Intel marketing announces that it can attach smaller meaningless numbers to its hardware than before

Intel desperately wants to get its hardware into tablets.  The problem is that Ivy Bridge and Haswell put out far too much heat to be reasonable for a tablet, while Atom performance in Windows is just dismal.  The next generation Silvermont Atom may be a decent competitor for AMD's Temash, but it will have to be cheap, and Intel doesn't like cheap.

So what's Intel to do?  Why, make up meaningless numbers to throw out there, of course.  A year or so ago, Intel announced that Haswell would have a 10 W version.  When Haswell launched, Intel said, oh sorry, it's actually 11.5 W.  But our marketing department has made up a 6 W figure that doesn't actually mean anything, and 6 is actually even less than 10.  Today's announcement of a "4.5 W" Haswell part just means that Intel's marketing department figured out how to take an 11.5 W part and stick a 4.5 W number on it that still doesn't mean anything.

Now, in Intel's defense, chips usually use far less than their TDP.  So they invented a "Scenario Design Power" to say that under active use, the chip sometimes uses a lot less than its TDP.  So the 11.5 W chip with an SDP of 6 W might well only put out 6 W in typical active use.  So Intel wanted to emphasize the smaller numbers.  But you know what other chips typically use less than their TDP?  Basically all of them.

The meaning of TDP is that it's the manufacturer's promise that if your system can handle this much power delivery and this much heat output, it will be safe.  That's why TDP stands for Thermal Design Power:  this is the number you need to design around for thermal purposes.

If you design around the SDP, you probably end up with overheating problems sooner rather than later, and quite possibly dead hardware.  Sometimes the chip won't use more than 6 W.  So if your tablet can handle 6 W of heat output and no more, sometimes it will be safe.  But only sometimes.  Sometimes it will fry.  And that's bad, which is why the Sometimes Design Power doesn't mean anything.

That's why, if you're going to build a tablet around a Haswell chip, you have to design it to be able to handle 11.5 W.  The weight and thickness will be dictated by the 11.5 W part inside.  It doesn't matter if it has an SDP of 6 W or 4.5 W or 2 W or any other number that Intel marketing can invent.  You have to be able to handle 11.5 W or you risk overheating.

Want a smaller, thinner tablet than you can build around an 11.5 W part?  AMD offers an 8 W version of Temash.  And also a 3.9 W version.  Those are real TDPs, not some meaningless marketing number like Intel's SDP.  The upcoming Silvermont Atom will have TDPs in that ballpark, too.

And really, 11.5 W is an awful lot for a tablet.  Which is why you don't want a Haswell tablet.  Today, if you want a Windows tablet, you want AMD Temash--and for someone to actually release such a tablet, which oddly hasn't happened yet as far as I can tell.  Eventually you may want Intel Silvermont Atom.  Or you may still want AMD Temash even after Silvermont Atom launches.

Or, of course, you could get an Android or iOS tablet running an ARM chip on however little power you desire.  Or decide that you don't want a tablet at all.  But regardless, you don't want a Haswell tablet.