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The Newbie's Guide to Overclocking.

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altec

polka dot ninja
Joined
Dec 23, 2002
Location
Doylestown, PA
Disclaimer: Overclocking, if done to extreme measures or if done with little knowledge of your computer can cause hardware damage that may be irreversible. I am in no way responsible for anything that happens as a result of your overclocking adventure. Make sure that you read this guide in its entirety so that you know what you should be looking for that could cause problems.

I have seen many newbie's asking for assistance in their first overclocking adventure, and I thought it would be nice to have a guide for them to be able to visit, so they can figure all of this stuff out. If you see anything wrong, mistyped, or misleading, let me know and I will be sure to fix it.

Ok let’s start off with the definition of overclocking. Overclocking is making your computer components work at a faster rate than they were originally meant to straight out of the box, so that you get more out of what you paid for, and have a faster computer. There are many ways to go about overclocking, but there is one really reliable way. Many of the newcomers to the forums ask if there is software to overclock, and yes there is. I do no trust these third-party overclocking utilities though, since it is much more reliable to change all of these settings in the BIOS, and it is a lot easier than you may think.

There are also many different things that you can overclock in your computer, but the two I will be focusing on in this guide are the CPU and the memory (specifically AMD CPU's). To overclock the CPU you will need to overclock the ram also to gain the best system performance that you can. To do this you will be changing a few main settings in your BIOS. The Front Side Bus (FSB), the CPU Multiplier, and different voltages. The FSB is the speed that the memory talks to the northbridge, which then in turn talks to the CPU. The CPU multiplier is a certain number that multiplies the FSB to give it the overall CPU frequency. Example: 10 (Multiplier) x 200Mhz (FSB) = 2000Mhz or 2Ghz.

Note: The motherboard, CPU, memory, and the PSU are generally the most important things in the system when overclocking. You do not want to skimp on these items if you are purchasing a computer that you are planning to overclock.

Currently the nForce2 motherboards on the market are the best because they offer a lot of features like the PCI lock that so many overclockers are enjoying at the moment Most of these motherboards, because of the PCI bus lock, can reach FSB speeds of 200Mhz or higher. PCI lock basically locks the PCI bus speed at 33Mhz so that you will not have to use dividers and worry about your PCI bus speed causing problems like hard drive corruption and other known problems that come along with running your PCI bus too far out of spec. My preference in the nForce2 boards that are out right now are the Abit NF7-S Revision 2, the Epox 8RDA+, the Chaintech Zenith, and the Epox 8RDA3+. All of these boards have confirmed PCI locks along with the Asus A7N8X and the MSI K7N2 Delta-L (The older MSI nForce2 motherboards do not have a confirmed PCI lock).

The current AMD CPU's that are holding the highest overclocks and the best price/performance ratios are the thoroughbred B 1700+, the thoroughbred B 2100+, and the newer Barton core 2500+. Some of the higher rated Barton core CPU's are also performing very well, but they are expensive so they do not fare well in the price/performance ratio.

Note: From what I am told, the newer Barton core, and Thoroughbred B core CPU's that are being manufactured by AMD have a lock on the multiplier, which makes them a bit more tedious to overclock.

You also will want to outfit yourself with a good high wattage power supply. Try to avoid the no-name brand ones that claim that they will offer 350W or 400W, because most of the time they will not, and will cause you instability problems along the way. The names that I trust the most are the Antec, Sparkle, and Fortron power supplies. They will all last a long time and give all of your components a good, steady supply of power. I have used an Enermax power supply for a good amount of time, and have had no problems out of it, but I have read from quite a few other forum members that they can be unreliable and their customer service is not up to par. You can use one, and they are a well know company, but apparently people have been having some trouble with their products. Use them at your own risk.

You should also be looking for good high-quality memory to support the FSB speeds that you want to be able to reach. There are many good brands of memory that will allow you to get to the speeds you want with some tight timings. The corsair XMS series, Kingston HyperX, and TwinMOS memory with CH-5 Buffalo Chips are doing to best at very high speeds. You do not want to skimp and go for a low rated stock speed like PC2100, PC2700, but want to look into some high-speed memory like PC3000, PC3200, or PC3500. These rating ensure that the memory will run at a higher speed like 200Mhz FSB, since that is the speed that they are supposed to run "out of the box". You can, however, get a lemon that will not run at it's stock speed, but have no fear because most higher-end memory manufacturers will rplace the bad memory batches that we sometimes get.

