HD here means hard disk.
I am a complete beginner at messing around inside computers. But I have a computer with a hard disk with Windows XP installed on it. It uses an Intel Celeron Single-Core Processor. I have another PC that I want to put this HD into which uses an Intelsingle core Pentium III. (yes these are old computers)
Assuming both motherboards have the same ports (is that the right word?) for the hard disk, is it a simple process to take out the hard disk from PC A, plop it into PC B, start up and run?