Core 2 Duo E6700 and Core 2 Extreme X6800

Introduction
Core 2 is the new desktop CPU family from Intel, based on the new Core microarchitecture. For desktops Core 2 comes in two flavors: Core 2 Duo, which replaces Pentium D, and Core 2 Extreme, which replaces Pentium Extreme Edition. Core 2 desktop version was formerly known as Conroe and in this review we will check the performance of two models, Core 2 Duo E6700, which runs at 2.66 GHz, and Core 2 Extreme X6800, which runs at 2.93 GHz. We will compare them to the most high-end CPUs from AMD to date, including Athlon 64 X2 5000+ and Athlon 64 FX-62. Who has the fastest desktop CPU, Intel or AMD? Read on.
Attention: This review has some innacurate results, please read our most recent review for more accurate results.
Pay attention to not confuse Core 2 Duo with Core Duo. Core Duo is the commercial name for a Pentium M manufactured using 65 nm process, codenamed Yonah, while Core 2 Duo is the commercial name for the CPU codenamed Merom (for laptops) or Conroe (for desktops), which uses the new Intel Core microarchitecture.
You can check the CPUs Intel sent us on Figures 1 and 2. Since they were engineering samples, they didn’t have their final markings on them. Instead they had an “Intel Confidential” marking. On Figure 2 you can see their bottom side. They use the standard socket 775 used by current Pentium 4 and Pentium D CPUs, the only difference you can see is the number and location of the capacitors found in the middle. We added our Pentium 4 550 (3.4 GHz) on the photo so you can see this.
click to enlargeFigure 1: Core 2 Extreme X6800 and Core 2 Duo E6700 engineering samples.
click to enlargeFigure 2: Core 2 Extreme X6800, Core 2 Duo E6700 and Pentium 4 550 (3.4 GHz).
Keep using socket 775 was a great move from Intel. Socket 775 motherboards launched before Core 2 CPUs were available may be compatible with them. There are two requirements: first, the motherboard must be capable of supplying the voltage required by the new CPU; and second, the motherboard must be capable of supplying the external clock rate (FSB) required by the new CPU. Unfortunately only newer motherboards are capable of supplying the voltage required by Core 2 CPUs.
Internally, however, Core 2 CPUs have nothing to do with Pentium 4 or Pentium D. While Pentium 4 and Pentium D are based on Intel’s 7th generation microarchitecture – also known as NetBurst – Core 2 is based on a new architecture, called Core, which is based on Pentium M’s (which is based on Pentium III’s - as you will see on next page, Core 2 CPUs report their Family ID as being "6", the same one as Pentium Pro, Pentium II and Pentium III). Please read our Inside Intel Core Microarchitecture tutorial to learn everything you need to know about this new architecture.
Since they use a totally different internal architecture, you cannot compare clock rates used by Core 2 CPUs with the ones used by other CPUs like Pentium 4 or Pentium D. Core 2 CPUs may be faster using a lower clock rate as they internally process things differently. In fact, we will check this aspect on our review. Here is a problem for the Average Joe. Even though Intel started identifying their CPUs by model numbers a while ago, people still tend to compare CPUs by their clock rates. It will be hard for us to say to which previous Intel CPU or to which AMD CPU each Core 2 model is comparable by just looking to their specs.
Let’s now take a closer look on Core 2 technical specs.

