Low-Power Phenom IIs: Making HTPC Magic

In addition to the two dual-core processors being launched today, AMD is also unveiling a pair of low-power Phenom IIs: the X3 705e and X4 905e. Both chips run at 2.5 GHz, feature 2 GHz northbridges, and ship in Socket AM3 trim.

Of course, this means they have DDR2 (up to 1,066 MT/s) and DDR3 (up to 1,333 MT/s) memory support, depending on the platform in which you drop them. HTPCs based on the older 780G chipset (like the Maui platform below) will need a BIOS update to support these new processors.

Identical to the existing X3 and X4 processor lines in every way except power consumption, the two low-power models sport 64 KB of L1 data/instruction cache per core, 512 KB of L2 per core, and the same 6 MB shared L3 cache.

Nominal voltage is between .825 V and 1.25 V (for comparison, a Phenom II X4 940 BE runs between .875 V and 1.5 V). In essence, these are simply Phenom IIs that are able to run at 2.5 GHz “undervolted,” and hence push power consumption down to 65 W TDP levels.  

There is a price premium tied to the lower-TDP parts. The X4 905e is set to cost $195, while the X3 705e will launch at $125. For the price of the 2.5 GHz X4 you could buy a 2.8 GHz X4 920 (a 125 W part, though it'd also require an AM2+ platform), and for the price of the 2.5 GHz X3 you could get a 2.6 GHz X3 710 (a 95 W part). Is it worthwhile to lose 300 MHz in exchange for a near-halving of power consumption? How about losing 100 MHz to drop from 95 W to 65? For the folks concerned with heat output, we have to suspect the frequency sacrifice will be more than welcome for cooler running. Making the same jump in Intel's lineup (from Q8400 to Q8400S) costs an extra $62, pushing you to $245.

Going, Going, Back, Back, To Maui, Maui

I still haven’t forgotten about Part 2 of the HTPC/Windows 7 story I started earlier this year. It’s a sizable project, though, which has involved replacing a TV, replacing a receiver, and testing tons of hardware/software recommended in the comments you left for that first part.

There is one update I can provide right from the outset, though. I started that project with a Phenom X4 9350e quad-core chip running at 2 GHz with a 1.8 GHz northbridge. It included 512 KB total L1 cache, 2 MB total L2 cache, and a 2 MB shared L3 cache.

AMD provided a new BIOS not yet available through MSI that updates the Maui platform to support the company’s new low-power Phenom II X3 705e and X4 905e processors, which sport the same 65 W TDP as the 9350e we were using before. Swapping in the X4 905e bumped the system up to 2.5 GHz with a 2 GHz northbridge, and a 6 MB shared L3 cache.

The difference in performance is actually quite significant—if you’re considering spending more money on a low-power CPU, it’s probably for an environment like this one. And given a choice between the older 2 GHz Phenom at 65 nm and the X4 905e at 45 nm, the newer chip gets the nod. With Cool’n’Quiet and C1E enabled, the X4 905e idled at about 32 degrees Celsius (800 MHz, .95 V) using the quiet SilentFlux Media cooler that AMD shipped with its Maui demo unit.