The main specs of the reviewed Core 2 CPUs include:
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.
To learn more about the other features listed above, just click on the links provided to read our tutorials on them.
Another very important difference between Core 2 and Pentium 4 families is the amount of dissipated power. We will talk more about this on next page.
