Please Advise. Pushing Lower CAS Latency

[idolwalrus]

Building my first computer. I've read up a lot on forums, but as you learn more... the questions get more specific.

I'm wanting to know, based on what is said in this post http://www.tomshardware.com/forum/223944-30-please-advise-latency-confusion if I can underclock:

Capacity 4GB (2 x 2GB)
Speed DDR2 1066 (PC2 8500)
Cas Lat 5
Timing 5-5-5-15
Voltage 2.0V - 2.1V

to a speed of 667 and Cas Lat. of 3.



I'm doing this because (and correct me if I'm wrong) I'd rather underclock my RAM to match my motherboard (GA-P35-S3G LGA 775 Intel P35 ATX Intel Motherboard) and processor (Core 2 Duo e8400) than overclock the others. My reason is to prevent the need for any extra cooling (my case http://www.newegg.com/Product/Product.aspx?Item=N82E16811156062 )

So first, I'd like to know if I can underclock my RAM like that and what that would entail.
Second, am I on the right track to get the best from those parts?

 

[outlw6669]

Yes you can.
All it takes is changing a few simple settings in your BIOS.

First off, let me make a suggestion.
Up your FSB to 400Mhz and either leave your CPU at 3.6Ghz or drop your multiplier to 8x for a 3.2Ghz overclock. This will give you two benefits. First, an overclocked CPU will give you a much larger performance increase than optimised RAM speed/timings. Second, your RAM should be able to get good timings at 400Mhz, or DDR2 800 speeds, and give you even better performance.

What ever you do with the CPU, optimising your RAM timings is fairly straight forward. In your BIOS, set your RAM speed to a 1:1 ratio or the lowest speed setting available. Change your RAM voltage to the maximum specified by the manufacturer. Make sure to have your copy of Memtest86+ ready for the following steps.

Change your ram timings from Auto to Manual one at a time starting with the top setting, CL or CAS Latency. Start with this setting at 3 for DDR2 666 or 4 for DDR2 800 speeds. Save and exit. Allow Memtest86+ to load and start testing. I would recommend innately testing for a minimum of 10min to see if there are any errors. If there are none, lower the CL setting by one and retest. As soon as you start getting errors, raise it one notch and move down to the next setting.

The next three settings are the second most most important after the CL setting. These would be tRCD or RAS to CAS Delay, tRP or RAS Precharge and tRAS or Active to Precharge Delay. If you have a CMD or Command Rate setting, this is also an important one. Depending on your BIOS, you may be able to change about 20 more settings but none are as important as the afore mentioned settings.

The methodology is the same for all settings. Start with a higher setting and slowly test your way to instability. When you have all settings to their lowest stable with a short stint of Memtest, let it run overnight or all day while you are at work. This will give you final validation that everything will stay stable during heavy use.

I am optimising 4x 1Gb sticks of Mushkin PC8500 rated at 5-5-4-12, 2.35V on a P45 Mb which has every timing setting available to be changed. So far, with at 1:1 with a 400Mhz FSB and 2.3V I have it stable at 4-3-3-3-1-20-3-1 2-7-auto for the rest of the settings. Not sure if I feel any difference but it is pretty cool to be able and say that absolutely everything in your system has been optimised.

 

[asdasd123123]

That CPU has a FSB of 1333Mhz, and that motherboard supports 1333Mhz fsb, and 1066 on ram.

I don't see the point in running half the clock speed on DDR2.
Those lower latencies will definitely not make up for the loss of 4gb/s bandwidth.

You won't even be overclocking anything.

 

[outlw6669]

Really?

C3 DDR2 667 has a full 1ns lead in access time over C4 DDR2 800 and C5 DDR2 1000. Also, these calculations only account for CAS timings. If you are able to tighten other timings, you can increase your lead.

Information comes from Here and Here found in Anandtech's RAM FAQ Sticky. The gist of the data is that raising the speed one step (IE DDR2 667 => DDR2 800 => DDR2 1066 ext.) while raising the CAS by one each step takes away all potential benefits to access time.

 

[idolwalrus]

great info!

So comparing what I wanted to do originally to your suggestion outlw6669:

1) Optimize RAM to a CL of 3 and underclocking to 667 mhz
Keeping 333 mhz FSB and a 3.0 ghz processor

compared to

2) Optimizing RAM to a CL of 4 and underclocking to 800 mhz
Overclocking FSB to 400 mhz rendering a 3.6 ghz processor


It seems to me too, that it's worth paying a 1ns lead for the boost in the FSB and processor. My concerns now would be safely overclocking (I can't help but feel nervous, this being my first time).

How much strain would overclocking my cpu FSB from 333 to 400 cause? Would I need addition cooling (other than the stock cpu fan and my 4 case fans)? I'm assuming I'd have to overclock my mobo too, so I'd have the same questions about that.

 

[outlw6669]

I would highly recommend your option 2.
Optimizing your memory will let you squeeze every last ounce of performance from your system but overclocking is the bread and butter of performance gains.

From all I have heard about the E8400, you should be able to run a stable 3.6Ghz at your stock VID (voltage identification), or just a little higher. You can locate your VID bye running a program like CoreTemp.

While I would recomend a better CPU cooler, even at stock, you should be able to push this overclock with the stock cooler. If, however, you have a spare $31.99 I would recommend a AC Freezer 7 Pro. Decent cooling at a reasonable price with simple instillation.

The C2D overclocking sticky would be a great primer for your first overclock. The procedure is very simple. In the BIOS, change your FSB to 400Mhz, your CPU voltage to whatever your VID is plus one step and check your RAM speed/timings. The P35 chipset is an able overclocker and will have no problem running at 400Mhz.

To test your overclock, use duel instances of prime95 in small fft torture tests. This will place an artificially high load on your CPU so you can ensure your temps stay reasonable and that your overclock is stable. In order to have 2 instances running, one on each core, you must edit 2 shortcuts to the program. If you right click and look at the properties for the short cut, you will see the line pointing the short cut to the actual program. At the end of this line, add a space and then -a0 to one short cut and -a1 to the other. This will allow the program to run twice, once on each core. To ensure 100% stability, I would again recommend running it overnight or while you are at work.

If you are getting errors with prime95, as long as your CPU is not overheating, raise your CPU voltage one notch at a time and retest until stable. Alternatly, you can lower your voltage one step at a time until you find the minimum voltage needed to keep a you overclock stable. Once you start getting errors, raise it two steps and call it a day.

As long as your temps are stable and your voltage is not to excessive, there is very little risk to overclocking. I would recommend keeping your voltage to 1.3v or less. It can go higher but this will give you plenty of Oc headroom and a safe limit.

 

[idolwalrus]

thanks, outlw, for all the great info and advice. I'll be putting it to use.