reduce power consumption. In a similar manner the first low power and energy conserving CPUs were developed for use in laptops; but can be used in any machine to reduce power requirements - and hence noise.
...
Wikipedia