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Underclocking for reliability

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  • CPUs
  • RAM
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December 20, 2009 4:26:43 AM

Currently my FSB is running at 1333MHz.

The CPU is a Q8400 and the RAM is a PC6400 TWINX that runs at 400MHz.

From what I know, in the current scenario, the CPU is doing a lot of wait cycles on the slower RAM.

The RAM being of the "economy/value select" type, I am not going to increase it's clock.

That leaves me with underclocking the CPU to match the RAM freq.

I believe this should make my system more stable ( atleast compared to overclocking ) and have a little more life than before?

What freq. should I set the FSB at and how should I do it ( I have the GA-P45-UD3P motherboard )

What I am loking at is hardware stability and the longest possible life from my hardware

More about : underclocking reliability

December 20, 2009 5:17:52 AM

CPU bus is 333 MHz x4 and PC6400 RAM is 400 MHz x 2. There is no problem with this. If You want to match their speeds You can either overclock CPU bus to 400 MHZ x4 or underclock RAM to 333MHz x 2

I would set FSB to 400Mhz x4, RAM ratio to 1:2, this would have Your CPU running at 1600MHz bus and RAM @800Mhz. If You want You can drop CPU multiplier lower to 7 (2.8GHz) or 6 (2.4GHz).
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December 20, 2009 5:48:24 AM

KamalS said:
That leaves me with underclocking the CPU to match the RAM freq. I believe this should make my system more stable ( atleast compared to overclocking ) and have a little more life than before?
There really isn't any reason to do that. The CPU issues a memory request and waits for the "data valid" signal to come back from the memory controller. There's no harm nor anything to go wrong in this whatsoever. It's designed to work like this.
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December 20, 2009 6:52:33 AM

+1 for sminlal

Is your system actually unstable at the moment? If not, why change anything? If it is unstable, I'd suggest looking elsewhere for the problem, maybe PSU or a dodgyfied windows installation or driver. You shouldnt have to resort to running under-spec to get things working properly.
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December 20, 2009 6:54:09 AM

Ive just noticed everyone has ignored the hardware lifespan question....

Look at it this way - my 8086 Amstrad 1640 from 1984 with md-dos 1.2 still boots perfectly fine, is it any use ? not at all.
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December 20, 2009 9:43:45 AM

Don't worry about the longest possible life from our hardware. Intel gives you a 3 year warranty on a retail CPU and that's more tha enough time to get your investment out of it. In 3 years, all the apps will require greater horsepower and it forces people to upgrade. That's like saying I'm not gonna turn on the lights in my house because I want the lightbulbs to last as long as possible or I'll drive with my lights off at night and just use moonlight because I want my headlights to last as long as possible, lol.



To the guy that still has the 8086. I have no doubt it boots perfectly fine but the fine booting doesn't run Crysis or make Windows 7 snappy does it?
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December 20, 2009 10:20:52 AM

Eleven years ago, I built a P233MMX system. Later, I discovered an undocumented set of jumper settings that ran the chip at 333 MHz. I put an S370 cooler on it. Last year, I threw it out.

Stay within Intel's recommended voltage and temperature limits and short of the kind of random failures that all hardware is subject to, your system will be long obsolete before it fails.
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December 20, 2009 4:54:39 PM

I have yet to throw out any computer because it stopped working. The Radio Shack Pocket Computer I bought in 1980 still works perfectly.
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December 20, 2009 5:40:57 PM

2028764,8,450409 said:
I have yet to throw out any computer because it stopped working. The Radio Shack Pocket Computer I bought in 1980 still works perfectly.[/quotemsg

I heard there was a firmware update BIOS flash to that thing that converts it to a Blackberry!
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December 20, 2009 9:17:53 PM

With only 2K of memory I doubt it could hold more than just a few address book entries...
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December 21, 2009 12:50:15 AM

CPU FSB will need to be set at 800Mhz for a 1:1 (i think)

With modern CPU's there isnt really any advantage to underclocking.

By all means go for it if you like. Remember voltage plays an issue in component life, so remember to drop your voltages too.
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December 21, 2009 1:06:57 AM

as mrmez said under volt it then it should be very stable.
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December 21, 2009 2:09:34 AM

This is cool - I came to know about 3 new things just from this thread:

1. [ainarssems] I would set FSB to 400Mhz x4, RAM ratio to 1:2, this would have Your CPU running at 1600MHz bus and RAM @800Mhz.

2. [ainarssems] If You want You can drop CPU multiplier lower to 7 (2.8GHz) or 6 (2.4GHz).

3. [mrmez] drop voltages

I have no clue into the details of any of these, so I need to ask questions:

1. What would be the benefit of running the CPU faster than the RAM? Specifically running the CPU at twice the freq of the RAM? Would it not make the CPU wait twice the time for RAM to respond?

The reason why I want to "underclock" is to make sure the CPU does to burn idle cycles just waiting for the RAM to respond - or does it not work that way?

