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Core i7-3770K is slower than i7-3770

DBP

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Well, the title tells part of the story, anyway. The i7-3770 at its stock configuration is faster than a non-overclocked i7-3770K. Don't believe me? Read on.

The i7-3770 is described by Intel as a 3.4 GHz CPU (with turbo to 3.9 GHz) while the i7-3770K is 3.5 GHz (again with turbo to 3.9). So it's natural to assume that the 3770K is faster. I've seen people configure a system with a 3770K even though they're not going to overclock it just for that extra 3% of CPU speed. In fact most of the time it's 5% slower! How's that? It's all about the turbo.

Turbo Ratios in the i7-3770K:
Overclockers quickly become familiar with the Turbo ratios you can set in the BIOS. By default the 3770K has:
  • A 1-core ratio of 39x.
  • A 2-core ratio of 38x.
  • 3-core and 4-core ratios of 37x.
With the default base clock of 100 MHz, this means that if only one core is active the CPU will be clocked at 39x 100 == 3.9 GHz. But that's only if 3 cores are idle. If a second core is active the clock reduces to 3.8 GHz, and so on.

However, it's very rare for OS X to turn off cores. Even if you've got one process chewing 100% CPU (visible in Activity Monitor) it's common to see the load spread across the cores (visible in Activity Monitor's CPU History window for example). Most of the time under load an i7-3770K is a 3.7 GHz CPU.
Intel don't publish the default 1/2/3/4-core ratios, just saying "up to 3.9 GHz". And they say the same for the i7-3770.

My first i7 CustoMac was an i7-3770K (on a GA-Z77X-UP5 TH motherboard) and after overclocking it to 4.4 GHz (mainly by increasing the turbo ratios to 44) I was familiar with the way turbo worked in the 3770K. But when I started working with an i7-3770 system (on a GA-Z77-D3H motherboard) I quickly noticed something different.​

On the i7-3770 all four turbo settings are 39. So with all four cores "active" (as OS X tends to do) an i7-3770 is a 3.9 GHz CPU.
Now it's possible that the motherboard BIOS is bumping up the turbo settings from the chip's own default (after all, it might make the board seem to benchmark as faster than others?) but if that was the case why wouldn't the boards also do it when using i7-3770K CPUs?


I've confirmed this with HWMonitor, and by observations of increased Geekbench Integer and Floating Point results with the non-K chip. On the i7-3770 the CPU runs at 3.9 GHz. On a non-overclocked i7-3770K it runs at 3.7 GHz (very very occasionally jumping up to 3.9 GHz for single-threaded workloads).

Of course, the K processor can be overclocked further than the non-K, so once you start overclocking any slight advantage the non-K chip had quickly disappears. Also note that raw CPU speed is not the only thing affecting the performance of your computer, so "5%-slower" CPU does not mean your computer would be 5% slower. RAM, I/O, GPU, networking, all these things come into play.

The bottom line is that the difference is very minor, but if you're considering what chip to purchase for a new build and you're not intending to overclock, don't assume that the more-expensive 3770K will be better!​


Do you think I missed anything? Have you observed situations where the K is actually faster than the non-K when you weren't overclocking? And yes, I know it's actually possible to change the turbo ratios of the non-K CPU!
 
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Interesting read, thanks for your efforts. :)
 
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Ok, so they're supposed to be the same. They're not. On a GA-Z77-D3H with BIOS F18 (the latest non-beta BIOS, from August 2012) they all default to 39. And they're tweak-able up to 43.
To me this is just another BIOS bug. And here is a simple but likely explanation: The spec update is stamped with "January 2013" and your BIOS was developed back in 2012. Maybe they missed a few important pages. Don't forgot. You have an Intel processor, designed and manufactured by Intel, and they write the specs. Not Gigabyte or some UEFI BIOS developer.
 

DBP

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Thanks for pointing out the documentation where Intel does in fact specify turbo rates for all its processors. Good to know. But don't lose sight of an underlying issue.

