Overclocking Memory+FSB Ratio

[GentaiShinigami]

Greetings,

I am trying to do a very mild overclock on my pretty old rig atm. The motherboard supports un-linking the RAM and CPU which I'm told is good, but I'm not sure what settings would be OK as I've heard something about your FSB and CPU needing to have a certain ratio, but didn't totally understand what they were talking about. My mobo doesn't support changing the multiplier or anything like that just the FSB which is currently 800.

Currently my CPU is a Pentium D 2.8 Prescott, and my Mobo is an ECS NF650i SLIT-A. My RAM is Corsair TWINX2048-6400C4PRO which is two matched 1gb sticks running at 800mhz with 4-4-4-12 timings.

The problem comes in when I split them up because my mobo doesn't support any higher voltage than what is required to run the RAM at it's recommended spec of 800 (it's actually just a hair lower than what is required, but it seems to run it fine and has for years). This means I can't run the RAM any higher than it is due to not being able to deliver more voltage. When everything is set to auto the FSB is set to 800 and the RAM 800 at a 1:1 ratio. I'm not sure what to do if I bump the FSB up to 860 which takes it to ~3.0ghz then will the ram being 800 cause a problem (cause I can't raise the RAM to meet 860 due to voltage)? Also, which voltage is required to be raised when I bump the FSB up as above. My mobo has an option for either the FSB voltage or the CPU Core voltage.

I would GREATLY appreciate any help as this rig is old, and being stressed hard by current games, and I don't have the money to upgrade it right now unfortunately. Temps aren't a problem as my CPU is running at a steady idle 15c, and 18-20c under load (<3 Antec 900 with max fans on high). Thanks for your time, and if other info is needed just let me know.

[Purrrfect]

If the ram is only 800mhz then its a crapshoot as to how high you can make it go, especially if you don't have dram voltage adjustments. You can try raising dram timings if you have access to those, that may ease it enough to run. Can you change the ratio? Something like 3:5 or something may let you clock the ram down and the cpu up.

[GentaiShinigami]

Yeah, I can unlink the FSB and RAM and make it whatever I'd like. I just don't know enough about it to know what kind of ratio would be good to use or if overclocking to CPU would be worth it if I have to drop the RAM speed down to like 533 or something. Also not sure which voltage to raise on the CPU when I do raise it. There is an option for the CPU Core and one for the FSB voltage. Currently I'm at a 1:1 ratio at 800/800 CPU/FSB which is the factory defaults. 860 FSB puts me at just barely over 3.0ghz so what would be the best thing to do with the RAM at that point?

Thanks for taking the time to help I appreciate it a lot.

Edit: I do have RAM Voltage adjustments, but to make the RAM reach the EPP 4-4-4-12 timings you have to raise voltage from default 1.8 to 2.1v, and my board caps at 2.1v so I have no room to go higher.

[Purrrfect]

I don't know for sure if it's better for you to go with lower ram timings or higher timings with a higher frequency, but I think the latter will work better for you.

However, reading your last post again it sounds like your ram might be locked to your fsb, and you can only change a ratio of the fsb to the speed used by the cpu multiplier to create cpu speed. In that case your options are a bit limited. You should try putting it all to factory settings and then changing just the ratio numbers and use cpuz to find out what changes and by what factor to see where you can go. If you try various ratios and your ram speed never changes then you're pretty much limited on the fsb speed to whatever the ram likes, at which point raising ram timings might allow a higher fsb speed. I think some ddr2-800 ram I had in my last pc I managed to run at like 930 or something with lenient timings.

[GentaiShinigami]

However, reading your last post again it sounds like your ram might be locked to your fsb, and you can only change a ratio of the fsb to the speed used by the cpu multiplier to create cpu speed.

Firstly, thanks for taking the time to help me out I appreciate it. Also, apologies but I don't understand fully what you mean here. Perhaps you could elaborate further for me? The only number I can type if I un-link the FSB and RAM speeds is a number that is currently 800 which reflects a 2.8ghz speed on the CPU. If i type 860 in that box it raises the CPU to 3.0ghz clock roughly, but affects nothing else.

If I instead use Linked mode I can both set the above number and pick from a list of ~5 ratio's as well. So I could set it to 860 3.0ghz clock and it would adjust the RAM speed (mhz) to match whatever ratio is selected. My problem is I don't know which ratio is the right one, and I don't know if leaving the ram unlinked @800mhz while I keep bumping the CPU up in speed is OK (safe?). I would just 1:1 link them but like I said I'm out of voltage increases to raise the RAM further so that's a no go.

