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Well then, rather than inquiring as to how to blink an LED with a Pentium IV, you first task would be designing a motherboard from the ground up.
A truly complex and arduous task indeed, one which I do not believe you have fully come to grips with its complexity.
On the other hand, if you are set on blinking an LED with x86 architecture by designing and constructing a functional circuit from the chip up, you would be far better off finding an Intel 8086 and start from there. It would still require some time an effort finding the necessary parts and assembling a minimal circuit, but is is certainly doable.
Or you if are in the mood for a bit more of a challenge, obtain a Quark SoC X1000 processor of which the Intel Galileo is based and attempt to design and construct a minimal circuit. Intel has plenty of documentation and benchmark designs available for just such a challenge.
However, designing a functional motherboard for a Pentium IV, with memory, flash ROM, BIOS, etc., is a lofty goal indeed. As you certainly will not be building it on a breadboard or prototyping board, the PCB design and fabrication skills required alone will probably make your hair turn gray or fall out before its time.
Of course, you could always attempt to wire wrap it. :lol: Sorry, inside joke.
Swimming the English Channel has never been a goal of mine, neither is the challenge of designing and fabricating a Pentium IV class motherboard. :wink:
B.t.w. you didn't tell which Pentium 4 type you have.
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The Pentium 4 system achitecture stands against designing a simple "minimum circuit". You'll need always both support chips to connect e.g. a BIOS flash. You don't need external RAM for a blinking LED application, but the system is still rather unhandy. I don't expect that other Intel or third party chipsets are much better in this regard.
Reviewing the original question, I'm guessing that he wants just to draw the circuit and layout of a flash-LED, being the Pentium4 the PC platform where will run a CAD tool. Seriously speaking, he needs to elaborate more the need.