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 HyperThreading technology. Yes, you read it right. HyperThreading 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 HyperThreading tecnology.

Of course having two real CPUs is far more efficient than using HyperThreading 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.