Then the very last problem I'm having is knowing which of the two voltage changes is the one I need? I don't remember having read or heard about a FSB voltage before just the CPU Core voltage. When I unlinked and did ~830 (2.9ghz CPU) and 800 RAM it ran fine w/o any voltage change. When I bumped it up to 860 (3.0ghz CPU w/ 800 RAM) it started BSOD'ing. I'm guessing either my ratio caused that or that I need to supply more voltage to the CPU I just don't know which voltage to work on increasing in increments. The FSB or the CPU Core voltage.

Again thanks for your time and help, and apologies if I'm explaining this poorly. It's hard to explain things over the net sometimes. >_< I'm going to include my CPU-Z at defaults below and restart and jump it to 2.9GHz and report the changes since I know I can do 2.9 stable w/o voltage changes.

CPU-Z Info at defaults (w/ RAM "overclocked" to its EPP settings):

Under Processor:

• CPU: Intel Pentium D 920 2.80 GHz Presler - 65nm
• Core Speed: 2800.1 MHz
• Multiplier: x14
• Bus Speed: 200 Mhz
• Rated FSB (the only number I can change in BIOS): 800 MHz
• Core Voltage: 1.248 V

Under Memory:

• DRAM Frequency: 400 MHz
• FSB:DRAM: 1:2
• CL: 4
• tRCD: 4
• tRP: 4
• tRAS: 12
• tRC: 22
• CR: 2T

[GentaiShinigami]

OK, just got through in BIOS and here's what info I've got to show, and bolded an important question below.

On Expert mode (unlinked RAM/FSB) the RAM can never be higher than the FSB (I'm sure that probably normal, but just stating anyway). The highest voltage I have for DRAM is 1.95v which it is currently at (this was always a problem because the EPP for my timings of 4-4-4-12 is at 2.1v lol.) The RAM has always been stable so I just rolled with it. The JEDEC recommends 1.8v for its 5-5-5-18 timings btw. The current "CPU FSB" voltage is 1.20V and can also choose 1.30V or 1.40V. "CPU Core" voltage goes up to like 1.70V I think i was and I think it's currently at ~1.20V (can't remember fully).

Currently as I write this I sit at 829 FSB and 829 RAM (414.5 MHz w/ DDR). I've never done 829 on linked before because I was scared to raise RAM any higher, but it's seeming to be stable thus far though it certainly needs more testing. Is there danger in under-volting something if it runs fine?

Here is the new CPU-Z info using Linked Mode (FSB and RAM Linked on AUTO ratio) at speed of 829 on each:

Processor:

• Core Speed: 2901.5 MHz
• Multiplier: x14
• Bus Speed: 207.3 MHz
• Rated FSB: 829.0 MHz
• Voltage: 1.216~1.248 V (It floats a little in CPU-Z)

Memory:

• DRAM Frequency: 414.5 MHz
• FSB:DRAM: 1:2
• CL: 4
• tRCD: 4
• tRP: 4
• tRAS: 12
• tRC: 23
• CR: 2T

[levish]

Drop ram to the 533 speed from 800 to give you some headroom, heck you can even go down to 400 if the processor will overclock that high to eliminate RAM as a overclock bottleneck.

before stress testing the cpu pop a memtest86 disc (can downlod the iso free from their site) to make sure the RAM isn't out of spec.

http://www.legitreviews.com/article/102/1/
Used 1.45 vcore to hit 3.5Ghz
http://www.compymcputer.com/uploads/1892895731.jpg
Used 1.5 or 1.55 vcore to hit 4Ghz

Obviously you need a pretty beefy cooler to keep a toasty processor like yours under control while overclocking

Its a crap shoot as to where you can get and requires some research, I'd start by checking for links specifically to your motherboard. Make sure to do stability testing for 30min to 1hr.

[GentaiShinigami]

Wow, first just let me say THANK YOU! Was beginning to lose hope that I'd get any more responses. I'll be sure to do all that, and check out those links. Was waiting to go any higher till I had a definite answer about which voltage should be raised. I've never heard of CPU FSB Voltage adjustments, but then again I'm new to OC'ing.

I'm not wanting anything stupid high I just want to get some more "oomph" out of this CPU before I upgrade it this winter. My CPU mildly OC'd (as stated above) at 2.9GHz is running at (with an ambient temp of 25c) 23c under full load, and my 8800 GTS 320 factory Superclocked as well as OC'd to 677 Core, 1586 Shader (linked), and 992 Memory is running 63c under full load. So my Antec 900 (5 120mm fans and the big 200mm on top all on high) is definitely doing it's job, and hopefully will allow me something like 3.5GHz OC. CPU cooler is a meh Artic Cooler Freezer Pro 7.

