Intel’s ATX12VO Standard: A Study to Increase Computer Power Efficiency

The venerable ATX standard was developed in 1995 by Intel, with the goal of standardizing what had until then been a PC ecosystem formed around IBM’s AT PC heritage. The previous AT form factor was not so much a standard as the rough copy of the IBM AT motherboard and with it all its flaws.

With the ATX standard also came the ATX power supply (PSU), the standard of which defines the standard voltage rails and the function of each additional feature, such as soft power-on (PS_ON). As with all electrical appliances and gadgets of the 1990s and beyond, ATX power supplies were subject to energy efficiency regulations, which also led to the 80+ certification program in 2004.

Since 2019, Intel has been promoting the ATX12VO (12V only) standard for new systems, but what is this new standard all about, and will switching everything to 12V really be worth saving energy? ?

What is ATX12VO

As the name suggests, the ATX12VO standard basically does away with the other voltage rails that currently exist in the ATX PSU standard. The idea is that by providing a single base voltage, all other voltages can be generated as needed using buck (buck) converters. Since the Pentium 4 era, this has already become standard practice for the CPU and much of the motherboard circuitry anyway.

As the ATX PSU standard moved from older 1.x revisions to the current 2.x revision range, the -5V rail was removed and the -12V rail became optional. The ATX power connector with the motherboard was changed from 20 to 24 pins to allow for the addition of more 12V capability. Along with the Pentium 4’s appetite for power came the new 4-pin motherboard connector. pins, which is commonly referred to as the “P4 connector”, but officially the “+12V Power 4 Pin connector” in the v2.53 standard. This adds two more 12V lines.

Power input and output on the ASRock Z490 Phantom Gaming 4SR, an ATX12VO motherboard. (Credit: Anandtech)

In the ATX12VO standard, the -12 V, 5 V, 5 VSB (sleep) and 3.3 V rails are removed. The 24 pin connector is replaced by a 10 pin connector which carries three 12 V lines (one more than ATX v2.x) in addition to the new 12 VSB standby voltage rail. The 4-pin 12V connectors would still remain, and one or two would still have to be squeezed through incredibly small gaps in the system case to get them to the top of the motherboard, near the voltage regulation modules (VRMs) of the processor.

While the PSU itself would be somewhat streamlined, the motherboard would gain those VRM sections for the 5V and 3.3V rails, as well as power outputs for SATA, Molex, and the like. Essentially, the motherboard would take over some of the PSU functions.

Why ATX12VO exists

A range of Dell computers and servers that will be subject to strict California efficiency regulations.

The folks at GamersNexus covered their research and industry thoughts on the ATX12VO topic in an article and video published last year. In short, OEM system builders and system integrators are subject to fairly strict energy efficiency regulations, especially in California. From July 2021, new Tier 2 regulations will come into effect that will add more stringent requirements for OEM and IS computing equipment: see 1605.3(v)(5) (especially Table V-7) for details .

To meet these ever-increasing efficiency demands, OEMs have created their own proprietary 12V-only solutions, as detailed in GamersNexus’ recent video review of the Dell G5 5000 pre-built desktop system. The ATX12VO d ‘Intel would therefore seem more focused on unifying these proprietary standards than on replacing ATX v2.x power supplies in DIY systems. For the latter group, which builds its own systems from standard ATX, mini-ITX and similar components, these strict efficiency regulations do not apply.

So the main question is whether ATX12VO makes sense for DIY system builders. While the ability to (theoretically) increase power efficiency, especially at low loads, sounds beneficial, it’s not impossible to accomplish the same with ATX v2.x PSUs. As an unnamed PSU manufacturer stated in the GamersNexus article, ISs will likely end up just using high-efficiency ATX v2.x PSUs to meet California Tier 2 regulations.

Evolution vs Revolution

Seasonic CONNECT DC-DC module connected to a 12V power supply. (Credit: seasonal)

Since the original ATX PSU standard, the improvements have been incremental and never disruptive. Although some were taken aback by the negative voltage rails being left out when trying to power older motherboards that relied on -5V and -12V rails, in general these changes were enough. miners to incorporate them into the computer’s natural upgrade cycle. systems. This is not the case with ATX12VO, as it absolutely requires an ATX12VO PSU and motherboard to achieve the increased efficiency goals.

