Overclocking an E6700 - RAM Speeds....

[EtheAv8r]

I am afraid that even after some really helpful advice about RAM speeds, I am still somewhat confused about the maths formula, so maybe if I put down the specifics, some kind sole (kalniel?) may provide the numbers / formula / explanation. I have a real mental block with this, simple as it seems to be for everyone else!

I have an E6700 which at stock runs on a multiplier of 10 and has a CPU clock speed (aka FSB or frequency) of 266 MHz and so 10*266 = 2.67 GHz CPU Speed.

To run this at full speed I understand that I need PC 4300 running at 533 MHz (2*266) – so where does the ‘quad pumped’ bit come in, which I understood meant an FSB of 1064 (4*266)?

I plan to overclock this E6700 and have a target of 3.66GHz, which I understand is quite achievable, by raising the CPU Clock frequency from 266 to 366, increasing the Memory voltage to (2.0v for Corsair PC8500), increasing the CPU VCore to 1.35, plus a few other settings.

What I don’t understand is what speed memory I now need, is this 366*2 = 732 so PC6400 (800 MHz) is the minimum with RAM running synchronously? - but if I run a 5:4 RAM:CPU clock ratio (732/4*5 = 915MHz) then I need PC8000 (1000 MHz) or even PC8500 (1066Mhz), or if I have PC6400 RAM that overclocks well, I have to increase the RAM Voltage and maybe loosen the RAM timings and set the DRAM Frequency as “DDR2-PC1098” in the BIOS?

Of course I may ‘only’ get to a CPU clock of 350….. or less, but I am not sure I understand what RAM timings this overclocking produces. If my numbers in the preceding paragraph are correct, maybe I have sort of stumbled on it, but if they are not correct I am clearly ob the wrong track.

[Hottentot]

What I don’t understand is what speed memory I now need, is this 366*2 = 732 so PC6400 (800 MHz) is the minimum with RAM running synchronously

Thats your answer, the only caveat is that you may not reach it (3.66GHz) and if you do you will need good cooling. Running the RAM synchronously is also the optimum solution.

[EtheAv8r]

OK thanks.

What puzzles me therefore is why some people use higher speed RAM, or overclock their RAM if running 5:4 ratios, if such a high overclock running the RAM synchronously - could therefore theoretically go up to 4GHz (10*400) - is available with PC6400 (800 MHz) RAM, which is so much cheaper than the higher speed RAM?

[chrestomanci]

The faster the ram runs, the faster the data comes out of it, so all other things being equal, it is best to run the Ram as fast as possible so your CPU is not starved of data.

However, the north bridge has to talk to both the Ram and the CPU (via the front side bus). It cannot operate asynchronously, there must be a simple ratio between the clock rate of the memory bus and the clock rate of the frontside (CPU) bus. This is where the 5:4 ratio comes from. For every 5 clocks on the ram bus, there are 4 on the CPU bus. The north bridge will only support certain ratios. 3:2 will be another if you can get fast enough RAM.

Quad pumping relates to how data is transfered across a bus, such as the one between the CPU and the north bridge. A bus will contain one clock line that has on it a square wave wave form like this:
_#_#_#_#_
There are also a number of data lines, and a number of lines that indicate who owns the bus, so who is speaking and who should be listening.

Traditionally, data is only sent on the rising edge of each clock pulse. That is, each time the voltage on the clock pulse rises from low to high, the reading end should look at the value on each data line.

When DDR Ram was invented, and the AMD athlon came out, the data rate was increased by transferring data on the falling edge as well. That is the reading end has to look twice per clock cycle for new data. Doing it this way instead of just increasing the clock rate simplifies some parts of the electronic design of the motherboard.

When the Intel P4 came out, it had a Quad pumped data bus so that data is sent our times per clock cycle. Personaly I think this is a bit OTT, and was probably done more for marketing than for electronic design.

[kalniel]

I think you've got good answers already

In my previous explainations I have sometimes ignored Intel's 'Quad pumped FSB' because it just confuses the issue. All you need to know about it is that to run a core 2 duo you need a motherboard that can provide a quad pumped FSB, or 1066mhz. It's somewhat equivalent in function to AMDs Hypertransport which also boosts the speed at which the CPU connects to the rest of the system. However Hypertransport's real quality is that it's a 'standard' way of connecting things, so you can use it to connect other things as well. Aside from that you can pretty much ignore it and concentrate on the CPU clock.

What I don’t understand is what speed memory I now need, is this 366*2 = 732 so PC6400 (800 MHz) is the minimum with RAM running synchronously? - but if I run a 5:4 RAM:CPU clock ratio (732/4*5 = 915MHz) then I need PC8000 (1000 MHz) or even PC8500 (1066Mhz), or if I have PC6400 RAM that overclocks well, I have to increase the RAM Voltage and maybe loosen the RAM timings and set the DRAM Frequency as “DDR2-PC1098” in the BIOS?

*nods* You're right, but as others have said, there's not much reason to. Faster running RAM can boost performance a little, but you have to ask if the money spent on that RAM could be better spent on improving something elsewhere that will give you a bigger performance gain.

Graphics card aside (this is where you get the biggest gain in games), only when you run out of CPU overclocking should you then worry about spending above the odds on RAM to gain an extra %.

*If* DDR800 ram is only a few quid more expensive, then sure, why not run it at 5:4 and run the ram faster? But there's a point where you do just have to say 'how much am I willing to spend to get only a limited return'

[EtheAv8r]

Thanks, now things are clearer, and I see I was getting there with my understanding of RAM/FSB speeds - but being 'old' was confused.


I now have an E6700.

I need to finalise my motherboard choice - waiting for ASUS and ABIT 680i launch & reviews before final decision... as these potentially allow me to lower the multiplier and try out higher FSB speeds during the OC process - reports are that there is a 'wall' at about 350 for some MBs, but if you go over 401, then the wall comes down!

[EtheAv8r]

In order to make the calculations easy (and not have to remember how to do it in future), I have produced a spreadsheet, so all I have to do is enter the variables (Multiplier and Clock Speed) to produce the Processor speed and RAM Speed for any combination.

Next - motherboard choice....