Cooling: It is a very good idea for you to invest in a cooler other than the stock one that comes with AMD processors. The stock AMD heatsink, as many people here on the forums say is nothing better than an expensive paperweight. When you begin to overclock and mess with your voltages, the on-die temperature of the CPU is going to begin to raise pretty quickly, and you are going to need something adequate to cool it off. If you want to stick with air-cooling instead of going exotic (water cooling, phase change, refrigerated water, etc...), or if this is the first time you are building a computer, I would recommend looking into the Thermalright heatsinks. In my opinion the SK-7, the SLK800, and the SLK900 are all doing the best for the amount of money they cost. You will need to couple these heatsinks with a very good fan with a high CFM (preferably more than 50CFM). A really good choice in fans is the Thermaltake Smart Fan 2, because it has variable speeds for up to 75CFM, and offers a reasonable noise level. The Thermaltake Smart Fan 2 also offers more static pressure than the Vantec Tornado, which makes it easier for the fan to push air through tightly finned heatsinks like the Thermalright SLK series heatsinks. If noise is not an issue, the Vantec Tornado is the highest CFM fan in the 80mm range, but is very very loud (It almost sounds like a jet engine taking off inside your case).

Another thing to look at is the air movement inside you case. You will want to use up all of the available bays that accommodate fans so that you will have a good cool ambient temp inside your case. when positioning your fans, most people will suggest that you put the exhaust on the back of the case toward the top, and the intake in the front of the case toward the bottom. The reasoning behind this is that heat rises, and the higher the exhaust fans are, the more hot air they are pulling out of the case. You will also want to clean the inside of the case pretty regularly, since dust will build up in there. Dust can accumulate and cause your temperatures to go up, or can absorb moisture that will slowly cause problems in your computer. I tend to keep 5 fans in my case, 3 intakes and 2 exhausts. The two intake fans are moving about 68CFM of air and the two exhausts are moving in the low 30CFM range.

FSB vs. Multiplier: Generally a higher FSB with a lower multiplier will give you better overall system performance than a lower FSB and a higher multiplier. This is generally the case because the faster that your FSB is, the faster the CPU can "talk" to the North Bridge, which then "talks" quicker to the memory. Even if you are loosing a few overall Mhz in your overclock to attain a higher FSB speed, it is generally worth it. Make sure to keep your PCI bus in spec though if you are running a motherboard that does not supply a PCI lock...nothing will console you if you end up corrupting data on your hard drive for those last couple Mhz on your FSB.

Unlocking: If you still feel that you can get a higher overall CPU speed, but your multiplier is maxed out, then you can unlock the CPU, but it will require a bit of modifying the chip. If you are using a Duron, then all you have to do to unlock the chip is connect all of the L1 bridges with a pencil. If you are using a chip with a Palomino core, then you will need to connect all of the L1 bridges with some conductive paint, or some window defogger paint (which you can purchase at your local auto parts store). To use the paint, you will need to fill the gaps with some crayon or super glue, and then use the conductive paint to connect the dots in between the L1 bridges. Most of the AMD CPU's with a thoroughbred core (A or B) are unlocked from the factory, but most of the motherboards that are out today will only recognize either the higher or lower multipliers. Assuming that the 8x bit on the motherboard is set to high which will give you the higher multipliers by default, you will need to connect the last (5th) L3 bridge to gain access to the lower multipliers. There are other methods to access different multipliers for your CPU and they require no modding to the chip itself. You can take small pieces of wire and insert them into certain pin holes on the CPU socket to make the motherboard recognize the different multiplier values. This method is a lot less permanent, but requires a little more knowledge of the CPU socket. A guide to do this can be found here: http://216.239.39.104/translate_c?h...raht/xp_unlock_draht.htm&prev=/language_tools. Here is another little page to help you to figure out where to place the wires in the socket: http://www.ocinside.de/go_e.html?/html/workshop/pinmod/amd_pinmod.html

This is the method I use to overclock a new CPU:

Make sure to go over your motherboard's manual thoroughly before you begin to overclock anything through your BIOS or jumpers. You will want to be farmiliar with all of the options that you motherboard has, like the location of the CMOS jumper, etc... If you do not have the original copy of the manual for your motherb oard, go to the manufacturers website and download a copy for reference.

1) Drop the multiplier to something like 5. If your motherboard does not allow you to adjust your multiplier this low, then you will have to settle for the lowest multiplier you can use. You can also unlock your CPU to gain the lower multipliers, but it will take some modding to the chip.

