best motherboard cpu combo

I am having computer problems,if you were building computer just for Linux cnc ,what components would you use?
As in motherboard, CPU , graphics card etc.

"best" depends on usage and expectations

Are you using software step generation? If so you need a MB parallel port or PCI/PCIE slot
for a added parallel port card. Also for software step generation, you want quite low latency

Do you need a fanless system? (the old Atom D525s and the like had decent latency and are are mostly fanless)
The newer J1800 J1900 MBs are fanless and have acceptable latency with RTAI, though typically not as good
as the older Atoms. The required latency depends on what maximum step rate is required.

Most on card (and in CPU) video is fine now

Are you doing other work on the computer so speed is an issue? If so you may want a G32XX CPU and a H81 or H97 based MB. These need fans but are 2 to 3 x as fast as the typical fanless CPUs (J1800,J1900,N30xx etc) and have quite good latency

Thanks for the input. Yes I need parallel port ,biggest issue is latency, shop computer is pretty much dedicated to my cnc.

Are there any current recommendations on MB/CPU?

I'm doing a lathe retrofit with Mesa PCI-x and servos and would like something with relatively low latency (<50000 ns) for LinuxCNC use only, with no other speed requirements. MB factor is not an issue and fanless CPU is not a requirement but would be a plus.

Keeping MB/CPU/RAM costs low (<$200) would also be a big plus.