[SOLVED] What does O.C. Mean for Mobo Memory?

Feb 15, 2021
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Okay, so I know O.C. means overclock, but hear me out. My understanding is that any RAM speed above 2133 or 2400 MHz is considered an overclock for the RAM. However, on some Mobo specs, you'll se something like:

DDR4 5100(O.C)/5000(O.C)/4800(O.C.)/4600(O.C)/4400(O.C)/4266(O.C.)/4133(O.C.)/4000(O.C.)/3800(O.C.)/3600(O.C.)/3466(O.C.)/3400(O.C.)/3200/3000/2933/2800/2666/2400/2133 MHz

Where 3200/3000/2933/2800/2666 MHz speeds are not listed as overclocks. Why is this? I believe this is saying "Speeds above 3200 MHz go above the memory controller for typical compatible CPUs", but I'm not sure that's correct. If that is true, would the memory controller be overclocked if the RAM is set to speeds over 3200 MHz?
 
The O.C. in parenthesis means the motherboard "can" support that memory speed but it's an overclock since it's not on-spec for the memory controller and/or DDR4 memory standard.

The "can" is in parenthesis since it is an overclock so no guarantees and you'll be hard pressed to determine which of the three (memory, memory controller, motherboard) is the reason it doesn't work, if it doesn't work.
 
The O.C. in parenthesis means the motherboard "can" support that memory speed but it's an overclock since it's not on-spec for the memory controller and/or DDR4 memory standard.

The "can" is in parenthesis since it is an overclock so no guarantees and you'll be hard pressed to determine which of the three (memory, memory controller, motherboard) is the reason it doesn't work, if it doesn't work.
 
Feb 15, 2021
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It means that the non OC speeds are supported natively by the chipset, whereas the OC speeds requires XMP activation which is a sort of auto OC pre programmed into the memory controller.
Correct me if I'm wrong, but I thought RAM would run at 2133/2400Mhz if XMP wasn't enabled. Are you saying, for example, that 3200Mhz RAM would have that speed out of the box if the chipset supported it?
 
Correct me if I'm wrong, but I thought RAM would run at 2133/2400Mhz if XMP wasn't enabled. Are you saying, for example, that 3200Mhz RAM would have that speed out of the box if the chipset supported it?
I think it depends a lot on how the BIOS initializes memory in conjunction with the default (non-XMP) memory timings on the DIMM's. Reason being: I have one GSkill RAM kit that always starts up in 2666, it's rated speed, in two motherboards. But in a third it initializes at 2133. My GSkill 3200 kit initializes in two boards at 2133...one at 2400 and that has changed with my B550 board since the first BIOS revision. So whatever rationale it's using, there's too many variables at play to develop any hard and fast rules with just that to go on.

When I say 'starts up', I mean initial start up after a CMOS reset when the memory controller first trains memory.
 

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