How to Underclock a GA-890GPA-UD3H / 1090T?

[dframeli]

I have a GA-890GPA-UD3H and 1090T mounted iin a HTPC.

I'm interested in creating 2 very different sets of BIOS settings...  a low temperature / low voltage BIOS profile that will keep my HTPC running cool and quiet, and a over-clocked profile for gaming.

I've never underclocked a MB/CPU before... Which BIOS settings do I change, and how low is it low can I set the CPU's speed and voltage - while keeping the system completely stable?     

 

[Dark Mantis]

Once again it is the same as when you overclock, you have to try a setting and see if it is stable, if so then move on a bit further. In the same way you will reach a point where your system will not run happliy and you will have to increase the settings slightly.
Absic can probably give you some more specific help as he knows these boards a lot better than me.

[absic]

Hi there and welcome to the forum.

I have the1090T and have been able to O/C to 4.2 GHz without too many issues. Under-clocking the CPU has presented a few different challenges but can also be quite successful if you take your time. I don't have the same Mobo as you but the principals should be the same. ( I have the GA-790XTA-UD4)

When under-clocking the CPU I have found the first thing to do is disable the Turbo Core option in BIOS (if your BIOS allows you to do this). This will keep the cores of the processor running at a constant speed. Another thing to do will be to reduce the overall speed of the CPU from it's 3.2 GHz. To do this you need to adjust the CPU Clock Ratio. The third area is the CPU Voltage this can be reduced under the CPU Voltage Control in BIOS. This allows the reduction to be made in steps of .025V. As an indication of what can be achieved, on my board, leaving the CPU at stock speed I can reduce the voltage by .050V before it starts becoming a bit temperamental. Remember to keep an eye on your RAM as you might find you need to make adjustments here as well to improve stability.

If you really want to reduce the overall power draw, another option is to disable some of the cores. You can effectively turn your Hex Core into a Dual Core which will obviously have a major impact but, if all you want to do in this state is watch movies then a Dual Core will do the job just as well.

As Dark Mantis has already stated, under-clocking is as much an art as is Over-clocking and it can be just as difficult obtaining a stable system. You may find that your system will fall over and then fail to BOOT. If this does happen, don't panic. Take your time to clear CMOS properly and the system should then start. Re-load Optimized Defaults and start tweaking again.

[dframeli]

Guys,
 
  Thanks for the insight.

  Any ball park estimates as to what sort of under clocked CPU speeds can I expect?

  For now, I'd like to keep all 6 cores online, but the CPU speed I'd like to get down to around 2.2GHz or so (if possible)

  Can you offer a good starting point with regards to an appropriate CPU Clock Ratio and CPU voltage? 

Thanks again!
Dale

[absic]

Hi Dale,

just tried a little bit of playing around with my own system in an effort to get an answer for you and what do you know, it was pretty easy to get down to 2.2 GHz. Just set the CPU Clock Ratio to X11, disable the Turbo Core Boost option (not sure if your mobo BIOS has this) and then leave everything else on AUTO. Rebooted and had one much slower but fully functioning PC. Now how hard is that? Once you have checked out , how the system runs with the CPU set at 2.2 GHz then you can start to play with reducing the voltage on the CPU.

Pulling back the CPU Voltage is going to be a little harder and, as each CPU/Board/RAM combination works differently it really is going to need a hands on approach. As I mentioned earlier, I have been able to run my CPU at stock speed 3.2 GHz and been able to reduce the voltage by .050V. If I go lower than that it becomes a little glitchy. Obviously, with the under-clock you are hoping to achieve, you should be able to reduce the voltage a bit further but I guess this initial .050V reduction is a good place to start.

[dframeli]

Haven't reduced the voltage yet, but dropping down to 2.2GHz simply by changing the multiplier was, as you said, very easy

I'll keep my eyes and ears open to see my HTPC runs any cooler or any more quiet. 

If I don't mess with the CPU voltage, will the MB adjust automatically to the reduced CPU speed?  Or do I need to manually set it?

Thanks!

[dframeli]

My "Normal CPU Vcore" read 1.375V.  I dropped it down to 1.3250V and will continue to test.

[Dark Mantis]

It would seem like you are getting there slowly with absics's help. Another thing that you may not be aware of is that most fans will run on 7v minimum so you can slow them down by undervolting also which again makes less noise.

[absic]

If I don't mess with the CPU voltage, will the MB adjust automatically to the reduced CPU speed?  Or do I need to manually set it?

If you leave things set at AUTO the voltages will be reduced/increased as the load demands which is why I suggested leaving them at auto at first. The voltage figures you can see in BIOS are the ones that the motherboard wants to run with and are a good starting point for making further reductions.

On my 790XTA Mobo, with the 1090 at stock the CPU VCore is 1.4750 so you are already under this.