Ten Year Anniversary of Core 2 Duo and Conroe: Moore’s Law is Dead, Long Live Moore’s Law
by Ian Cutress on July 27, 2016 10:30 AM EST- Posted in
- CPUs
- Intel
- Core 2 Duo
- Conroe
- ITRS
- Nostalgia
- Time To Upgrade
Core: It’s all in the Prefetch
In a simple CPU design, instructions are decoded in the core and data is fetched from the caches. In a perfect world, such as the Mill architecture, the data and instructions are ready to go in the lowest level cache at all times. This allows for the lowest latency and removes a potential bottleneck. Real life is not that rosy, and it all comes down to how the core can predict what data it needs and has enough time to drag it down to the lowest level of cache it can before it is needed. Ideally it needs to predict the correct data, and not interfere with memory sensitive programs. This is Prefetch.
The Core microarchitecture added multiple prefetchers in the design, as well as improving the prefetch algorithms, to something not seen before on a consumer core. For each core there are two data and one instruction prefetchers, plus another couple for the L2 cache. That’s a total of eight for a dual core CPU, with instructions not to interfere with ‘on-demand’ bandwidth from running software.
One other element to the prefetch is tag lookup for cache indexing. Data prefetchers do this, as well as running software, so in order to avoid a higher latency for the running program, the data prefetch uses the store port to do this. As a general rule (at least at the time), loads happen twice as often as stores, meaning that the store port is generally more ‘free’ to be used for tag lookup by the prefetchers. Stores aren’t critical for most performance metrics, unless the system can’t process stores quickly enough that it backs up the pipeline, but in most cases the rest of the core will be doing things regardless. The cache/memory sub-system is in control for committing the store through the caches, so as long as this happens eventually the process works out.
Core: More Cache Please
Without having access to a low latency data and instruction store, having a fast core is almost worthless. The most expensive SRAMs sit closest to the execution ports, but are also the smallest due to physical design limitations. As a result, we get a nested cache system where the data you need should be in the lowest level possible, and accesses to higher levels of cache are slightly further away. Any time spent waiting for data to complete a CPU instruction is time lost without an appropriate way of dealing with this, so large fast caches are ideal. The Core design, over the previous Netburst family but also over AMD’s K8 ‘Hammer’ microarchitecture, tried to swat a fly with a Buick.
Core gave a 4 MB Level 2 cache between two cores, with a 12-14 cycle access time. This allows each core to use more than 2MB of L2 if needed, something Presler did not allow. Each core also has a 3-cycle 32KB instruction + 32KB data cache, compared to the super small Netburst, and also supports 256 entries in the L1 data TLB, compared to 8. Both the L1 and L2 are accessible by a 256-bit interface, giving good bandwidth to the core.
Note that AMD’s K8 still has a few advantages over Core. The 2-way 64KB L1 caches on AMD’s K8 have a slightly better hit rate to the 8-way 32KB L1 caches on Core, with a similar latency. AMD’s K8 also used an on-die memory controller, lowering memory latency significantly, despite the faster FSB of Intel Core (relative to Netburst) giving a lower latency to Core. As stated in our microarchitecture overview at the time, Athlon 64 X2s memory advantage had gotten smaller, but a key element to the story is that these advantages were negated by other memory sub-system metrics, such as prefetching. Measured by ScienceMark, the Core microarchitecture’s L1 cache delivers 2x bandwidth, and the L2 cache is about 2.5x faster, than the Athlon one.
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Icehawk - Wednesday, July 27, 2016 - link
I replaced my C2D a couple of years ago only because it needed yet another mobo and PSU and I do like shiny things, I'd bet if it was still around I could pop in my old 660GTX and run most games just fine at 1080. At work there are some C2Ds still kicking around... and a P4 w XP! Of course a lot of larger businesses have legacy gear & apps but it made me chuckle when I saw the P4.With the plateau in needed performance on the average desktop there just isn't much reason to upgrade these days other than video card if you are a gamer. Same thing with phones and tablets - why aren't iPads selling? Everyone got one and doesn't see a need to upgrade! My wife has an original iPad and it works just fine for what she uses it for so why spend $600 on a new one?
zepi - Wednesday, July 27, 2016 - link
You are not mentioning FPGA's and non-volatile memory revolution which could very well be coming soon (not just flash, but x-point and other similar stuff).Personally I see FPGAs as a clear use for all the transistors we might want to give them.
