Molex, pentium 4

[enzo matrix]

What's with the Molex connector on some pentium 4 motherboards, both 775 and 478? I notice computers seem to work fine with and without them.

 

[icraig]

Wikipedia is you're friend....


ATX12V 1.x
While designing the Pentium 4 platform in 1999/2000, the standard 20-pin ATX power connector was deemed inadequate to supply increasing electrical load requirements. So, ATX was significantly revised into ATX12V 1.0 standard (that is why ATX12V 1.x is sometimes inaccurately called ATX-P4). ATX12V 1.x was also adopted by Athlon XP and Athlon 64 systems.

[edit] ATX12V 1.0
The main changes and additions in ATX12V 1.0 (released in February 2000) were:

An extra 4-pin, 12-volt connector to power the CPU. Formally called the +12 V Power Connector, this is commonly referred to as the P4 connector because this was first needed to support the Pentium 4 processor. (Older processors were powered from the 5V rail.)
A supplemental 6-pin AUX connector providing additional 3.3 V and 5 V supplies to the motherboard, if it needed it. Although it was provided by every ATX12V 1.x PSU (as required per standard), it was rarely required by motherboards.
Increased the power on the 12 V rail (power on 5 V and 3.3 V)

 

[enzo matrix]

^ Unfortunately, wikipedia does not seem to be my friend as not once did you mention a molex connector. These are the ones commonly connected to IDE hard drives and DVD drives with 4 pins in a single line. I am well aware of the CPU 4-pin and why it was introduced, but this is not what I am talking about.

 

[icraig]

Can't say I've ever seen what you're on about then! I've built a fair few Pentium 4 systems and a number of 775 systems and never come across one.

Have you got a picture?

 

[icraig]

Do you mean something like:

 

[enzo matrix]

Yep that's it. But they also had the regular 4-pin.

 

[Nils]

I once came across such a plug on a motherboard. In my case it could be used to power a fan or something similar. So it was a plug providing power, not requiring it.

 

[enzo matrix]

I once came across such a plug on a motherboard. In my case it could be used to power a fan or something similar. So it was a plug providing power, not requiring it.

Interesting. That makes sense.

 

[MU_Engineer]

Do you mean something like:

http://img70.imageshack.us/img70/2483/17663124kz4.jpg

Ah, that's the AM2 version of my board (abit KN8-SLI, which is a 939 board.) The Molex connector there is to provide extra power for the second PCIe x16 slot when used in SLi operation. Each PCIe x16 slot can provide up to 75 watts through the slot itself, and apparently drawing 150 W of +12V power through the main ATX connector to feed two PCIe x16 slots is a bit dicey.

 

[enzo matrix]

Ah, that's the AM2 version of my board (abit KN8-SLI, which is a 939 board.) The Molex connector there is to provide extra power for the second PCIe x16 slot when used in SLi operation. Each PCIe x16 slot can provide up to 75 watts through the slot itself, and apparently drawing 150 W of +12V power through the main ATX connector to feed two PCIe x16 slots is a bit dicey.

Nice. The 775 motherboard I've seen supported SLI. Ha, it had this chip that looks like a notebook ram chip that you flip if you want to go SLI.

 

[MU_Engineer]

Nice. The 775 motherboard I've seen supported SLI. Ha, it had this chip that looks like a notebook ram chip that you flip if you want to go SLI.

The old SLi boards that were x8+x8 rather than x16+x16 used a "Shadow Card" in the second PCIe x16 slot when it was empty to tell the chipset to route all of the PCIe lanes to the top slot. The shadow card did sort of look like the PCB of a SODIMM chip, now that you mention it. You had to have either the shadow card or a GPU in the second slot, since putting any PCIe card less than x16 in the bottom slot would cause the board not to boot. Using a PCIe x4 or x8 card on these boards is a PITA since you have to move the GPU to the bottom slot, where it buts up against the PCI slots and blocks one or both of them, depending on how large of a cooler it wears. The top slot only butts up against two PCIe x1 slots. It was a real pain to put a decent disk array in this machine since a good discrete SATA/SAS controller is an x4 or x8 card and the onboard NForce SATA controllers are bottlenecked with more than two disks due to the internal architecture of the controllers.

Modern boards don't generally need shadow cards as they can arbitrate PCIe lane switching and splitting automatically and are a big improvement over these early SLi boards. I won't miss the shadow card any once I upgrade this old machine to a proper workstation within a year

 

[enzo matrix]

Best answer selected by Enzo Matrix.