2. By dropping the CPU multiplier, would not the RAM and CPU be "out of sync"?

3. Are benefits of undervolting a CPU documented somewhere? I am not sure about microprocessors, but in case of microcontrollers, undervolting leads to serious electrical glitches!

These things are new to me so help me out here :-)

One thing is for sure - this sure is interesting!

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December 21, 2009 2:25:46 AM

will_chellam said:
Ive just noticed everyone has ignored the hardware lifespan question....

Look at it this way - my 8086 Amstrad 1640 from 1984 with md-dos 1.2 still boots perfectly fine, is it any use ? not at all.



Couldn't explain it better! +1 !!!
No need to underclock your CPU. Undervolt it if you want yes (assuming it works stable) but don't underclock.
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December 21, 2009 2:29:15 AM

KamalS said:
This is cool - I came to know about 3 new things just from this thread:

1. [ainarssems] I would set FSB to 400Mhz x4, RAM ratio to 1:2, this would have Your CPU running at 1600MHz bus and RAM @800Mhz.

2. [ainarssems] If You want You can drop CPU multiplier lower to 7 (2.8GHz) or 6 (2.4GHz).

3. [mrmez] drop voltages

I have no clue into the details of any of these, so I need to ask questions:

1. What would be the benefit of running the CPU faster than the RAM? Specifically running the CPU at twice the freq of the RAM? Would it not make the CPU wait twice the time for RAM to respond?

The reason why I want to "underclock" is to make sure the CPU does to burn idle cycles just waiting for the RAM to respond - or does it not work that way?

2. By dropping the CPU multiplier, would not the RAM and CPU be "out of sync"?

3. Are benefits of undervolting a CPU documented somewhere? I am not sure about microprocessors, but in case of microcontrollers, undervolting leads to serious electrical glitches!

These things are new to me so help me out here :-)

One thing is for sure - this sure is interesting!



Only got time for 3: Read my comment in the brackets above. Undervolting WITHOUT compromising the proper operation of the device. That means that some times you can't underclock at all. Sometimes a better quality process or whatever can help you underclock your CPU a little bit. Hence why use more power, excess heat etc when you can do exactly the same job with less? Help the environment we say!
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December 21, 2009 2:54:04 AM

:-)

Saving energy is my main concern.

Just next to it, is longevity.

I guess that if I sync my CPU with the RAM, then the CPU would not be burning idle cycles waiting for the RAM to respond - is this assumption of mine incorrect?

I read this thread : http://forums.anandtech.com/showthread.php?t=321110

It seems like it is possible to reduce voltages while keeping the CPU running ATLEAST at stock speed and more.

What I want to do is this:

1. Keep the RAM and CPU in sync ( I want to minimize the idle cycles of the CPU vs RAM )

2. At the same time, get the stock CPU freq although the FSB is now changed.

So maybe this is what I want to do:

1. 1333Mhz FSB == 333.25 core speed ( FSB is quad pumped )

RAM is rated at 400MHz core ( 800MHz, DDR - Dual Channel )

This means that I need to increase my FSB to 400MHz for the CPU and RAM to match?

2. So I need to set my FSB to 1600Mhz ( 400 * 4 ) for CPU and RAM speeds to match?

3. This would automagically overclock my CPU from stock 2.66 GHz = 2660Mhz to ( ( 2660 / 1333 ) * 1600 ) = 3193Mhz = 3.19GHz. Right?

4. This overclocking however would increase the power consumption as well, so I can keep temperatures down by decreasing the vcore?

Would this be a good idea?

5. Or should I reduce the multiplier ( or mutiplier settings have nothing to do with reducing power consumption? )
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December 21, 2009 3:25:18 AM

> What would be the benefit of running the CPU faster than the RAM?
The CPU will run faster when it's not waiting for stuff from the RAM. Most memory accesses are found in the CPU's cache and therefore the CPU only goes and reads stuff from RAM for perhaps 10% of the memory accesses. And the CPU does lots of other things beside memory accesses, too. So it makes absolutely no sense to slow down the CPU just because it occasionally needs to wait for RAM. It would be like lowering a freeway's speed limit to 50 km/h just because that's the speed that cars enter and leave it at.

> By dropping the CPU multiplier, would not the RAM and CPU be "out of sync"?
The CPU is hardly ever "in sync" with other components in the system anyway. The protocols between the CPU, the FSB and the other components ensure synchronization only when it's needed (ie, if I read something from RAM and it's not ready yet, I wait 'till it's ready). To use another analogy, there's no point limiting the speed of a transit bus to 5MPH just because it carries people who walk to the bus. The bus stops to pick up or drop off passengers, just like the CPU does when it can't proceed without data from another device.

> I am not sure about microprocessors, but in case of microcontrollers, undervolting leads to serious electrical glitches!
You can undervolt microcontrollers too, but not very much. The same thing applies to CPUs. We're only talking about small fractions of a volt.
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