What do I need to run LinuxCNC???

[Sven]

Do not just go ahead with buying new parts to use for LinC without knowing they are fit for purpose.

The single most important thing to run LinC well is the so called latency, for which a test is included with the Linux cnc live cd.

I sort of collect older pc's and test them for this. If the numbers are good, then I keep it.

I now run a pentium 4 2ghz I bought new maybe in 2005 or something.
Ram, ssd and that modern stuff is pretty much irrelevant for the cnc part, but it may be nice for smooth operation for the operator.

With modern boards latency can vary a lot so if you can not test it, or know from others latency is good, do not buy it.

When I started I ran LinC directly from the parallel port.
When I added a 4th axis that did not work so I had to add a BOB.

Once you have the pc, you can just try to run it, if it does not work well, add bob, or add mesa.