2) Begin to raise the FSB by increments of 5Mhz, testing with Prime95 and memtest86 until the machine becomes unstable. By unstable I mean that it creates rounding errors in Prime95, or errors in memtest86.

3) If you have an nForce2 board with PCI locks, you should be able to raise the FSB pretty high with some good memory. If you do not have a PCI locked motherboard, then you will have to use the dividers to regulate the PCI and the AGP bus speeds. It is recommended that the PCI bus should not exceed 38Mhz. If it does, you will either suffer from instability problems, or you will run the risk of corrupting the data on your hard drive, and you could loose some very valuable files, or even have to do a full format and reinstall. Running the PCI bus out of spec in any case can cause this problem, but most hard drives can support a PCI bus of around 38Mhz. Generally (but not always the case) if you have a motherboard with a 1/5 divider you do not want to exceed 190Mhz FSB since 190/5 = 38.

4) When the computer gets to be unstable with a high FSB, back it down slowly (1Mhz or 2Mhz at a time) until the computer regains its stability with memtest86 and Prime95

5) This should tell you roughly the maximum frequency that your memory can handle with the voltage and the timings you have it set on. If you want to see if you can get more move your memory voltage up a little, and relax the timings a little and see if you can squeeze some extra Mhz out of it. The majority of the memory that is on the market today will be able to handle a CAS latency of 2, but if you have to, use a CAS latency of 2.5. I never recommend going to a CAS latency of 3, as it will show greatly in your memory benchmarks, and will in essence cancel the benefit of the high FSB that you have attained.

6) Begin to move the multiplier up slowly and test with Prime95 and 3DMark 2001 until the CPU becomes unstable. You will know it is unstable when Prime95 encounters a rounding error (or any error of that sort) or if 3DMark2001 dumps you back to the desktop in the middle of a benchmark. If you want to use 3DMark2001 to test for stability, the best way to do it is to loop the benchmark for a good 45min - 2hrs and see if it dumps you to the desktop at all.

7) Back the multiplier down little by little and test with Prime95 and 3DMark 2001 SE until the computer is stable again. This should be the highest stable overclock you can get without changing the CPU voltage.

8) To see if you can get more out of the CPU begin to raise the CPU's voltage and move the multiplier up until you feel satisfied with the speed you are at. I usually try to make sure that the voltage that is going through my CPU is below 2.0v, and I feel that this is a good regulation, unless you have some more advanced methods of cooling (other than air).

9) If you are still not happy with the CPU speed, or feel like you could probably get more out of the chip than you have when you just tampered with the CPU voltage, there is always the option of toying with the memory's voltage to get higher FSB speeds, or on certain newer boards you can turn the voltage that is going to the chipset up, to help the motherboard gain stability at high FSB speeds.

Voltage Mod: There is a known problem with a lot of motherboards where they simply do not offer the high voltages that a lot of experienced overclockers use. One solution to this problem is another wire trick where you use the wires in the CPU socket to designate a certain voltage that you want. Like the wire trick for multipliers, this can be a little dangerous to the chip, so I would recommend making double and triple sure that you do this mod right. Since it requires a good layout of the pins and such, here is a thread that describes the voltage wire trick pretty well: http://forum.oc-forums.com/vb/showthread.php?s=&threadid=154172&perpage=30&pagenumber=1. Make sure to check all of the links, and the pictures so that you do not do anything wrong!

10) When you have completed all of this, run Prime95 for around 24hrs and make sure the computer is stable. Take a good look at the temperatures if you decided to tamper with the voltages, and try to make sure that they are under 55C. A good program to monitor the temperatures of different components in the computer is Motherboard Monitor 5. Another good stress test is Folding@Home. This will get my CPU hotter than any other stress testing program, and will be contributing to a good cause. The only problem with using Folding@Home for stress testing is that it will not tell you directly when you get an error in the program, it will just stop working, like Prime95 and memtest86.

Note: When testing the stability of a certain FSB or the FSB and proposed multiplier combination, I usually test for 4hrs. Then when I think I have all of the voltages and the different settings, I test for 24hrs (as stated in step 10). I am just clarifying that you do not have to do a 24hrs test with each different multiplier and FSB speed that you are trying out.