Program stuff, let it run through a compiler-profiler and let it's adaptive cloud trained AI create an optimal "core" for your most performance intensive code. This recipe is then baked together with the executable, which will get programmed near-realtime to the FPGA portion of the SOC you are using. Only to be reprogrammed when you "alt-tab" to another program.
Obviously we'll still need massively parallel "GPU" portion in chip, ASIC-blocks for H265 encode / decode with 8K 120Hz HDR support, encryption / decryption + other similar ASIC usages and 2-6 "XYZlake" CPU's. Rest of the chip will be FPGA with ever more intelligent libraries + compilers + profilers used to determine at software compile time the optimal recipe for the FPGA programming.
Not to mention the paradigm chances that non-volatile fast memory (x-point and future competitors) could bring.
wumpus - Thursday, August 4, 2016 - link
FPGAs are old hat. Granted, it might be nice if they could replace maybe half of their 6T SRAM waste (probably routing definitions, although they might get away with 4T), but certainly the look-up needs to be 6T SRAM. I'd claim that the non-volitile revolution happened in FPGAs (mainly off chip) at least 10 years ago.But at least they can take advantage of the new processes. So don't count them out.
lakerssuperman - Wednesday, July 27, 2016 - link
I'm reading this from my old Sony laptop with a Core 2 Duo and Nvidia GPU in it. With an SSD added in, the basic task performance is virtually indistinguishable from my other computers with much newer and more powerful CPU's. Granted it can get loud when under load, but the Core 2 era was still a ways away from the new mobile focused Intel we have now.I guess my basic point is that I got this laptop in 2009 and for regular browsing tasks etc, it is still more than adequate which is a testament to both the quality and longevity of the Core 2 family, but where we are with CPU power in general. Good stuff.
jeffry - Monday, August 1, 2016 - link
I agree. Got me a Sony SZ1m in 2007 (i think?), flip switched the core duo yonah with a core2duo T7200 merom. Because its 64 bit and now i can run 64 bit os and 64 bit software on it.boozed - Wednesday, July 27, 2016 - link
Funny to think that despite four process shrinks, there's been minimal power and clock improvement since then.UtilityMax - Wednesday, July 27, 2016 - link
To some of you it may sound like a surprise, but a Core2Duo desktop can still be fairly usable as a media consumption device running Windows 10. I am friends with a couple who are financially struggling graduate students. The other way, they brought an ancient Gateway PC with LCD from work, and they were wondering if they could rebuild it into a PC for their kid. The specs were 2GB of memory and Pentium E2180 CPU. I found inside of a box of ancient computer parts which I never throw away an old Radeon graphics card and a 802.11n USB adapter. I told them to buy a Core2Duo E4500 processor online because it cost just E4500. After installing Windows 10, the PC runs fairly smoothly. Good enough for web browsing and video streaming. I could even load some older games like Quake 3 and UrbanTerror 4.2 and play them with no glitch.UtilityMax - Wednesday, July 27, 2016 - link
I mean, the E4500 cost just 5 bucks..DonMiguel85 - Wednesday, July 27, 2016 - link
Still using a Core 2 Quad 9550. It bottlenecks most modern games with my GTX 960, but can still run DOOM at 60FPS.metayoshi - Wednesday, July 27, 2016 - link
Wow. Actually, just last holiday season, I replaced my parents' old P4 system (with 512 MB RAM! and 250 GB SATA Maxtor HDD!) with my old Core i7-860 since I upgraded to a system with a Core i7-4790K that I got on a black friday sale. The old 860 could definitely still run well for everyday tasks and even gaming, so it was more than good enough for my parents, but the video processing capabilities of the more recent chips are a lot better, which is the main reason I updated. Also, the single threaded performance was amazing for the 4790K, and the Dolphin emulator did not run so well on my 860, so there was that.Speaking of Core 2, though, I owned an ASUS UL30Vt with the Core 2 Duo SU7300 CPU and an Nvidia GeForce G 210M. While the weak GPU was not so great for high end gaming, the overall laptop was amazing. It was more than powerful enough for everyday tasks, and had amazing battery life. It was pretty much what every ultrabook today desires to be: sleek, slim, but powerful enough with great battery life. That laptop to me was the highlight of the Core 2 era. I was kind of sad to let it go when I upgraded to a more powerful laptop with an Ivy Bridge CPU and 640M LE GPU. I don't think any laptop I owned gave me as much satisfaction as that old Asus. Good times.