5 tháng 5, 2008

Guide to Overclocking Intel Core 2 Duo Processors

What is overclocking?

Overclocking is pushing your CPU to run at a faster clock speed than the manufacturer has it set at.
What is involved?
FSB
For Intel Core 2 Duo’s typically you overclock by simply raising the FSB (front side buss). This speed is set at 266Mhz for the E6xxx-X6800. The FSB is set at 200Mhz for the e4xxx series. Raising the FSB is the only way to overclock your Core 2 Duo, unless it is an engineer sample chip or an X6800+ (Both of these have unlocked multipliers.)
Multiplier
To overclock your Intel Core 2 Duo by using the multiplier, you simply change that number to a higher number than its stock multiplier. For example an engineer sample chip E6300 has a multiplier of 7x, but you can change it to a higher value, say 9x. If you leave the FSB at 266, then 9x266 = 2400Mhz = 2.4Ghz.
PCI-E
When you overclock your CPU by raising the FSB, you not only overclock the CPU, but you also overclock your PCI-E. On most motherboards you can lock your PCI-E to 100Mhz (recommended).
RAM
By overclocking your CPU by upping the FSB, you also cause your RAM to be overclocked. But is that a bad thing? Yes and no. For cheap value RAM you can not overclock your RAM much at all. You would be lucky with 50-100Mhz. By simply changing your RAM/CPU divider you can adjust your RAM speed also. Typically a good stable overclock consists of the RAM and the CPU running at a 1:1 ratio. For example if your CPU’s FSB speed set to 400Mhz and your in a 1:1 ratio, then your RAM will show up as running at 400Mhz in the BIOS. Because it is DDR2 the RAM is actually running at 800Mhz effective, which is PC6400 stock speeds.
Socket 775 Motherboards usually support different types of DDR2 Memory. Motherboards natively support 533Mhz DDR2 all the way up to 800Mhz DDR2. It is possibly to run faster memory like DDR2-1000 and even higher like 1200Mhz, but this is only possibly by changing the CPU/RAM divider or overclocking the CPU via FSB.
When looking at RAM, and the speed of the RAM there are two things to take into account. What is the rated speed of the RAM? DDR2 memory typically ranges from 533Mhz to upwards of 1200Mhz. The memory frequency is not the only thing to look at when comparing the speed of RAM. The timings or latencies are also important.
Most value RAM has very “loose” latencies. 5-5-5-15 is quite common for value RAM. Mid end RAM is usually somewhere around 4-4-4-12. Mid-High end RAM has timings like 4-4-3-5 or 4-4-3-8. High end RAM will have low latencies like 3-4-3-9. The most important number is the first number. The lower the first digit the faster the memory.
By default, most motherboards will set the RAM timings to 5-5-5-15, so it is necessary to go into the BIOS and change these timings to the timings recommended by the manufacturer.
Loosening up your RAM timings will allow for a higher overclock. For example if your memory is rated at 4-4-4-12 and is PC6400 and runs at 800Mhz, then “loosening” the timings to 5-5-5-15, might allow for an overclock of upwards of 900Mhz. While at the stock 4-4-4-12, 850Mhz was achievable.
On some motherboards, like my Gigabyte DS3P, all the memory latencies and voltages are locked by default. To view these advanced settings in your BIOS, I pressed Ctrol+F1. This unlocked a hidden menu with advanced features.
NB (North Bridge) Straps
The northbridge has a series of straps. As you overclock, and the FSB increases the NB strap occasionally will change. What changes in the NB is the NB’s latencies. If you ever hit a wall and can not even overclock 1Mhz more then it quite possibly could be your NB strap. To get around this you could try a large jump of 10 or maybe even 20Mhz and see if your PC posts. If you are able to run your CPU and NB at a high strap with tighter timings, it is often times faster then running your CPU at a slightly higher clock. For example depending on the CPU, FSB, and multiplier a Core 2 Duo overclocked to 2.8Ghz may be faster than a CPU overclocked to 2.9Ghz. The NB strap idea is fairly new, and there isn’t all that much information out there.
Vcore (CPU voltage)
The CPU voltage is commonly referred to as “vcore.” The stock voltage for the Intel Core 2 Duo chips is 1.325v. When overclocking, almost always the voltage needs to be increased. But don’t increase the voltage unless you need to.
If you hit a wall and you can’t overclock any further then up the voltage a bit. I usually up it by my vcore by .025v. Once I reach an overclock that I am satisfied with, I will lower the voltage by as little as possible, until Orthos fails. This way I can figure out the lowest vcore required to run my CPU at the speed it is at.
The more volts you put through your CPU, the more heat it is going to create and the more watts it is going to consume.
