Die Size / Package / Socket
Here you see a die size comparison of Pentium 4, Pentium III, Athlon and Duron. The 217 mm² of Pentium 4 are more than double the size of Pentium III and almost double the size of Athlon. This seems rather surprising when you realize that Pentium 4 has got 42 million transistors and Athlon 37 million. Each of the four is manufactured in 0.18µ-process. Bottom line: Pentium 4 is big!
Intel has reacted to the complaints about damaged flip chips of Pentium III and Celeron. The recent flip chip package of the two processors exposes the die to direct forces from outside. A badly mounted heat sink can easily damage the sensitive silicon and destroy the processor. Intel equipped Pentium 4 with a protective metal cover that saves the die from any damage.
Pentium 4's package and Socket is a bit larger than Pentium III's, but the difference isn't much. When you see a Pentium 4 on its own you mistakenly estimate it's of the same size as a Pentium III.
This is the new Socket423. As you never would have guessed it comes with 423-pins, thus 53 pins more than Pentium 3. The majority of those new pins are required to supply Pentium 4 with the vast amount of power it requires.