DC powered tower Computer?

OK, this is a odd issue to say none the less. I have a build in mind for a full size computer that i can run programs for Amateur Radio and other application and possible a portable server. But here's the catch I want to run the whole thing with a 12 V DC power in. now I not sure of the specks just quite yet bet i need a way to make the power out to the components at the correct voltages and the proper pin outs.

Now this can be solved with an inverter and a "off the shelf" Power supply but for me i find that to be the lest efficient way to do solve the problem and I don't what to loses any power due to phantom loads. also a laptop just dosen't have the horsepower to do what I'm planning on doing. plus i think it would be a interesting challenge.

You should also be able to find a 12V DC to DC supply. Computers in cars was quite common, so supplies like this exist, they wont be hardcore gamer type stuff however - that's not something you'd run off a 12V battery.

etc etc, not recommending that product because I'd have no idea, just an example.

12V for the win!

A few interesting things for you here: http://www.mini-box.com/site/index.html

I've used a few PicPSU and they've always worked very well, still going strong.

For a laptop, you can experiment by just putting 12V into it, maybe it won't charge, but it may run.

If that does not work, just make an adapter.

Also, these things make nice phone charger ports too

(Connect it to a DC barrel socket and you have something to charge with from any 12 or 24V supplies, I use PSUs from network equipment)

and just because it came to mind, I like these too:

(the last one is good for getting high voltage from a power bank, micro usb is input)

You could use a thin mini-itx motherboard which is directly powered by DC, such as this:

It uses socket 1150 and should work with most Haswell CPUs and supports DDR3 1600 SO-DIMMs. it can also power SATA devices directly from the motherboard and can also use mSATA. Using this removes the need to get a DC power converter but obviously has it's limitations such as not using able to use most PCIe devices like graphics card and such.