While boards that overclock the chip (to 39,39,39,39) by default do exist in the wild and therefore the chip can "by default" be faster, even if they didn't exist that would still mean that:

The (cheaper) i7-3770 is at least as fast as the i7-3770K before overclocking. And it includes Vt-d virtualisation tech (although irrelevant for most uses) as well as the Vt-x that they share.​

It also seems that those boards that allow you to overclock the i7-3770 (up to 4.3 GHz if you're lucky) are also outside the spec. But they exist. Actually, I haven't done an exhaustive survey to determine if the specific i7-3770 chip plays a role in this, but the fact remains that if you're not going to OC then there's no advantage in the i7-3770K other than having the option to OC later.
 
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Thanks for pointing out the documentation where Intel does in fact specify turbo rates for all its processors. Good to know. But don't lose sight of an underlying issue.

While boards that overclock the chip (to 39,39,39,39) by default do exist in the wild and therefore the chip can "by default" be faster, even if they didn't exist that would still mean that:
The (cheaper) i7-3770 is at least as fast as the i7-3770K before overclocking. And it includes Vt-d virtualisation tech (although irrelevant for most uses) as well as the Vt-x that they share.​

It also seems that those boards that allow you to overclock the i7-3770 (up to 4.3 GHz if you're lucky) are also outside the spec. But they exist. Actually, I haven't done an exhaustive survey to determine if the specific i7-3770 chip plays a role in this, but the fact remains that if you're not going to OC then there's no advantage in the i7-3770K other than having the option to OC later.
I don't think any boards allow multiplier overclocking of 3770's (non-K...assuming your referring to this post...http://www.tonymacx86.com/overclocking/87693-slightly-overclocking-i7-3770-ok.html).

As for the chips being equivalent performance wise, excluding overclocking, that's absolutely true, and I don't think that's a secret. Intel even markets them as such.

In regards to your particular case, did you do use msrdumper to see what's actually happening? If the non-K is using 39 all core, and the K stock bins, I'd say that is a BIOS error (not on your part, on GA's...probably meant it the other way around). I'd also bet a lot of money that just because you can change the multiplier in the bios to 43, it won't run above 39 on a non-K. Some boards let you change the the multipliers for e5-Xeons in bios, but it doesn't have any effect as the multiplier table is locked (you can also enable Vt-d in BIOS for K version cpus...).
 

DBP

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As for the chips being equivalent performance wise, excluding overclocking, that's absolutely true, and I don't think that's a secret. Intel even markets them as such.
No they don't. Marketing is about the message, not the fine print.
They market one as a "3.4 GHz" processor, the other as 3.5. Yes the fine print for both mentions turbo boost to 3.9 GHz, but purchasers do look at those 3.4/3.5 numbers and see a difference, even though it won't affect them (we live in "a turbo world", and more to the point in an "all cores active" turbo world).


In regards to your particular case, did you do use msrdumper to see what's actually happening? If the non-K is using 39 all core, and the K stock bins, I'd say that is a BIOS error (not on your part, on GA's...probably meant it the other way around). I'd also bet a lot of money that just because you can change the multiplier in the bios to 43, it won't run above 39 on a non-K.
In this machine, the default setup looks normal:
default_clocks.jpgStatus_at_3_9.jpg
The status there showing all cores at 3.9 GHz may be confusing because we don't know for sure which multiplier (1/2/3/4-core) is active in the BIOS at the time.

No I haven't run msrdumper to sample p-states, but HWMonitor reports the multipliers just as well. In fact it multiplies those out to display MHz in the history window. Here you can clearly see "3900 MHz" as the machine winds down from a Geekbench stress test (all cores were busy):
HWMonitor_at_3_9.png
On the 3770K machines I've used this doesn't go above 3700 MHz without overclocking.

I had a play in the BIOS and set all the turbo clocks to see how high they would go (43, 43, 42, 41):
max_clocks.jpg
Note that I didn't use this config, but I could effectively run this CPU at 4.1 GHz.

As it's using the stock Intel cooler, it's a machine I'm using for work, and I didn't want to stuff around with voltages for this quick test, I figured I'd at least play with setting them all to 40 to see what happens. And guess what?
Status_at_4_0.jpgHWMonitor_at_4_0.png

Finally, here are Geekbench runs from 3.9 GHz and 4.0 GHz:
i7-3770_at_3_9.pngi7-3770_at_4_0.png

Looks to me like a 4.0 GHz i7-3770!
 
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VR-d is far from irrelevant if you plan to play games using a vm. VT-d allows direct access to hardware using a VM like to the graphics card allowing for much higher FPS etc.
 
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