Confused about Extreme CPU's

[nrlanni]

I'm a nubb to OC'g so I've been reading and comparing my q9300 to various cpu's, including some extreme series versions (qx6700, qx9450, etc.).

For years I've read about Intel extreme series cpu's and I thought the big advantage was the unlocked multiplier, but a number of reviewers ran the unit with the stock multiplier and OC'd using voltage and FSB adjustments. Seems that one guys even had to adjust ram voltage.

I understand the cpu voltage adjustment - i.e., faster core = more voltage.

But I don't understand the FSB adjustment. I thought that the big deal with the extreme series was that the mult and the FSB were not locked, so one could dial in a different mult without having the make the other adjustments.

If a whole bunch of adjustments are required for the extreme series why spend the big bucks, and just tinker away with less "extreme" cpu's.

 

[szwaba67]

The main advantage of the unlocked multiplier is that you can get high OCs without high FSBs. Depending on your board, you may hit a wall with the FSB, if you have a locked multi, this means you also hit a wall with your CPU OC. If your multi is unlocked, then you could kick it up and potentially get more speed from your CPU. This is really beneficial if you have extreme cooling like a refrigeration unit, otherwise the heat will limit you. Nowadays, it's not worth getting an extreme CPU unless you plan to skimp on the board (lower FSB OCs), or if you plan on going all out with extreme cooling. But really, nobody who buys an extreme CPU plans to skimp on the board, that kinda defeats the purpose.

To be honest, I don't know what kind of gains you can get with the extreme CPUs even with extreme cooling.

 

[nrlanni]

I guess this is sort of a reality check for me becuase that's what I'd always read, but I wasn't aware that you still had to adjust the FSB.

What really confused me was that one reviewer commented that "the mult was unlocked" (yeh, that's expected for an extreme cpu) but when it came to overclocking, at least one or two reviewers didn't change the mult. but made OC adjustment in other areas.

 

[outlw6669]

As recommended reading I give you the Core 2 Overclocking Sticky.

CPU frequency is derived from FSB * Multiplier.
Taking the common Q6600 as an example, it runs at 2.4Ghz (2400Mhz) or 266Mhz FSB times it's 9x multiplier. The benefit of the EE CPU's is, as you stated, an unlocked multiplier.

Most Intel CPU's have locked multipliers that are only changeable between 6x and their stock setting. With the EE CPU's, you can change this to anything 6x and up. If there was a QX6600 (nonexistent Q6600 Extreme), you could easily overclock bye changing only the CPU voltage and multiplier. 10x would give you 2.66Ghz, 11x would give you 2.926Ghz and so on. As you can probably see, this would be quite easy to do and, as nearly all Core 2 CPU's have a high Oc headroom, would allow everyone and their grandma to have a high end CPU for cheap.

The far more common and arguably better way to overclock a CPU is to change the other variable, the FSB. This will allow any CPU to operate at faster speeds and also allow more data to be sent through the FSB each clock cycle. As most modern motherboards are certified to run their FSB at 400Mhz, this is a very viable option. Again, using a Q6600, if you change the FSB from the rated 266Mhz to 333Mhz you will achieve an overclock of 3.0Ghz (333*9). This is more desirable because it will allow 25% more data to be transferred through the FSB each clock cycle.

The downside to overclocking this way is that you will have to adjust many other settings, one of which would be the RAM settings.

The speed of your RAM is also determent bye the FSB. Depending on the chipset and BIOS on your motherboard, it will run at a ratio to the speed of your FSB. For ease of understanding, we will work with the ratio of 1:1 or having your RAM run at equal speeds to your FSB. In this example, we will look at overclocking with an E8400 (3.0Ghz, 9*333) with DDR2 667 RAM. With a 1:1 ratio, your RAM will be running at 333Mhz or 667 DDR. As the E8400 is an able overclocker, we will make a jump straight to 400Mhz FSB and 3.6Ghz on the CPU. At this FSB setting your RAM, linked to the FSB, will be running at 400Mhz or 800Mhz DDR. In order for your DDR2 667 RAM to run at the higher frequency you must, like the CPU, add more voltage. In reality, you will probably be using the more common DDR2 800 RAM so this realy only applies to overclocks past 400Mhz FSB.

If a whole bunch of adjustments are required for the extreme series why spend the big bucks, and just tinker away with less "extreme" cpu's.

The answer to your question is that some people have lots of cash and don't want to spend the time learning how to do a fairly simple procedure.

 

[szwaba67]

It's true that with an unlocked multi you don't NEED to OC the FSB. You can just up the multi and poof! OC! The voltage may still need to be adjusted and you need to cool it. Of course, who drops a grand on a chip and doesn't try to squeeze the other components for more speed as well?

Those articles you see where they don't touch the multi, I would assume they could acheive similar speeds by just changing the multi. So to answer that, I have no idea why they do that. I too would think the point would be to harness the unlocked multi as much as the other components, but who knows, maybe they just want higher FSBs =]

 

[nrlanni]

Got it - OC'g is more than just making the cpu turn a few more clock cycles. It's a about overall throughput.

This is no different than the days I raced cars - no matter how much horsepower you got, it has to be delivered to the ground in the form of forward motion. Taken to the next logical step, a Porche does the same thing with less effort and more finesse (i.e., learning to OC the right way).

If I remember correctly, that's what made Cray different from his colleagues in his day. They focused on making one or two parts of the system extremely efficient, but he said that you needed to look at all the bottlenecks.

Yes, I started reading the various newb's guides to OC'g, thanks. I think what got me on this issue was one of my pet concepts got harpooned!