Although it is possible to use an ATX v2.x to ATX12VO adapter which passively adapts the 12V rails to the new 10-pin connector and increases the 5 VSB line to 12 VSB levels, this actually reduces efficiency instead to increase it. Essentially, the only way ATX12VO will make much sense is if the industry switches immediately and everyone upgrades as well without reusing non-ATX12VO compatible motherboards and PSUs.

Another crucial point here is that OEMs and IS are not required to adopt ATX12VO. Much like Intel’s ill-fated BTX alternative to the ATX standard, ATX12VO is a suggested standard that manufacturers and OEMs are free to adopt or ignore as they see fit.

The obvious negatives introduced by ATX12VO are probably important here:

  • Adding another hotspot to the motherboard and taking up valuable board space.
  • Turning motherboard makers into power supply makers.
  • Increased cost and complexity of motherboards.
  • Peripheral power routing (including case fans) from the motherboard.
  • Make it harder to troubleshoot power issues.
Internal components of Seasonic’s CONNECT modular power supply. (Credit: Tom Material)

Add to that potential alternatives like Seasonic’s CONNECT module. This effectively does the same thing as the ATX12VO standard, removing the 5V and 3.3V rails from the PSU and moving them to an external module, off the motherboard. It can be installed in the area behind the motherboard in many computer cases, allowing very clean cable management. It also allows for increased efficiency.

Since PSUs tend to survive at least a few system upgrades, one could argue that from an environmental perspective, it is undesirable to have the minor rails generated on the motherboard. Perhaps the least desirable aspect of the ATX12VO is that it reduces the modular nature of ATX-like computers, making them look more like laptop-like systems. Instead, a more reasonable solution here might be a CONNECT-like solution that offers both a 24-pin ATX and 10-pin ATX12VO connectivity option.

think bigger

In the larger picture of energy efficiency, it can be beneficial to step back from details such as the innards of a computer system and examine, for example, the alternating current (AC) of the mains that powers these systems. A well-known property of switch-mode power supplies (SMPS) like those used in any modern computer is that they are more efficient at higher AC input voltages.

Power supply efficiency at different input voltages. (Credit: HP)

This is clearly seen when looking at, for example, the rating levels for the 80 Plus certification. Between 120 VAC and 230 VAC line voltage, the latter is significantly more efficient. To this can also be added the resistive losses due to carrying double the amps on the house wiring for the same power draw at 120 V versus 230 VAC. That’s why data centers in North America typically run on 208 VAC according to this APC white paper.

For crypto miners and the like, wiring their computer room for 240 VAC (North American hot-neutral-hot) is also a popular topic, as it directly increases their profits.

Future prospects

It’s hard to say whether ATX12VO will become the next big thing or die out like BTX and so many other proposed standards. One thing the ATX12VO standard certainly has against it is that it requires many large changes in parallel, and the creation of a lot of electronic waste by forced upgrades in a short period of time. Considering that many ATX and SFX type PSUs come with 7-10 year warranties compared to the much shorter lifespan of motherboards, this poses a significant hurdle.

Based on the sounds of the industry, it seems very likely that a lot of things will remain “business as usual”. There are plenty of efficient ATX v2.x power supplies out there, including those rated 80 Plus Platinum and Titanium, and Seasonic’s CONNECT and similar solutions would strongly appeal to those who like neat cable management. For those who buy pre-built systems, the use of ATX12VO is also irrelevant, as long as the hardware complies with all (efficiency) regulations. The ATX v2.x standard and 80 Plus certification also changes to set strict charging efficiency targets of 2-10%, which is the primary target with ATX12VO.

How would you benefit from switching to ATX12VO, and would you choose it over a solution like Seasonic CONNECT if both offered the same levels of efficiency?

(Header image: Asrock Z490 Phantom Gaming 4SR with SATA power connected, credit: c’t)

Alan A. Seibert