As a final question what would be an ideal ratio to keep between my ram and my CPU? Other than that looks like you've covered it all for me. Thanks again for the help and your time as well as thanks to Purrrfect for the same!

[Cephius]

As a final question what would be an ideal ratio to keep between my ram and my CPU? Other than that looks like you've covered it all for me. Thanks again for the help and your time as well as thanks to Purrrfect for the same!

For stability's sake it's often best to keep the locked ratio between your RAM and FSB.

[GentaiShinigami]

For stability's sake it's often best to keep the locked ratio between your RAM and FSB.

Mmmm in that case that'd be a 1:1 in my BIOS. I can do Linked and change the ratio itself, but on AUTO it is a locked linked 1:1 ratio. That will cause problems cause I'd require RAM speeds of ~1000 (rough guess) with a FSB of ~1000 to get a OC of 3.5 GHz. Don't think 1.95v is gonna take my DDR2-800 to 1000 lol. :( It's stable currently at I think it was 829 I wrote above. Been running on it since I made that post putting mass hours on Dragon Age and haven't had any hiccups yet and it's been on 24/7. Maybe I can get the RAM to get up to ~3.0-3.2 at least on the volts I have.

Do you know if their is a danger in under-volting my RAM if it runs properly and displays no errors or problems? Also, thank you as well for your help Cephius it's much appreciated. \^^/ Gonna try out 3.0 tonight after raising the CPU Core Voltage a step since last time it BSOD on me doing a 3.0 OC on stock voltage.

A lot of the reason I'm trying so hard to get the CPU performance to increase isn't so much the framerate in games it's because these stupid ass Creative headphones start to crackle when the CPU is under super heavy load. Of course this is usually accompanied by lagging FPS, but sometimes I can be doing ~39 FPS (or more) and still get it (usually when particle/plasma effects are on screen like fire or glowy stuff). I can use normal headsets straight out of my speakers with no crackle, but the damn Creative ones sound sooooo freaking good and are so comfortable it makes other headphones a non-option. I just ended having to deal with it. -_-; Would be awesome if Creative could make a damn driver that wasn't rubbish...

[Cephius]

There's nothing wrong with undervolting as long you're stable. If the RAM doesn't get enough power you'll know it because you'll crash and blue screen frequently. You should always seek to use as little voltage as possible, because excess voltage means excess heat, and heat is the enemy for any overclocker.

Just remember to test test test after you change anything and always monitor your temperatures.

[GentaiShinigami]

There's nothing wrong with undervolting as long you're stable. If the RAM doesn't get enough power you'll know it because you'll crash and blue screen frequently. You should always seek to use as little voltage as possible, because excess voltage means excess heat, and heat is the enemy for any overclocker.

Just remember to test test test after you change anything and always monitor your temperatures.

Awesome, exactly what I was needing to know. Thank you sir! ^^/

[levish]

you can try loosening ram timings if you insist on not dropping the ratio, for example 4-4-4-8 try 5-5-5-10 or 12.

your best source of information would be to look at what other people are using for settings for the same model motherboard and processor to get a range of where your values should be.

[GentaiShinigami]

Well, so far 3.0GHz at a 860FSB+RAM speed is holding stable w/o any voltage bump needed. Been going good for ~2 hours now. Will stress test it when I wake up more, and comb through the links Levish kindly posted for me earlier. Last time I tried 3.0 it didn't fly, but I had the FSB unlinked from the RAM which was still at 800 so that didn't turn out so well (BSOD's). Guess I'll keep climbing till the RAM starts giving me problems. My CPU currently doesn't go above room temperature @3.0GHz at it's max so seems I still have some room to explore. Thanks again guys. I'll edit this post tomorrow early when I get a chance to do more work with it. Until then~ ^^/

Edit: And yeah I suppose first thing I'll try when RAM starts giving me problems is to drop the timings to the JEDEC2 profile of 800MHz 5-5-5-18 @1.8v rather than the EPP profile at 800MHz 4-4-4-12 @2.1v (supposed to be but im capped at 1.95v lol, w/e it works). I'll have a .15 buffer then to raise it for matching the FSB. If I really want to lower RAM speed the JEDEC1 profile is 540MHz 4-4-4-13 @1.8v so guess I'll just stick with those two speeds and timings for now since they are the built in recommendations and I'm a nub at this.