Burn-in: A lot of people feel dissatisfied with their overall overclock, and want to get more out of it when it seems that they have hit the wall. One way to try to get more out of the CPU than it seems you could originally is called burning in. Many people say that burning in will cause the CPU to last a shorter amount of time than it would have out of the box, and that it wont work. On the other hand, a lot of people have tried the burning in method and have had it work for them, me being one of them. If you decide you want to do a burn in, you will need to drop the overclocked frequency back down to the stock frequency of the chip and raise the voltage as high as you feel comfortable going. I think that it is a good idea to use between a .3v and .5v increase in the voltage for a burn-in. When I did my burn in I used a voltage of 1.9v, because my CPU is a DLT3C version, which designates it as 1.5v stock (about a .4v increase in voltage). Then you want to use Prime95 to stress the CPU for 24hrs - 48hrs. I am not too sure why this works, but the basic theory is that it is "breaking the chip in", and that is why it improves the performance. If you do this, make sure that you check on the temperature pretty regularly, and make sure it does not go over 50C - 55C. This could be very detrimental to the stability of the CPU during the burn in (which would defeat the purpose) if you let it go higher than 55C! Also remember that burning in does not work for everyone, but it has worked for quite a few.

Links:
You can find Prime 95 at: http://www.mersenne.org/freesoft.htm
You can find Folding@Home at: http://folding.octeams.com/index.php
You can find memtest86 at: http://www.memtest86.com/
You can find 3DMark 2001 at: http://www.madonion.com/download/
You can find Motherboard Monitor 5 at: http://mbm.livewiredev.com/download.html
Here is a link to BenchmarkHQ where you can find tons of benchmarking software, CPU indentification programs, and stress testers: http://www.benchmarkhq.ru/english.html?/b_e.html

If you have any further questions feel free to PM, e-mail me, or you may be able to catch me on AIM (my screen name is eatafatty).

Good luck
;)



P.S. Let me know if I left anything out. There is always room for revisions and I am looking to give the newbie's a good guide to refer to.
 
Last edited:
Bump

I know it is 3:00am, but doesn't anyone have any suggestions?

Thanks rugbyroy and Socket Eh? for the nice comments...;)
 
Altec, good idea.

I have some writeup on overclocking, don't know whether it is a good idea to post it here too. Pls let me know.
 
Added some stuff about folding, and where to find it.

Hitechjb1, if you have a guide also feel free to post it, thats what the thread is here for. :D
 
This is summary of what I learned and used in overclocking a Tbred B 1700+ DLT3C click link. Probably most of you already know about these techniques. If you think there are something missing or incomplete or incorrect, please post. But I think this may help some new comers to get start, ...

Latest revision:
Summary for overclocking CPU and FSB (page 3)



Summary for overclocking CPU and FSB

When overclocking a system, there are two major components.

1. CPU clock frequency
2. FSB clock frequency which is related to memory bus clock freq and ras/cas timing

The two can be optimized separately and resolved by the CPU multiplier (to the first degree).

First recent motherboard such as nforce2 can lock PCI bus and AGP bus speed, so assume PCI is locked at 33 MHz, so don't have to worry about HD and video card AGP bus running out of spec. For older mb whose FSB is running at a fsb:pCI ratio of 4:1 or 5:1, the max FSB is limited due to the PCI frequency should not exceed its spec too much. Usually 38 MHz is considered safe. E.g. if your mb only have a max 5:1 fsb:pCI multiplier, if max PCI is 38 MHz, you FSB is limited to 38x5 = 190 MHz.

1. CPU clock frequency: For a given CPU, it can be overclocked to its max frequency regardless of FSB speed, whether it is only running at 133 MHz or 166 MHz or overclock to 220-250 MHz (for the newer mb). So even you have to keep an older mb (that can run 133 or 166 FSB) for a while, don't get discouraged and can still overclock a powerful CPU such as the Tbred B 1700+ DLT3C or 2100+. The multiplier in the bios for AMD CPU will resolve that by

FSB x multiplier = CPU frequency

Assuming you have an unlocked CPU such as Tbred, e.g. if FSB = 200 MHz, you can set multiplier to 11.5 and so CPU, such as Tbred B 1700+ DLT3C or Barton 2500, can run at 200 x 11.5 = 2.3 GHz. Or if multiplier at 12, CPU would run at 2.4 GHz, or at 12.5, CPU would run at 2.5 GHz, etc, etc. Side track: some mb may cap the multiplier at 12.5 and you may need a mod to get to higher multiplier than 12.5. If needed you can find such info easily by a search.

