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What does vccsa and vccio actually do?

masterding
Level 7
I know this question has been ask many time before. but it seems there're different answers to this same old question.
popular opinion is that VCCSA is System Agent Voltage, and it stabilizes or helps overclock BLCK, while VCCIO (commomly known as VTT/QpI) is IMC Voltage and helps stabilize when overclocking RAM .
VCCIO: more commonly known at QPI/VTT voltage, this is the VTT voltage. Formally known as Processor Power for I/O it is the voltage for the integrated memory controller as well as the PCI-E controller.

But an article from hardwaresecrets has exactly the opposite opinion, it says
VTT: This is the rail that feeds the integrated memory controller (on CPUs that have this component), the QPI bus (on CPUs that have this component), the FSB termination (on CPUs that are based on this architecture), the L3 memory cache (on CPUs that have this feature), the thermal control bus (PECI, Platform Environmental Control Interface, on CPUs that have this feature, except from second-generation Core i processors on, where this bus is fed by the VCCIO voltage) and other circuits, depending on the CPU. It is important to understand that on AMD CPUs, “VTT” is the name of a different voltage; the VTT on Intel CPUs is the equivalent of the VDDNB from AMD CPUs. This voltage can be changed through options such as “CPU VTT,” “CPU FSB,” “IMC Voltage,” and “QPI/VTT Voltage.”
•VCCSA: Starting with the second-generation Core i processors (“Sandy Bridge”), the VTT voltage was renamed to VCCSA, and is called “system agent.” It feeds the integrated PCI Express controller, memory controller, and display engine (i.e., the “2D” part of the graphics engine).
•VCCIO: Available starting with the second-generation Core i CPUs (“Sandy Bridge”), this voltage is used for feeding all input/output (I/O) pins of the CPU, except memory-related pins. On CPUs that have this voltage, it is also used to feed the thermal control bus (PECI, Platform Environmental Control Interface).

From the article we can see, VTT was renamed to VCCSA not VCCIO ,and it feeds voltage to the IMC, while VCCIO is voltage for (I/O) pins of the CPU, except memory-related pins, in their opinion it seems VCCIO has nothing to do with IMC.
so which one really powers IMC, VCCSA or VCCIO? My sense is that since VCCSA is system agent voltage and IMC is part of system agent, it's logical to say VCCSA powers IMC, then what does VCCIO do? now VCCIO is split into VCCIO-A and VCCIO-D, what's difference between them then, how do they function differently?
thanks.
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6 REPLIES 6

Nate152
Moderator

RickSinGA
Level 11
Cut and Paste, oopsy?

RickSinGA wrote:
Cut and Paste, oopsy?

What do you mean ,sir?

masterding
Level 7
I don't have any issue with any of my credit card , besides I'm in China ,so I don't think your information will be of any help to me , thank you for sharing anyway.:D

Nate152
Moderator
The system agent voltage is the vccsa. You increase this voltage if you are unstable running high speed ram.

Nate152 wrote:
The system agent voltage is the vccsa. You increase this voltage if you are unstable running high speed ram.

I agree , we can come to the conclusion from the name, SA I asssume repesent system agent ,but this is not what I want to know.