Just for the hell of it, here are Intel's max numbers for old "Williamette" P4 (w/ .18um aluminum) that was recently replaced:
1.4 2.1V 55.3W
1.5 2.1V 57.9W
1.6 2.1V 60.8W
1.7 2.1V 63.5W
1.8 2.1V 66.1W
1.9 2.1V 72.8W
2.0 2.1V 75.3W
And here are Intel's max numbers for the new "Northwood" P4" (w/ .13um copper):
1.8A 1.5V 49.7W
2.0A 1.5V 52.4W
2.2A 1.5V 55.1W
2.4A 1.5V 57.8W (projected)
2.6A 1.5V 60.5W (projected)
2.8A 1.5V 63.2W (projected)
3.0A 1.5V 66.0W (projected)
3.4A 1.5V 71.5W (projected)
From these numbers, it's quite obvious how the P4 is able to overclock so well. Even at 3.4GHz, the new P4 still produces less heat than the old "Williamette" P4 at 2.0GHz. Clearly, Intel experienced some benefit from the improved processor layout, the copper interconnects (used by AMD after 900MHz), and, of course, the .13um interconnects. The new P4 core also has the advantage of a 116mm^2 surface area plus a heat spreader, compared to 80mm^2 and no heat spreader for the Thoroughbred.
1.4 2.1V 55.3W
1.5 2.1V 57.9W
1.6 2.1V 60.8W
1.7 2.1V 63.5W
1.8 2.1V 66.1W
1.9 2.1V 72.8W
2.0 2.1V 75.3W
And here are Intel's max numbers for the new "Northwood" P4" (w/ .13um copper):
1.8A 1.5V 49.7W
2.0A 1.5V 52.4W
2.2A 1.5V 55.1W
2.4A 1.5V 57.8W (projected)
2.6A 1.5V 60.5W (projected)
2.8A 1.5V 63.2W (projected)
3.0A 1.5V 66.0W (projected)
3.4A 1.5V 71.5W (projected)
From these numbers, it's quite obvious how the P4 is able to overclock so well. Even at 3.4GHz, the new P4 still produces less heat than the old "Williamette" P4 at 2.0GHz. Clearly, Intel experienced some benefit from the improved processor layout, the copper interconnects (used by AMD after 900MHz), and, of course, the .13um interconnects. The new P4 core also has the advantage of a 116mm^2 surface area plus a heat spreader, compared to 80mm^2 and no heat spreader for the Thoroughbred.