Intel has a wide variety of CPUs (Central Processing Units) in its past and present lineup, and it produced several flavors of the Pentium before its general transition to the "Core" technology. The Pentium D and Pentium 4 (P4) are two such examples.
Pentium 4 Origins
The P4 was introduced in November 2000. Its core clock started at 1.3 gigahertz (GHz), it had a 400 megahertz front-side bus and in theory could go all the way to 10 GHz before heat generation became unmanageable.
Pentium D Origins
The Pentium D, meanwhile, did not appear until 2005. In the intervening years, Intel had developed some substantially advanced architecture, such as multiple processing cores on a single CPU chip and support for 64-bit instructions (the Pentium 4 could only handle up to 32-bit instructions).
Dual-Core Pentiums
The "D" does not stand for "Dual Core." Instead, Intel developed a "Pentium Dual Core" that was based on their later "Core" technology, which was distinguished by much lower power requirements and heat generation.
Compatibility
Since the Pentium D and Pentium 4 are very different internally, the D variety is not compatible with older Pentium 4 motherboards, such as the Socket 428 and 478. But the "LGA 775" Pentium 4 is compatible with Pentium D motherboards.
Performance and Price
Since the Pentium D has two processing cores, it is capable of faster performance, but only when the software is designed to recognize and take advantage of multiple cores. Accordingly, Pentium D CPUs cost substantially more, assuming you can find one for purchase.
Tags: compatible with, Core technology, Dual Core, heat generation, Intel developed, Pentium motherboards