Thresholds in computing: Part 5 – Steam Machine, ITX done right

(Part 5 in a series of posts on small-form-factor computing)

So I said we were going to shrink the desktop further today. Well, that will have to wait some days longer, since iFixit’s teardown of the Steam Machine beta just arrived in my feeds.

Steam Machine (beta kit) with controller
Steam Machine (beta kit) with controller

The Steam Machine ’s innards follow closely a number of optimisations we have laid down in Parts 2 and 3, and Valve has gone one step further as well—we’ll get to that shortly.

A flat ITX Machine #

Steam Machine (beta kit), with top open
Steam Machine (beta kit), with top open

With the cover off, we see just how snugly everything is packed inside. We have an SFX PSU, a 2.5″ hard drive (with space for another), ITX motherboard (underneath) specced with 16GB of RAM and i5-4570 quad-core, and a high-end graphics card, the GTX780 ($500 at time of writing).

The Steam Machine beta kit (henceforth SMbk) uses a flat layout, similar to what many home entertainment set-tops look like. So far we’ve seen:

  • Tower layouts — The “traditional” desktop, with expansion cards perpendicular to motherboard, PSUs above or below motherboard, storage drives typically near the front of the case.
  • Cube layouts — The SG08. Expansion cards still perpendicular to motherboard, but PSUs and storage drives are shifted around to make the case dimensions more cuboidal.
  • Flat layouts — The SMbk. Everything is laid horizontally, nothing is stacked except for small items like 2.5″ storage drives.

Shrinking the Steam Machine: possible? #

Let’s start our examination of the SMbk by looking at what determines the dimensions of the case. Or in other words, which are the largest components in the case? Which components, if shrunk, will make the case smaller?

Steam Machine (beta kit), top view labelled
Steam Machine (beta kit), top view labelled

Depth-wise (front to back), the graphics card is obviously the limiting factor here. The SMbk is a gaming machine, and needs graphics prowess deserving of one, so this is almost a non-negotiable. The only way to shrink this would be to try to put the same graphics chip on a smaller board (and smaller cooler). Otherwise, the case length can be no smaller than the card’s length, about 27 cm.

Width-wise, we are limited by the motherboard and graphics card widths. The graphics card is able to slot in to the PCIe slot with what is known as a riser card.

PCIe ×16 riser card
PCIe ×16 riser card

This means that the minimum width of the case would be roughly the motherboard width (17 cm) plus graphics card width (standard ~11 cm), subtracting for a little bit of overhang, to give ~27 cm.

Height-wise, the CPU cooler is only 2.7 cm and the SMbk uses low-profile memory (memory sticks with short heat sinks), so in total the motherboard plus CPU cooler would not exceed a height of 4 cm.
Expansion card slots have standard dimensions to follow—~11 cm in width, and no more than ~2 cm in height. High-end graphics cards tend to use up about two slots height-wise, which will use up about 4 cm.
The SFX PSU, covered in Part 3, is about 6.4 cm in height.
This limits the case height to a minimum of ~7 cm, determined by the PSU’s height.

So this is about as compact as we can make the SMbk without making some sacrifices. Well done, Valve.

Could we use a micro-ATX motherboard and ATX PSU? #

What happens if we try to assemble this with a micro-ATX motherboard and an ATX PSU instead?

Width-wise, the SMbk would grow to (24 + 11 – 1 = 34) cm.
Height-wise it would grow to 8 cm.
Depth-wise it would have to accommodate the PSU width of 15 cm, as well as the motherboard depth of 24 cm. We could conceivably reduce this by stacking the PSU above the motherboard, but it must be sufficiently high to not bump the memory sticks, which would mean an increase in height of at least 2 cm …

In short, a SMbk with micro-ATX board and ATX PSU will be significantly larger than the ITX board + SFX PSU version. If we are to keep minimum case dimensions, there simply is no middle ground to be had here.

Shroud-directed cooling #

Another interesting tidbit to note about the SMbk: it has no case fans whatsoever! (Unlike the SG08.) How does the SMbk take care of case cooling without any case fans?

