Undervolting

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With Undervolting or sub voltes refers to the targeted lowering the supply voltage of computer processors under the manufacturer's recommended voltage. This leads to a reduced power consumption, i.e. less power consumption and less heating. It is mainly used in laptops to extend the battery life. However, it is also possible with stationary devices. Due to the lower heating, active cooling (fans) can work at a lower speed or be switched off completely without overheating. This means that the devices work more quietly or silently. ( See also: Green IT )

However, if the voltage is lowered too far, calculation errors occur, calculation programs produce incorrect results ( Prime95 is often used to test the system and detect such errors) or the system crashes / freezes. If the selected voltage is in the limit range, problems often only show up after days or weeks. For example, a MACHINE_CHECK_ EXCEPTION can be triggered, which results in a Blue Screen of Death under Windows XP .

In principle, one can say that a higher voltage is required for higher clock rates so that the transistors switch through quickly enough. If you want to lower the voltage very much, you have to reduce the clock rate (both of these are done automatically with modern processors when the load is low, but there is usually still scope for undervolting). The procedure is almost the opposite of overclocking ; there, the clock rate is increased in order to achieve more performance, which is often accompanied by an increase in voltage in order to maintain stability.

Demarcation

However, undervolting is not the exact opposite of overclocking (see: underclocking ), as you can maintain the clock rate and still reduce the voltage. In this case there is also no loss of performance. While undervolting can also result in an increase in performance with modern hardware (CPUs or GPUs can usually use the excess thermal leeway for higher average clock rates), underclocking usually results. but a lower output does not necessarily result in a lower power consumption.

Technical background of potential calculation errors when the voltage drops

In a microprocessor, for physical and manufacturing reasons, there can be no transistors that always switch from the same minimum voltage, so the normal operating voltage is determined by the manufacturer so that all transistors can always switch within a certain voltage tolerance range. However, if you reduce the voltage in a microprocessor so far that you reach or exceed the limits within which all transistors can still switch safely, then it can happen that the given voltage is no longer sufficient for some transistors and switching is no longer sufficient more or not in time.

To explain this, in simplified terms, one can imagine an 8-bit wide data line with 8 parallel lines in a processor, where each line corresponds to one bit and a transistor (T1-T8) is present at the end of the data line, which determines the value of the data stream. If a transistor is switched, then voltage is applied, which corresponds to the value 1, otherwise there is no voltage, which corresponds to the value 0. The entire data line can therefore represent an 8-bit value, for example 0000 0000, which corresponds to the value 0 in decimal notation. If, for example, all bits are to be set to the value 1 by an arithmetic operation, so that the value 1111 1111 (corresponds to 255 decimal) is present on the data line, then all transistors must switch through. If the voltage for transistors T2 and T5, for example, is too low to reliably switch these transistors, then 1111 1111 is no longer present at the end of the data line, but 1110 1101, which corresponds to the value 237 in decimal notation. So there has been a calculation error.

A voltage drop can therefore lead to the software delivering incorrect results or no longer running correctly; the hardware itself is not damaged if the voltage drops. Therefore, if the voltage drops, it must be ensured that all the transistors in the microprocessor can still switch safely. No unnecessary risk should be taken with computers in the medical, scientific or safety-relevant area, the voltage should therefore always be within the specifications.

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