CPU max overclocking frequency on air is mainly determined by
- the heat sink and fan (on CPU temp)
- Vcore and its stability (PSU rail and Vcore regulator cooling)
to the first degree, case and system temp secondary.

So for any system, assuming on air, if you have good heat sink such as SK7 (economical) or SLK-800U/900U and variable speed fan with speed 2500-5000 rpm that can push air up to 75 CFM (e.g. Thermaltake Smart Fan II) through the heat sink. Vantec Tornado fan has 84 CFM fan can cool even better, but a resistor mod in series w/ the fan is recommended so the fan speed/noise can be controlled. (Note that SLK-900U does not fit well physically on an A7N8X). The die temperature, such as Tbred B, should then be able to be kept under 50C at high level of oc. 40 C is even a more ideal temperature for oc frequency increase per Vcore increase (I estimated 100-140 MHz/100 mV for Tbred B 1700+ DLT3C). Always the lower the temperature the better, that is why water, thermoelectric, phase change, ... cooling come in. CPU fan speed can be lowered to between 3000-3500 rpm and the noise level is generally considered acceptable for 24/7 usage. AS3 or ceramique should help also.

Temperature is important not just because high temperature could damage the CPU (max temp from spec is actually much higher, 85-90 C for Tbred/Barton), more importantly lower temperature results in lower CPU leakage current which heats up the CPU drastically above certain temperature threshold (around 50 C), above which heat and current will positively feeding each other and the CPU will lose stability in oc'ing. Lower temperature means the chip can run faster, estimated (rule of thumb) around 0.4%/C for Tbred B/Barton. I did some calculation on various HSF, the difference between a HSF with 0.3 C/W thermal resistance (such as Vantec aeroflow, Volcano 7+) can be as much as 200-300 MHz lower compared to a SLK-800(U) (0.23 C/W). And with a HSF with 0.36 C/W (such as Volcano 11), the difference can be as much as 300-400 MHz+ lower, compared to SLK-800(U). Also I estimated that an increase in ambient temperature by 5 C (e.g. summer), there would be a 5-7% drop in max CPU oc frequency. Details are in another thread.

Good PSU delivers stable CPU Vcore (within +- 50 mV (AMD DC tolerance spec) at full Prime95 load), given the high active current surge at max oc within a very short period of time (possibly few CPU cycles). For high oc to 2.5+ GHz at 1.9V Vcore may require good PSU to source enough active Icore current so that the Vcore line, and the PSU 5V or 12V lines (depends on motherboard) that generates Vcore are stable (i.e. small line fluctuation). A7N8X, 8RDA+ uses 5V, NF7-S, 8RDA3+ uses 12V. As an example, a CPU running at 2.5 GHz 1.9V consumes 2.7 times the active power, and draws 2.1 times the active current of that running at 1.5 GHz at 1.5V.

I found that when choosing PSU, a major consideration should be shifted to current rating (on the PSU line that generates Vcore) for high level of overclocing, and not on the total power (watt) rating that most people seem to emphasize on and pay attention to when looking at PSU.

E.g. I did an estimate for a system with a Tbred B 1700+ DLT3C oc to 2.5 GHz 1.9 V, w/ video card such as 9700 pro, 2 HD's, DVD, CDRW, 1 CPU fan, 4 case fans, 2 memory sticks, ... for a nforce2 mb (such as NF7-S, 8RDA3+) which use 12 V to generate Vcore, the total 12V current requirement = 23.4 A +-. Total power is less than 350W. Many PSU's that look to have enough power may not have enough current for high level of overclocking. This number may vary a little bit (not a whole lot) due to component different. Detailed calculation in another thread. Look up the current spec for the good PSU's with enough current rating and small line regulation (e.g. 3% is better than 5%).

The Vcore regulator (those 4 or 6 big MOSFET's near the CPU socket are part of the 2-phase or 3-phase regulator) on mb becomes important when overclocking to high clock frequency (2.5+ GHz) which requires large active current. Mb that derives Vcore from 12V PSU line has better current sourcing capability, I think. Sometimes max oc may be limited by the Vcore regulator stability and cooling, this is something that may be overlooked.


2. FSB clock frequency: Mb such as those w/ nforce2 chipset, PCI freq is locked, they can go at least to 180 MHz. If you are getting new mb currently, mb with nforce2 chipset is a good choice, new rev 2 mb with C1 chipset stepping supports least 200 MHz officially.

