What the Power Phases row on our spec tables is counting, and when a bigger number changes anything
The VRM turns the power supply's 12V rail into the much lower voltage a processor runs on, and the Power Phases cell counts the parallel stages doing that work. The first and largest group is the one feeding the CPU. What the count does not tell you is what each stage is built from — and on the boards igor'sLAB measured, the component choice moved efficiency by more than ten percentage points while every board with a heatsink over its VRM coped with the load regardless.
A power supply hands the motherboard 12V. A CPU core runs on a small fraction of that. The voltage regulator module — the VRM — is the circuitry between the two: it steps 12V down to the voltage the processor asks for, moment to moment, and it does so under conditions that are genuinely demanding. Wikipedia's article on the buck converter, the topology this circuit is built from, puts the requirement plainly: "Modern CPU power requirements can exceed 200 W, can change very rapidly, and have very tight ripple requirements, less than 10 mV".
That is the job in one sentence: deliver a couple of hundred watts, follow a load that swings within microseconds, and keep the output flat to within hundredths of a volt. Doing it perfectly is impossible, and the part of the energy that does not reach the CPU leaves as heat. That is why the VRM sits under the largest heatsinks on the board, next to the socket, and why it is the part of a motherboard most worth understanding before you buy.
The physical components are on the board where you can see them: a row of small square packages along the top edge and down the left side of the socket, the chokes next to them, and the capacitors behind. The heatsinks bolted over that row are the subject of our cooling guide. This page is about the circuit under them and the number our spec tables print for it.
Every review on this site prints a Power Phases row, and it always holds numbers joined by plus signs — a form like 14+2+1 or 18+2. The plus signs are not arithmetic. They separate the phases into groups by what each group feeds, and the total is what you get if you add them up.
A "phase" is one parallel copy of the step-down circuit. Wikipedia describes the arrangement as one where "basic buck converter circuits are placed in parallel between the input and load", and where "Each of the n 'phases' is turned on at equally spaced intervals over the switching period". Staggering them that way buys two things: the converter "can respond to load changes as quickly as if it switched n times faster, without the increase in switching losses that would cause", and "There is also a significant decrease in switching ripple". Both of those map directly onto the requirement in the previous section.
The first number is the CPU group. It is always the largest, and it is the one being described when a manufacturer or a review says a board is "a 16-phase board". Wikipedia's figures for the scale involved — "Typical CPU power supplies found on mainstream motherboards use 3 or 4 phases, while high-end systems can have 16 or more phases" — are a useful anchor for what a big number and a small one mean.
The smaller groups after it feed other rails. Which rails, exactly, depends on the platform and on the board: the second group typically supplies the part of the processor package that is not cores, and a third, where present, supplies smaller rails again. We found no source we could read that defines this notation consistently across AMD and Intel boards or across the four manufacturers, so this page does not tell you what the second and third numbers feed on your board. Your board's own manual or specification page names them, and that is the place to look.
Of the 80 review pages on this site that carry the row, 49 print three groups and 31 print two. A cell with two numbers records the two groups the manufacturer publishes for that board. It is not a finding that the board has no third rail, and it is not a mark against it — manufacturers simply do not all break the figure down the same way. Comparing a two-number cell with a three-number one by counting the plus signs tells you about the two spec sheets, not about the two boards.
This is the part the number hides. A phase is a slot in a circuit diagram; what gets fitted into that slot is a separate decision, and it is the one that moves real behaviour.
The two broad choices are an integrated power stage — a single package containing the switching transistors and their driver, sold under names like DrMOS or Smart Power Stage — or a set of discrete MOSFETs wired up individually. igor'sLAB compared boards of both kinds on the same platform and the gap was not subtle. Of the board fitted with better parts, Igor Wallossek writes that "This can also be seen in the very high efficiency of the voltage converters, which in practice is probably only just under 95 percent in the CPU area", while "The other boards, which are all equipped with single MOSFETs, perform much worse and are only in the lower 80 percent range". The same article notes that of the boards on the bench "The Asus motherboard is the only one equipped with DrMOS", and praises its parts specifically: "The Power Stages (SiC639 from Vishay Siliconix) are not yet the upper end of the food chain, but for this price point they are very praiseworthy".