It is not recommended to exceed 1.5v on air cooling, simply because temperatures are usually far too high. If your overclocking on water cooling or better cooling then 1.5v or a bit higher is nothing to be afraid of, as long as the temperatures are good.
Fans, heatsinks and thermal compound.
It is not recommended to overclock very much on the retail heatsink provided by Intel. It is a relatively small heatsink and will not handle large amounts of heat generated by a high OC.
It is recommended to overclock using an aftermarket heatsink. Some good ones include: the Tuniq Tower 120, Big Typhoon, Artic Freezer 7 PRO, Thermaltake Ultra -90, Zalaman 9700. Larger heatsinks have a larger surface area, and thus disperse heat a lot better than smaller ones.
To improve temperatures for any heatsink you can do a couple of things. First, be sure and use some good, high quality thermal compound such as Artic Silver 5. Second, you can lap your heatsink. Lapping is the process of sanding down your heatsinks surface. This gets rid of some of the small machine marks and tiny pits in the heatsink. Lapping is done by using different grits of sand paper – 400 all the way up to 2000 or higher. Lapping is not very hard but takes a lot of time and patience. Lapping a heatsink will typically yield performance gains ~2-8C.
Monitoring temperatures
There is a handful of software out there that will allow you to monitor the temps of your CPU. Probably the most trusted program is called TAT (Thermal Analysis Tool) and can be downloaded directly from Intel. It usually gives accurate readings for most Core 2 Duo CPU’s. It measures the temperature of both CPU cores and this data can be monitored by TAT.
Intel recommends that the temperature of both CPU cores does not exceed 60C. The general rule of thumb I follow however is I like to stay under 65C max load, because I know in every day applications I will never even come close to reaching 60C. Gaming, encoding and other tasks never fully max out both CPU cores at 100% full load like Orthos does.
Software needed:
To safely overclock, you will need some sort of CPU monitoring program. I personally recommend TAT. Other programs such as Gigabytes Easy Tune, can be terribly off. I had Easy tune at one time reporting negative temps, while on air cooling. Tongue
The second program you will need is Orthos. Orthos is a program designed to torture your CPU and put it under the most extreme conditions. It tests stability and halts and lets you know when an error has been detected. Orthos is a mod of Prime95. The earlier versions of Prime95 would not stress a core2duo CPU, because it was designed for single core processors. Orthos is a mod that basically runs two instances of Prime95 in one window.
Another piece of software that I’d recommend is Super Pi. Super pi is a small CPU benchmarking program. It doesn’t put nearly as much stress on your CPU as Orthos, but is a good program for monitoring increases in performance. Super pi calculates Pi – 3.14159… from 64k all the way up to 32M or 32 Million digits. Usually pi is calculated to 1 or 2 million digits for benchmarking purposes.
Another program that is not required but is recommended is memtest86. Memtest86 is a program that puts stress on your memory and will scan it for errors. If you are ever going to be overclocking your memory or playing with the memory timings, this program is highly recommended.
Lets Get started!
The first step is to enter your BIOS. To do this, boot up your computer and while it begins to post hit the Delete key.
There are two main ways people go about overclocking. The first way is by increasing your FSB by 10mhz at a time and running Orthos and monitory temps, and increasing voltage when needed.
The second way is to just jump into a moderate overclock. This is my favorite way, especially with the Core 2 Duo line and all of its potential. When I overclocked my e4300, I immediately overclocked from 2.4Ghz from the stock 1.8Ghz. I did this by upping my FSB to 266. I then ran Orthos and continued to overclock the FSB 10-20Mhz at a time until I hit a problem. Once I got an error or could not post, I’d add some vcore to the CPU. Then would boot up and run Orthos again.
When trying to figure out your CPU’s max overclock, set your memory to a 1:1 ratio. That way you are not putting unnecessary stress on your RAM. Once you figure on your CPU’s max overclock then play around with the memory/cpu ratio and tighten up your timings if needed.
What kind of overclock can I expect for my Core 2 Duo?
On high end air cooling, and the right RAM and a good overclocking motherboard, you should expect something around the following:
E4300 – 2.8-3.2Ghz
E6300 – 2.8-3.4Ghz
E6400 – 3-3.6Ghz
E6600 – 3.2-3.8Ghz
E6700 – 3.3-3.8Ghz
X6800 – 3.4-3.9Ghz
*NOTE* This guide is only the first draft. I'm sure it has plenty of errors. Please point them out as you see them, and I will make changes. Thanks!

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