FSB and memory bus frequeny are locked at a ratio. If the ratio = 1 or 100% it is called SYNC mode, and is recommended for mb such as nforce2. If the ratio != 1, it is called ASYNC mode where FSB and memory bus are running at different frequency but in locked steps.

How high can FSB go depends on
- memory rated speed
- chipset quality (stepping) and chipset Vdd
- chipset (both NB and SB) cooling

To get higher FSB, make sure the memory module is rated to handle the target FSB at a given ras/cas timing and voltage. E.g. PC3200 memory will support to 200 MHz FSB (or DDR400), PC3500 for 217 MHz (DDR 434), ...

For these RAS/CAS memory timing such as 6-2-2-2 1T or 6-3-3-2 1T. They refer to:
1. Active (to) Precharge Delay (aka Tras, tRAS) - usually 5, 6, 7, ... (Tras >= Trcd + CAS)
2. RAS to CAS Delay (aka Trcd, tRCD) - 2 is good, 3 is OK
3. RAS Precharge Delay (aka Trp, tRP, Precharge to Active) - 2 is good, 3 is OK
4. CAS Latency (aka CAS) - use 2 whenever possible
5. Cmd Rate (some bios does not have this, set automatically) - 1T is better than 2T

Memory timing should be set to 6-3-3-2 to begin with to get to as high a FSB as possible, then tighten it to x-3-2-2 or x-2-2-2 (where x = 5, 6), if possible but not necessary, after reaching max FSB. The difference between 6-3-3-2 and x-2-2-2 is minor (~2%) on overall system performance.

Regarding to SYNC (memory bus speed = FSB) vs ASYNC (otherwise), IMO, running slower memory in ASYNC at 50-66-75% is much more price/performace effective than 100% SYNC. 50% memory cost will get to 10-15% of the max bandwidth. This approach has been used in P4 dual channel since its FSB is QDR (quad pump data) and there is no fast memory to match at that speed, and dual channel is the only way to fill up the system bandwidth. But for AMD system which is DDR, in order to get absolute performance, one will have to use the fastest memory to match the FSB and run them in SYNC to get the last 10% of memory bandwidth.

ASYNC is a good feature for testing of the system. For example, if you have slower memory (for the time being), and you want to test whether the system can run at higher FSB, you can set them to fsb:memory = 4:3, so memory running at 166 MHz and FSB at 221 MHz. Or vice versa, if you want to test you fast memory (e.g. PC 3500 rated to run at 217 MHz), and you motherboard can only run at 200 MHz, you can set the fsb:memory = 3:4, so FSB = 160 MHz and memory at 213 MHz. Then you can adjust FSB at 1 MHz at a time above 160 MHz to see whether the memory can indeed run at spec of 217 MHz or beyond. You can use memtest86 to test the memory in ASYNC this way.

Dual channel or single channel mode in nforce2 mb is not that crucial for overall performance. The difference is only few % (say 2-3%) at most. Also single channel may let FSB to go a bit higher due to a smaller chance of potential dual dimm mismatch and memory controller stress at high FSB, I think. On the other hand, dual channel memory controller provides some performance advantage due to its intrinsic speculative caching capability. At this point, the little higher FSB from single channel offset the performance advantage of dual channel, and the two is about a tie, I think, for AMD mb. For some nforce2 mb that have integrated video which can benefit from twice the nforce2 memory bandwidth, since the bus between the video and the memory controller has 2x64 bit bus.

The max bandwdith between memory controller and CPU would be 2 x 8 x FSB = 16 FSB MB/s. x2 is because of DDR (data are transferred at both rising and falling edge of the FSB clock, x8 because of 8-byte bus or 64-bit bus). The effective bandwidth, taking into memory controller (~95% efficiency), would be around 15.2 FSB. E.g. FSB = 200 MHz, effective bandwidth ~ 3040 MB/s.

Dual channel makes a big difference for P4 dual channel mb though, due to quad pump data of P4 (or QDR). The max bandwidth for P4 dual channel is 4 x 8 x FSB = 32 FSB MB/s. The effective bandwidth, taking into memory controller overhead (~ 75% efficiency), would be around 24 FSB MB/s. E.g. FSB = 200 MHz, effective bandwidth ~ 4800 MB/s, which is around 60% more than that of a nforce2 mb running same FSB 200 MHz. E.g. running fsb:memory=5:4, with FSB=250, memory=200, effective bandwidth ~ 24 x 225 = 5400 MB/s.

Chipset Vdd and Cooling on FSB stability

If wanting to go higher, chipset Vdd and cooling may have to be looked into. But this is secondary compared to getting the correct memory module that is rated to run at the desired FSB frequency and timing.

