Simply put, Pentium D is a Pentium 4 with dual-core technology. But there is a very important difference between Pentium 4 and Pentium D besides this new technology. The new Pentium D doesn't have Hyper-Threading technology. Yes, you read it right. Hyper-Threading makes the operating system to think that there are two CPUs installed on the system. Thus, when you use a Pentium 4 with this technology, Windows XP recognizes it as if two CPUs were installed on the system. Read our tutorial about this subject.

So, when you use a Pentium D, the operating system will recognize two CPUs, and not four as it would happen if this new processor had Hyper-Threading tecnology.

Of course having two real CPUs is far more efficient than using Hyper-Threading technology, which is just an emulation of having two CPUs on the system, using idle parts of the CPU to perform this emulation.

Three Pentium D models were announced:

• Pentium D 820: 2.8 GHz, 1 MB L2 memory cache for each core
• Pentium D 830: 3.0 GHz, 1 MB L2 memory cache for each core
• Pentium D 840: 3.2 GHz, 1 MB L2 memory cache for each core

All of them use a 800 MHz external bus and use the Intel 64-bit extensions (EM64T), so they are based on Pentium 4 6xx series.