[Discuss] mini-ITX boards for Haswell CPUs

[tmetro+blu at gmail.com (Tom Metro)]

Richard Pieri wrote:
> Tom Metro wrote:
>> My understanding is that Haswell uses yet another incompatible socket
>> format, so I don't think you can plug an "old i3" onto these boards.
> 
> That's intentional. Haswell's TDP is about half that of Ivy Bridge. If
> you were to wire a Haswell CPU to a Ivy Bridge socket you'd burn out the
> CPU.

It sounds like you're conflating power dissipation with exceeding a
device's voltage limits. There is often a correlation between voltage
and power consumption, due to practical constrains of voltage drop and
maximum current you can run though a particular size conductor.

But in the same way you can plug either a 100 W or a 40 W bulb into your
120 V outlet, you can plug a lower TDP CPU into a motherboard designed
for higher TDP parts. The CPU will only draw the power it needs. Just
look at the product family specs for Haswell or prior families and
you'll see Intel makes parts with a variety of TDPs even within the same
socket family.

(Going in the opposite direction - trying to draw more power than the
board was designed for - obviously would cause problems.)

You could make a case that Ivy Bridge socket might supply too high of a
voltage, but as it turns out Haswell CPUs have an integrated voltage
regulator:
http://www.eetimes.com/electronics-news/4415059/Intel-Haswell-packs-integrated-voltage-regulator

so in theory you could plug it into a mother board designed to supply
higher voltages and it would regulate down to the level the CPU requires.

But programmable regulators are commonplace on modern motherboards, so
that really isn't an enabling technology for making the Haswell
compatible with existing sockets. (The motivation for the on-die
regulator was to "lower the bill of materials and motherboard footprint"
and increase power efficiency.)

So I don't think it was power supply incompatibility that led to the
need for a new socket specification.


> If you were to wire a Sandy Bridge or Ivy Bridge CPU to a Haswell
> socket, it wouldn't have enough power to run.

Yes, that I buy.


> If you want specs, look at the CPU models, not the boards they go on.

They should still list the DAC specs, and even if they said "see CPU for
GPU specs" it would still make it clear that the board facilitated
onboard graphics.

 -Tom

-- 
Tom Metro
Venture Logic, Newton, MA, USA
"Enterprise solutions through open source."
Professional Profile: http://tmetro.venturelogic.com/