Some new mb, such as NF7-S rev 2, has wide range voltage for chipset Vdd, Vcore, Vdimm, so no hardware Vmod is needed. Otherwise goto the individual mb section, there are lots of info about various Vmod.

Putting a passive heat sink on the SB with good air flow over it should improve stability at high FSB oc. Adding a fan on the heat sink of the NB (if there is no) and SB would be even better if wanting to go even higher FSB (220+ MHz).

RAID: One cons for recent nforce2 motherboard is that there is no direct RAID support for the traditional IDE parallel hard drives. RAID-0 delivers exceptional hard disk performance on older KT266/333 motherboards. The new serial hard drives are still not common and expensive. One can get two parelllel-to-serial converters to connect existing IDE (parallel) HD to the onboard SATA interface which supports only RAID-0 or RAID-1, but not for RAID-0+1.

Memory testing

Test the memory module using memtest95 at the rated frequency and voltage to make sure it runs at spec. memtest95 is running almost on bare hardware, outside of Windows, so the testing can be done without some uncertainty and stability issues related to chipset drivers, video drivers and intensive FSB traffic, ...

Another nice feature of new mb is that FSB and memory bus speed can be run ASYNC with each other, for memory and FSB testing to avoid having uncertainty for both of them. Set one of them slower and oc the other as much as possible to find out their limit separately. E.g. set fsb:memory ratio at 3/4, would allow you to test memory at 200 MHz while running FSB for sure at 150 MHz, etc, etc, ...

Summary

Even you have a motherboard running at slow FSB (133/166 MHz), you can still overclock the CPU to highest possible frequency, using high mulitpliers (assuming multiplier limit is resolved). That is, max CPU overclock frequency is independent of FSB. Max FSB overclocking does not depend on the CPU per se, since the multiplier can resolve that, assuming you have an unlocked CPU, such as Tbred. The best of both world is that you have a motherboard and memory that can achieve high FSB, and a CPU that can be overclocked to very high freqency.

Assuming you have a recent nforce2 rev. 2 mothboard, an highly overclockable CPU such as Tbred B 1700+ DLT3C, Barton 2500+, ... The nforce2 rev. 2 motherboard (such as NF7-S) is a good choice, since it has a wide range of voltage for Vcore, Vdmm (for memory), Vdd (for chipset FSB overclocking), Vagp than others, so Vmod is not needed in general. Further it uses 12V and 3-phase regulator both of which IMO are better for generate stable Vcore. If you have good heat sink (e.g. SK7 or SLK-800/900), adjustable high CFM fan, good PSU w/ enough active current sourcing rails and lines with small regulation (3% prefer), good CAS2 DDR PC3500 memory, then they are sufficient to get the CPU and FSB to above average overclocking, within 5% of the full potential of your system.

The last 3-5% would be more costly and may require more experience and technique and possibly better components. But probably at that point, one would have already acquired enough know how to get to the max oc and beyond.

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Adjusting FSB

The ideal situation is that both the FSB and CPU clock frequency are highest possible. FSB should be highest possible so system bandwidth (between CPU and north bridge for XP and P4) for memory and video are highest. Then CPU clock frequency would following FSB x multiplier by adjusting the multiplier. There is also some fine tuning at the end between the exact FSB (down to 1 MHz) and multiplier (down to +- 0.5), so as to tradeoff the final % between the FSB and CPU, since the exact CPU frequency may not be at the exact quantized level given by FSB.

At the beginning, keep the FSB close to its max (then the mulitplier has to be set to low accordingly, since multiplier = CPU_frequency/FSB). This number depends on your motherboard and memory. For recent rev 2 nforce2 mb, and if you have PC3200 CAS2 memory or better, 200 MHz is a good starting point. Then increase mulitplier to locate roughly the CPU max while increase Vcore 25 mV at a time. Run prime95 to check for stability.

Near highest overclocking, mulitplier is kept constant (or increase/decrease multiplier by 0.5 if needed, to allow room for FSB to change). FSB is increased/decreased 1 MHz or small steps (trial and error) until either the FSB or the CPU (or both but not likely) are maxed out (system unstable) for a given Vcore setting. The 3DMark01, 3DMark03 benchmark programs can be used to test the overall system stability, stressing FSB, memory, video in particular.