The main specs of the reviewed Core 2 CPUs include:
Core microarchitecture
Dual-core technology
1,066 MHz external clock rate (266 MHz x 4)
4 MB unified L2 memory cache
Intel Virtualization Technology
Execute Disable Bit
Intel EM64T Technology
Intelligent Power Capability
Some things pop right on our face. The first one is the total lack of HyperThreading technology, which seems to be an exclusive feature of Pentium 4 and Pentium Extreme Edition CPUs. This technology emulates two CPUs per core, so a compatible operating system like Windows XP or Linux would recognize a standard Pentium 4 as two CPUs and a Pentium Extreme Edition as four CPUs (two per core) – Pentium D also lacks this feature. If Intel will add this feature back on Core 2 family is still a mystery.
The second thing is the amazing amount of L2 memory cache present on the reviewed models (keep in mind that Intel will probably release models using less memory cache). Intel decided to use a unified L2 cache, contrasted to a per-core approach like Pentium D, Pentium Extreme Edition, Athlon 64 X2 and dual-core Athlon 64 FX. According to Intel their approach provides a higher performance, as each core can use data that is already on the unified cache but was loaded from the main memory by the other core. Also, the cores can negotiate how much memory cache each one will use at a given moment. The division between them doesn’t need to be 50%-50%. At a given moment one core may be using 75% of the memory cache and the other one, 25%. On the separated approach the division is always 50%-50%, meaning that one core can have unused cache at the same time that the other core has ran out of cache, and this core cannot simply “borrow” memory cache from the other core like on the unified approach. As for the external bus, Core 2 family keeps using the same idea that was introduced with the very first Pentium 4 CPU: quad data rate (QDR), i.e. the CPU transfers externally four data per clock cycle. Because of this the CPU external clock rate is said to be four times its actual clock rate. These Core 2 CPUs, for example, have an external bus of 266 MHz but transferring four data per clock cycle, thus Intel label their external bus as being of 1,066 MHz.
So Core 2 Duo E6700 achieves its 2.66 GHz internal clock rate by multiplying its 266 MHz external clock rate by 10 and Core 2 Extreme X6800 achieves its 2.93 GHz internal clock rate by multiplying its 266 MHz clock rate by 11.
These CPUs also incorporates dual-core technology, meaning that internally they have two complete CPUs. SMP-compatible operating systems like Windows XP and Linux will recognize two CPUs. SMP stands for Symmetric Multi Processing and is the ability of a system to use more than one CPU.
On Figures 3 and 4 you see CPU ID results taken with CPU-Z for the reviewed CPUs. As you can see, they report as being “Family 6”, i.e. Intel 6th generation, the same family as Pentium Pro, Pentium II, Pentium III and Pentium M. It is really funny to see a new CPU family with a CPU ID Family ID lower than the previous family (Pentium 4 and Pentium D reports Family ID as 7). The clock rates are being erroneously reported as 1,6 GHz due to Enhanced SpeedStep Technology.
Figure 3: Core 2 Duo E6700.
Figure 4: Core 2 Extreme X6800.
Intelligent Power Capability is an enhancement over Enhanced SpeedStep Technology that we have explained in details in our Inside Intel Core Microarchitecture tutorial.

We summarized below all CPUs included in this review with their main specs.
CPU
Cores
Internal Clock
External Clock
L2 Memory Cache
Platform
TDP
Athlon 64 3800+
1
2.4 GHz
*
512 KB
Socket 939 (DDR)
89 W
Athlon 64 X2 4600+
2
2.4 GHz
*
512 KB x 2
Socket 939 (DDR)
110 W
Athlon 64 X2 5000+
2
2.6 GHz
*
512 KB x 2
Socket AM2 (DDR2)
89 W
Athlon 64 FX-60
2
2.6 GHz
*
1 MB x 2
Socket 939 (DDR)
110 W
Athlon 64 FX-62
2
2.8 GHz
*
1 MB x 2
Socket AM2 (DDR2)
125 W
Pentium 4 550
1
3.4 GHz
800 MHz (200 MHz x 4)
1 MB
Socket 775 (DDR2)
115 W
Core 2 Duo E6700
2
2.66 GHz
1,066 MHz (266 MHz x 4)
4 MB
Socket 775 (DDR2)
65 W
Core 2 Extreme X6800
2
2.93 GHz
1,066 MHz (266 MHz x 4)
4 MB
Socket 775 (DDR2)
75 W
* Since AMD64 CPUs have their memory controller embedded in the CPU, the datapath between the CPU and the memory controller uses the CPU internal clock rate instead of an external clock rate as it happens on Intel CPUs. To communicate with components outside the CPU, AMD64 CPUs have two busses, the memory bus and the HyperTransport bus. The memory bus run up to DDR400 or DDR2-800 depending on the platform (socket 939 or socket AM2, respectively) and the HyperTransport bus of the listed CPUs works at 1,000 MHz transferring two 16-bit data per clock cycle (also labeled as “2,000 MHz”), achieving a 4,000 MB/s transfer rate on each direction. A 800 MHz external bus on Intel CPUs can provide a maximum theoretical transfer rate of 6,400 MB/s while a 1,066 MHz external bus can provide up to 8,528 MB/s. Direct comparison of this particular spec between Intel and AMD CPUs is really tricky as Intel external bus is used for both accessing the main RAM memory and other components – the video card in particular –, while on AMD64 CPUs two separated paths are used. Also, on Intel CPUs the same datapath is used for transferring data in and out, while HyperTransport bus provides two separated paths for input and output.
Thanks to Core microarchitecture –an enhancement over Pentium M’s – Core 2 family dissipates a lot less power, meaning less heat (TDP stands for Thermal Design Power). As you can see on the table above, Core 2 Duo and Core 2 Extreme dissipate less power than all other CPUs included in our review. It is amazing to see how a dual-core CPU, which has two complete CPUs inside, can dissipate less power than a single-core Pentium 4. You can claim that they run at lower clock rates, however keep in mind that they have four times the amount of memory cache found on Pentium 4, which by itself would increase the CPU power dissipation a lot.
Unfortunately Intel didn’t provide us Pentium D and Pentium Extreme Edition samples for reviewing.