In Part 3, we touched on the idea that by placing hot components near the surface of the case, we make it easier for the individual components to transfer thermal energy to the surroundings. Valve has gone one step ahead and used plastic shrouds and cowlings to direct the airflow for more optimal cooling.

CPU cooling shroud, upper left corner
CPU cooling shroud, upper left corner

In the usual shroud-less scenario, once cool air is blown over the heatsink and has absorbed thermal energy from it, it does not exit the case immediately. CPU coolers with a top-down airflow system blow the warm air in all directions; some of it escapes out of the case through the vents, the rest of it recirculates in the case until it finally escapes from one vent or another.

Top-down airflow system. Cool air (blue arrows) is pulled in from the top, warm air is exhausted in all directions from the bottom.
Top-down airflow system. Cool air (blue arrows) is pulled in from the top, warm air is exhausted in all directions from the bottom.

Needless to say, this is inefficient and can be improved on. But airflow management and thermal dissipation has always been a tricky problem, and what seems like straightforward solutions can sometimes give counter-intuitive results. In any case, let’s get back to what Valve is doing with those shrouds.

CPU cooling shroud, side view [MaximumPC]
CPU cooling shroud, side view [MaximumPC]

Here’s another view of the CPU shroud. There is a circular cutout to direct cool air from the top through the heatsink. The shroud prevents cool air above from mixing with the warm air below, and forces the warm air to escape the case through the only available opening: the vents in the top cover (not shown here; refer to second image in this post).

Laptop heatsink fan
Laptop heatsink fan

This, by the way, is exactly what laptop heatsink fans do: Pull in air from one opening, usually facing a vent on the bottom1, and blow it out through another opening, usually on the side of the case. For the Macbook Pros and Airs (the newer models anyway), the exhaust vent is along the screen hinge.

Mac Mini CPU cooler [iFixit]
Mac Mini CPU cooler [iFixit]

Other small-form-factor systems often use such shrouded coolers as well. The Mac Mini’s cooler pulls in air from the bottom (the side with the edge-vented metal plate), and blows it out through a narrow vent on the back.

Intel NUC cooler [Legit Reviews]
Intel NUC cooler [Legit Reviews]

Intel’s NUC system uses a shrouded cooler as well, pulling in air through a bottom vent and blowing it out through a grill-covered slot at the back.

If this is such a good way of doing things, why don’t we see it done anywhere else? Unfortunately, while some aspects of PC components are standardised, other aspects are not: the position of the CPU socket on ATX, micro-ATX, and ITX motherboards is not actually specified! By necessity it tends to be located in a particular region, but without knowing exactly where it is, or what kind of cooler the PC maker/DIY enthusiast is using, it is hard to mould a one-size-fits-all shroud.

However, once you know what parts you are going to use, it is possible to use shrouds and ducts for more effective airflow. And so we tend to see them used in mass-assembled systems. The Dell 660s that was mentioned in Part 1 uses a duct (similar to a shroud, but more tube-/funnel-like, and simpler). So do other custom-designed, mass-assembled systems, such as the Mac Pro, and most other prebuilt desktops.

Dell Inspiron 660s – CPU fan ducting
Dell Inspiron 660s – CPU fan ducting

Let us leave this topic for now, and revisit it again in later posts.

Further improvements #

If there’s one thing I still don’t like in ITX builds, it’s cabling. Even if it’s done neatly and well, it still feels like so much unnecessary wiring! There are ways to get round this, which I’ll hopefully cover in Part 6 or later.

Summary #

With the Steam Machine beta kit, Valve shows us one way of doing a high-end ITX gaming build right—with minimal wastage of space, and exploiting PC allometry so as to do away with case fans.

In the next part, Part 6, let’s really get to shrinking the desktop further, and see what we can do if we are willing to go without a separate graphics card.

On to Thresholds in computing: Part 6 – How much power does a desktop need?

See also

Thresholds in computing: Part 4 – Death of the desktop


  1. This is why one is usually discouraged from placing laptops on carpeted surfaces, or otherwise blocking the intake/exhaust vents.