Intel's Core i7 870 & i5 750, Lynnfield: Harder, Better, Faster Stronger
by Anand Lal Shimpi on September 8, 2009 12:00 AM EST- Posted in
- CPUs
Overclocking Lynnfield at Stock Voltage: We're PCIe Limited
Remember the on-die PCIe controller? Yep. It's to blame.
Lynnfield is Intel's first attempt at an on-die PCIe controller and it actually works surprisingly well. There are no performance or compatibility issues.
The on-die PCIe controller needs more voltage as you overclock Lynnfield, limiting Lynnfield's stock vt overclocking potential.
Unfortunately the PCIe controller on Lynnfield is tied to the BCLK. Increase the BCLK to overclock your CPU and you're also increasing the PCIe controller frequency. This doesn't play well with most PCIe cards, so the first rule of thumb is to try and stay at 133MHz multiples when increasing your BCLK.
The second issue is the bigger one. As you increase the BCLK you increase the frequency of the transistors that communicate to the GPU(s) on the PCIe bus. Those transistors have to send data very far (relatively speaking) and very quickly. When you overclock, you're asking even more of them.
We know that Bloomfield can easily hit higher frequencies without increasing the core voltage, so there's no reason to assume that Lynnfield's core cannot (in fact, we know it can). The issue is the PCIe controller; at higher frequencies those "outside facing" transistors need more juice to operate. Unfortunately on Lynnfield rev 1 there doesn't appear to be a way to selectively give the PCIe transistors more voltage, instead you have to up the voltage to the entire processor.
Intel knows the solution to Lynnfield's voltage requirement for overclocking, unfortunately it's not something that can be applied retroactively. Intel could decouple the PCIe controller from BCLK by introducing more PLLs into the chip or, alternatively, tweak the transistors used for the PCIe interface. Either way we can expect this to change in some later rev of the processor. Whether that means we'll see it in the 45nm generation or we'll have to wait until 32nm remains to be seen.
The good news is that Lynnfield can still overclock well. The bad news is that unlike Bloomfield (and Phenom II) you can't just leave the Vcore untouched to get serious increases in frequency.
Facebook
Twitter
RSS
343 Comments
View All Comments
moronsworld - Saturday, September 26, 2009 - link
To all you morons that don't understand economics. amd gone = intel monopoly = intel processors overpriced. Plain and simple. Take an economy class or 2, you morons. AMD is a good company, just that Intel's processors are better at the moment. God too many morons in this world that are allowed to vote. We live in a society ruled by morons.TA152H - Tuesday, September 8, 2009 - link
Actually, you don't really know what you're talking about.On-die memory controllers are nothing new. The Nexgen 586 had it in the mid-90s. Intel just knew when to add it, and when not to. That's why the Core 2 blows AMD processors away, while being significantly smaller.
AMD instruction schedulers were behind Intel's Pentium Pro from 1995 until the Phenom II came out. It still doesn't have full memory disambiguation like Intel introduced with the Core 2, but at least the memory scheduling is now on par with the Pentium Pro. I'm not sure that something they like brought up though.
64-bit processing is also old hat, and really was just an extension of the 386 protected mode anyway, with a lot of Microsoft input.
The K8 wasn't really much of an architecture, it was a K7 with a memory controller, and a couple of extra stages for better IPC, that most idiots thought was for higher clock speeds. It was a failure, and was what put AMD in the situation where they are now. It was, generally, better than the Netburst, but then, is that such a high bar to get over? The problem was, they actually believed it was a good processor until the Core 2 relieved them of that misapprehension. The reality is, Intel's mobile chips were always better than the K8, but the damn fools made us buy the Pentium 4 for the desktop. To AMD's credit, at least they never made anything horrible like that, but, really, their primary claim to fame was based more on the terrible Intel design than a great processor of their own, and the fact Intel wouldn't let us use the mobile chips for desktops.
JonnyDough - Tuesday, September 8, 2009 - link
Please work on your English before replying to me in the future. Thanks.Aenslead - Tuesday, September 8, 2009 - link
So you *must* have perfect english to reply in these forums?Gosh, never saw that in the Terms and Conditions agreement when I created my account. So that means that anybody (or a nobody, like you) have a say on what other races and people from other countries that don't speak English as their first language, that LIKE READING and giving their opinion in a FREE MOFO OPEN FORUM, must do to post here?
You and your kind are pathetic.
JonnyDough - Tuesday, September 8, 2009 - link
I didn't say anything about having perfect English. You sir, are a troll. I just wanted his reply to be coherent. This is the ENGLISH version of DailyTech, there are other language versions. His post didn't even make sense, and yours was just trolling.ginbong - Wednesday, September 9, 2009 - link
I understood what he said, maybe you need to sharpen up your analytical skills and stop being a dlckhead on this hardware analysis website.Better yet, how about taking the money you have saved for your next PC upgrade and enrolling into Grade 1 again.
dastruch - Tuesday, September 8, 2009 - link
and you don't get it too... patheticjigglywiggly - Tuesday, September 8, 2009 - link
This is a hot cpu, except I want 6 cores + HT. 32nm... quads ahh yeah. I still don't like the i5, because I don't want two sockets on one brand at the same time. It just limits options, I am only looking at i7/i9, because I bought this qx6700 in 2006 for 1000$. It was a good purchase, because q6600s were a while away and they were 500$. I got my qx6700 to 3.85ghz, now it's at 3.5ghz stable. Curse you electromigration! Also curse you economy! I don't have enough money for a 6core+6HT 1000$ cpu again.JonnyDough - Tuesday, September 8, 2009 - link
*Laughs at the moron...Go buy a Ferrari and then wreck it and sell it for parts. That's essentially a larger scale version of what you did.
Lifted - Tuesday, September 8, 2009 - link
Huh? Buying a $1000 CPU is like wrecking a Ferrari?"Laughs at the moron"