Those are igor'sLAB's figures on igor'sLAB's boards, on a platform that is now several generations old. Read them as the size of the effect, not as numbers that apply to any board you are looking at. The point that carries across is the ordering: what a phase is made of decided efficiency there, and the count did not.
The integrated parts also change what the board can tell you about itself. The same article observes that "Current Smart Power Stages (SPS) offer this return value as IMON even in very small intervals and very exactly", but that "for cost reasons, none of the boards has the necessary combination of SPS and suitable PWM controller built in, so that all four motherboards have to rely on the so-called Inductor DCR" — a less exact way of estimating current, and one reason the power figures software reports for a CPU differ from board to board.
An advertised phase count is sometimes described as being reached with phase doublers, so that a printed number is not the same as the number of independently controlled circuits. We could not read a source that documents this, so this page makes no claim about doublers and no claim that any particular count is or is not "real". If that distinction matters to your decision, the thing to look for is the board's PWM controller part number and its channel count, which neither our spec tables nor most manufacturer pages publish.
For a stock, non-overclocked CPU on a mid-range board, the phase count is not the thing that limits you. Set the two figures side by side: Wikipedia's description of the field has "Typical CPU power supplies found on mainstream motherboards use 3 or 4 phases" with 16 or more at the high end. The first number on our own review tables runs from 4 to 24, and only ten of the 80 boards sit below ten — so a current board of almost any price is already past the mainstream figure in that description, and most are near or beyond the high-end one. That is why a phase count is a poor way to tell two current boards apart.
What separates them is what those phases are made of, covered above, and whether the heat gets away from them. On the boards igor'sLAB put under load, "All boards with VRM coolers had no problems with higher loads, even if the voltage regulator losses were higher with one or the other board" — the losses differed, the outcome under load did not, because the heatsinks carried the difference away. So the questions worth asking about a board's power delivery, in order, are: is there a real finned heatsink over the VRM rather than a flat cover, will the case move air across the top of the board, and only then how the phase count compares. Our cooling and thermals guide covers the first two, including what to look for in a VRM heatsink and airflow planning.
The count starts to matter when you are pushing a high-core-count processor past its stock power limits for sustained periods, because that is the case where the losses in the previous paragraph stop being a rounding error. If that is not you — and for most builds it is not — a board chosen for its chipset, its M.2 layout and its form factor will not disappoint you because of this row.
The Power Phases row sits in the spec table near the top of every review, and every review also carries a VRM & Power Delivery section further down that describes the board's power delivery in prose. Both are on all 80 review pages on this site.
Use the row the way this page has described it: read the first number as the CPU group, treat the rest as a breakdown the manufacturer chose rather than a score, and do not rank two boards by adding the numbers up. Then look past it at the section below the table and at the board's photograph, where the heatsink over that circuit is visible.
The full set is in our reviews index, and the compare tool puts the Power Phases rows of two boards side by side. If you want the count for a specific board, that cell is the place it lives — deliberately, this page states none of them.
The circuit description, the multiphase behaviour and the mainstream-versus-high-end phase figures on this page come from Wikipedia's buck converter article; the efficiency figures, the DrMOS and single-MOSFET comparison and the current-sensing point come from igor'sLAB, and are that publication's measurements on that publication's boards, not ours. We have no test bench and no hardware here: nothing on this page is a measurement of ours, and no board on this site has had its VRM inspected or its temperature recorded by us. The counts of 80 review pages, 49 three-group cells and 31 two-group cells, and the 4-to-24 range of the first number, were taken from the spec tables of this site's own review pages on 9 September 2026. We found no readable source for phase doublers or for a cross-vendor legend to the second and third numbers, so this page states neither.
Published 9 September 2026. Spec-row counts taken from our own review pages on 9 September 2026.