Sandra is a commonly used program for benchmarking CPU integer and floating point operations raw computing power in DMIPS and FLOPS, memory bandwidth, cache performance, multimedia performance, ... as well as some informations about system hardwares and devices.

For overclocking, don't use default setting. Set them to manual, so you can adust the FSB, mulitplier, memory timing (6-3-3-2 is a good starting point), ...

How to adjust Vcore

After finding the max FSB (or within 5-10 MHz), for CPU overclocking, CPU clock is increased (bigger step at beginning and few MHz step at the end). And when the system becomes unstable, you can increase Vcore by 25 mV stepwise to see whether it can make the CPU to run faster so that the system can become stable again.

Repeat the above until high Vcore is reached to a point that CPU clock frequency cannot go higher practically (say less than 5-10 MHz while temperature rises by 5C per step of Vcore (25 mV)), reaching zone of diminishing return on frequency. From experience, 1.9-1.95 V should be OK for typical Tbred B overclocking (at least for testing), system stability (e.g. running Prime95 for CPU overclocking) is key, while keeping die temperature under control (take 50-55 C loaded as reference rather than the perceived absolute limit). Good HSF is needed to keep temperature low.

There are different level of stability. Minimum is that it can boot in the operating system and run Sandra CPU. Prime95 is considered to be a reasonable way for CPU stability and stress test.

Overclocking is a process, not by sudden boosting the Vcore and hope it will go to 2.5 GHz. Then it would not blow up the CPU. Don't sudden jump Vcore by multiple steps since you will lose sight of the CPU stability and die temperature increases.

During this process, watch for
- system stability,
- rate of increase of clock frequency per step of Vcore increase
(I consider 5-10 MHz per 25 mV Vcore increase as near the overclocking limit)
- die temperature, keep an eye on the rate of temperature increase per step of Vcore increase
(I consider 5 C increase for loaded CPU per 25 mV step of Vcore increase as near the overclocking limit), take 50-55-65 C as relative rather than perceived absolute limit
- By combining clock frequency and temperature, the rule of thumb is:
10 MHz / C, at full load per 25 mV Vcore increase is about the break-even point for overclocking (point of diminishing return). Below 10 MHz / C is "easy" and economical for overclocking, above 10 MHz / C becomes harder and harder to overclock. And 2-3 MHz / C at full load is the limit.


Example for Vcore increase

Here use a Tbred B 1700+ DLT3C as an exmaple. If you have a CPU that can do 2.2 GHz @ 1.5V, it is a good CPU for oc.
(If you chip can only do 2.1 GHz @ 1.5V, then substract the CPU clock by 100 MHz and 0.5 in the multiplier in the following example, etc, etc.)

Keep FSB = 200 MHz
Raise the multiplier to 11.5, i.e. freq = 2300 MHz
Increase Vcore to 1.6 V+- should get it stable. Run prime95 to test stability.

Then repeat again with FSB = 200 MHz, multiplier 12. I estimate Vcore around 1.7 V +- to get it stable to 200 x 12 = 2400 MHz. Run prime95 to test stability.
etc, etc.

At the early stage, one would expect to get 100+ MHz for each 0.1 V or 100 mV Vcore increase. When close to the overclocking limit, that number will drop to around 50 MHz / 100 mV, and eventually down to 5-10 mV / 25 mV eventually, and the end is almost there. Also at the last % of overclocking, the temperature would increase much faster per step of Vcore increase, I consider 5 C/ 25 mV is about reaching the limit. It will be very costly in terms of voltage, power and temperature to get the CPU to run a % higher.

This is just an estimated scenario, try it out first. If you want to go further, you may need to try a better HSF such as SK7 or SLK-800U/900U with a variable speed high CFM fan such as TT SFII or even a Vantec Tornado (with VR mod).

When you can reach 2.4/2.5 GHz, depends on the HSF and PSU, your are probably 100 MHz away from one of the best oc of a 1700+ on air.
 
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altec said:
Wow hitechjb1, that looks a lot more indepth than mine...i feel inadequate now...:(

Don't feel that way. Yours is fine too. Look at how well it has been received. Mine may be too long and boring, ....
 
Lol, I wasnt being serious...good job on the write-up. You have to be one of the smartest people I have ever mat (sort of met). Thanks for the addition! :D
 
With all of the information hitechjb1 added, I think this should be a sticky for all of the newbie's. Should I try to contact a mod about it, or let them find it on their own?
 
Alrighty, I think I will do that now, maybe we can get a new sticky for all the n00b's out there. :D
 
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