4 ms·

Wasn't there some upcoming PSU spec that dropped the 5 and 3.3V rails leaving only 12V? What happened to that? Edit: Yes, the "ATX12VO" spec.

by jabl 4y ago

rocqua 4y ago
Yes, but it seems unlikely to hit consumer markets soon. It is mostly interesting for OEMs apparently. I hope I am wrong though.
- vladvasiliu 4y ago
  Aren't OEMs already able to do pretty much what they want? I have a desktop HP that has a standard-sized PSU but has a weird connector that only plugs into the motherboard. The drives are powered from a separate connector that also plugs into the motherboard. And the PSU - MB connector is much smaller than standard ATX.
  - rocqua 4y ago
    HP can control the full stack. MB and PSU at the same time. But smaller OEMs might want to not have to manufacture their own totally custom components. So it makes sense for them to standardize. If not for interchangeablity then to ensure you can sell your custom parts to other OEMs.
bombcar 4y ago
I know we don't need 5v for spinning drives anymore, but what voltage does the CPU want to see? If it's not 12V aren't we just moving the voltage drop equipment onto the motherboard?
- heretogetout 4y ago
  Consumer CPUs these days are at around 1.4 to 1.5 volts. Not sure about server, but it's probably close.
- hnuser123456 4y ago
  CPUs are around 1-1.2v. However, they can occasionally pull 100-200+W. Moving 200W at 1V means 200A. Resistive losses scale proportional to amperage at constant voltage, and inversely proportional to voltage at constant power. 200A needs a LOT of copper to not get blistering hot, the amount you would find in all the traces connecting a CPU to the VRMs on the motherboard, probably around 4 ounces just to carry the power a few inches. 200W at 12V is 16.7A, which can be shuttled much longer distances with less material at the same efficiency, in the ~foot long cable between the PSU and motherboard. Additionally, pluggable connectors are high resistance spots in the circuit unless they make very good contact, and susceptible to overheat and melt when carrying too much current.
- coder543 4y ago
  The VRMs for the CPU have already been on the motherboard for a very long time, maybe always? CPUs operate at very low voltages with very high amps. For a lot of reasons, it makes sense to keep that as close to the processor as possible.

Wasn't there some upcoming PSU spec that dropped the 5 and 3.3V rails leaving only 12V? What happened to that? Edit: Yes, the "ATX12VO" spec.

by jabl 4y ago

Wasn't there some upcoming PSU spec that dropped the 5 and 3.3V rails leaving only 12V? What happened to that? Edit: Yes, the "ATX12VO" spec.

rocqua 4y ago

Yes, but it seems unlikely to hit consumer markets soon. It is mostly interesting for OEMs apparently. I hope I am wrong though.

vladvasiliu 4y ago
Aren't OEMs already able to do pretty much what they want? I have a desktop HP that has a standard-sized PSU but has a weird connector that only plugs into the motherboard. The drives are powered from a separate connector that also plugs into the motherboard. And the PSU - MB connector is much smaller than standard ATX.
- rocqua 4y ago
  HP can control the full stack. MB and PSU at the same time. But smaller OEMs might want to not have to manufacture their own totally custom components. So it makes sense for them to standardize. If not for interchangeablity then to ensure you can sell your custom parts to other OEMs.

bombcar 4y ago

I know we don't need 5v for spinning drives anymore, but what voltage does the CPU want to see? If it's not 12V aren't we just moving the voltage drop equipment onto the motherboard?

heretogetout 4y ago
Consumer CPUs these days are at around 1.4 to 1.5 volts. Not sure about server, but it's probably close.
hnuser123456 4y ago
CPUs are around 1-1.2v. However, they can occasionally pull 100-200+W. Moving 200W at 1V means 200A. Resistive losses scale proportional to amperage at constant voltage, and inversely proportional to voltage at constant power. 200A needs a LOT of copper to not get blistering hot, the amount you would find in all the traces connecting a CPU to the VRMs on the motherboard, probably around 4 ounces just to carry the power a few inches. 200W at 12V is 16.7A, which can be shuttled much longer distances with less material at the same efficiency, in the ~foot long cable between the PSU and motherboard. Additionally, pluggable connectors are high resistance spots in the circuit unless they make very good contact, and susceptible to overheat and melt when carrying too much current.
coder543 4y ago
The VRMs for the CPU have already been on the motherboard for a very long time, maybe always? CPUs operate at very low voltages with very high amps. For a lot of reasons, it makes sense to keep that as close to the processor as possible.