Thresholds in computing: Part 10 – Beyond Thin-ITX

(Part 10 in a series of posts on small-form-factor computing)

In my previous posts on Thin-ITX, I made two complaints:

  1. There is still some cabling required in Thin-ITX, to connect the front panel ports (USB, audio) and power button to the motherboard.
  2. A Thin-ITX system can still be further shrunk, since nothing really limits it to a minimum size of 17×17cm.
  3. There are still more sources of heat than are really required for a Thin-ITX system
    The first two issues have been resolved by another (unofficial) form factor: Intel’s Next Unit of Computing (NUC). The NUCs are barebones small-form-factor systems—just add CPU, RAM, SSD, and water—with motherboards measuring 10×10cm. They carry the full range of connectivity (USB, audio, HDMI/Displayport) enjoyed by most PCs, although perhaps not the full complement.

nuc-hand-ports1

These things are deliciously small. In fact,at  12×11×3.5cm, they are barely larger than the motherboards they house. This is an approach to cabling elimination that we’ve seen before in ITX: If you can’t bring the board closer to the sides, bring the sides closer to the board.

Intel NUC: peripheral side
Intel NUC: peripheral side

The third issue I mentioned above—sources of heat—is also alleviated somewhat. The CPU and PCH are on one side of the board, cooled by the same cooler. The rest of the (heat-producing) components are on the other side.

Intel NUC: CPU side (without cooler)
Intel NUC: CPU side (without cooler)

The disadvantage: The Intel NUC units are limited to a TDP of 17W only, to maintain its low height.

Enter third-party solutions: The Gigabyte BRIX Pro and Zotac ZBox. Intel doesn’t seem to have an official NUC specification published yet, but that has not stopped third-party manufacturers from coming up with passively cooled NUC cases or systems that share the same dimensions.

Gigabyte BRIX Pro – BXi7-4770R
Gigabyte BRIX Pro – BXi7-4770R

The Gigabyte BRIX Pro is a taller NUC-like unit that comes with CPU options up to an i7-4770R (65W). Aside from the higher TDP, the 4770R also comes with Intel Iris Pro graphics, which came close to mid-range gaming laptop graphics performance in a number of review benchmarks.

ZOTAC ZBOX – ID89 Plus
ZOTAC ZBOX – ID89 Plus

The ZOTAC ZBOX is a wider mini-PC (36×27×9.5cm) with CPU options up to i5-3470T (35W). This one has the regular flavour of integrated graphics.

Why couldn’t Intel just have extended the ITX spec to allow for smaller motherboards? What changes were required to enable these tiny yet performant machines?

The ITX CPU socket #

Thin-ITX systems still use the regular LGA socket used by their ITX, and even their larger micro-ATX/ATX brethren.

ASUS Q87T, with CPU socket in lower right
ASUS Q87T, with CPU socket in lower right

Once you put a heatsink over the CPU, it’s hard to escape the observation that the CPU socket is fully a quarter of the motherboard’s footprint. Why does the CPU socket need to be so large? And much of it is not even being used for component mounting.

When you look at some of the downright crazy cooling towers used by overclocking enthusiasts, it’s easy to appreciate why stable mounting is required. These things are huge. And heavy. And in most systems the board is mounted vertically, which means these things could easily rip out a smaller socket with the kind of bending forces they exert.

ASUS P8Z77-I Deluxe with GTX680 [tonymacx86]
ASUS P8Z77-I Deluxe with GTX680 [tonymacx86]

So as long as you’re designing a board that could conceivably be used for overclocking, you want to be able to accommodate such coolers. Even if they look ridiculous on little ITX boards. But it would be even more ridiculous to move the same hardware to ATX form factor just to make it look less silly. Remember, mini-ITX is about removing unnecessary things, not about reducing performance.

Thin-ITX does not use a 24-pin motherboard cable or the 4-pin ATX12V—it takes in 19V via a DC jack or 2-pin onboard connector, and is limited to 65W TDP CPUs. Simply put, you’re not going to be pumping a lot of power through a Thin-ITX system.

You are never going to need these cooling behemoths with Thin-ITX systems.

Thin-ITX boards stuck with the ITX specifications anyway, because you want new products to be compatible with other PC parts that are out there, and that means using an existing socket design—in the case of Intel’s 4th-generation Core processors, that’s LGA1150. And that also means a quarter of your motherboard’s footprint taken up by the LGA1150 socket.

What happens if we try to shrink the motherboard to 10×10cm and still use a LGA1150 socket? A 10×10cm board has a footprint 65% smaller than mini-ITX. That means the CPU socket will take up almost 70% of the board’s footprint!

Clearly that’s a waste of space. We’ve hit another threshold in small-form-factor computing, and it’s time to drop what we don’t need. Intel’s LGA1150 socket guide has engineering drawings that put the hole-to-hole measurements of the socket at 7.5cm. How much can we save from that?

The NUC CPU socket #

Intel DC33217GKE NUC board
Intel DC33217GKE NUC board

I can’t find any engineering diagrams for the NUC socket, but estimating it from motherboard photos and knowing that the board is 10×10cm, we can judge the hole-to-hole measurement to be about 3cm. Also note that there are only 3 mounting holes rather than 4—with a horizontally mounted board, we simply don’t need the kind of stability provided by a 4-mounting-hole socket. The NUC’s socket area is less than 16% the footprint of the LGA1150 socket!

This does not mean that the CPU cooling fan needs to be tiny as well. We can well see from teardown images that the fan still covers a significant area of the board. But what matters here is that the motherboard has more PCB space for other components, instead of setting it aside for the CPU socket. Removing the swappable CPU socket (i.e. going from LGA to BGA) removes the mechanical portion of the socket, freeing up even more area.

And that, in a nutshell, is how we move past Thin-ITX, beyond the confines of the ATX/ITX specification, and squeeze a 65W quad-core system into 10×10cm.


I am pretty much at the end of my small-form-factor writing streak here, and will no longer be posting semi-regular updates. But if you are interested in the topic, do drop me an email, or look me up on G+/Hangouts.

See also Thresholds in computing: Part 9 – heat dissipation and Thin-ITX