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12 Volt rails - what is that and what makes it so special?

When speaking about power supply units you often hear of "12V rails", which are sometimes merged and sometimes are not. But what does that mean exactly? What are these mysterious rails? And what makes them important?

Back in the day chip components like CPU, GPU or logic circuits used a core voltage of 5V while other components such as fans, drive motors, sound cards or serial interfaces demanded 12V. Over the years the clock rate of those chips continually increased while at the same time the core voltage of the CPU sank to 3.3V.  Which means that the PSU had to provide several different voltages in order to be able to meet the demands of the different components directly and precisely: 3.3V, 5V and 12V (additionally there were also -5V and -12V but that's a different topic).

So while the internal structure of the CPUs grew increasingly smaller and the clock rates at the same time higher, the core voltage shrunk and became ultimately variable. Additionally motherboards and graphics cards used their own integrated voltage regulators which siphoned the energy they needed from the available 12V the ATX PSU provided. Which means that over the years the 12V rail became the most important energy delivery line for ALL voltages. PSUs with DC/DC technology even create their 5V and 3.3V internally from the 12V. These other rails are therefore known as "minor rails".

Multi rail PSUs feature a dedicated OCP on each rail. This stands for "over current protection" and regulates the maximum power on each rail. This is a very useful function as it protects the connected components from short-circuits or overloads and prevents cable fires. Using the "single rail" mode deactivates these regulations which of course slightly increases the risks of cables and components - but at the same time offers the full power and an even workload on each rail which is especially important for overclocking.

Some of our power supply units (such as the "Dark Power Pro 11" feature an "overclocking key" which does exactly that: It merges the available rails to ONE massive 12V rail.



So, does that mean that the more 12V rails are available, the better? Well, yes and no. If you need a higher performance or intend to do some major overclocking, one big 12V rail makes a lot of sense. On the other hand, if you use your PC for working, the occasional gaming or video and graphics editing you will probably never need this additional boost. But it's good to have it up your sleeve, in case you might need it.