I have been looking in vain for review of this CPU, all the attention is focused on the unlock-ability of the second core.

But I'm more interested in the power efficiency of the CPU !

any one?

You can not have a very good efficiency if one core is locked even if you do not use the second core it will still take some current.
More core better efficiency if the same technology was used to produce the CPU an if the application you use can take advantage of multi thread.
Efficiency is complicated to define if your computer spends 99% at idle then an efficient CPU will have very low idle power consumption. And the rest of the system is maybe even more important (Motherboard, HDD, and power supply).
But I will be also interested in the power consumption of this CPU.

It's pretty efficient but it's still the same as a celeron. I'd stay away from it.

I have a Sempron 140 on a Gigabyte MA785GM-US2H motherboard running Windows 7 32 bit with 1 gig of RAM. It's slightly undervolted.

There's a little utility called EasySaver that comes with the board and displays the CPU power. Whenever I've looked at it, it read from just below 13 watts to no more than 17, and that included either DVD playing or Netflix streaming (don't remember which).

I'll leave it to others to decide whether that gives any indication of what the efficiency might be.

Does anyone know how the Sempron 140 compares to the LE series such as the Sempron LE-1250 or Athlon LE-1640 in terms of power consumption?

I have a Sempron 140 and experimented with underclocking and core unlocking.
At stock settings, unlocking the second core (which was prime stable) resulted in an additional 13/20 watts (idle/load) AC input power (80+ rated supply). While I agree that the under-load per-instruction energy is lowered by unlocking the core (or just buying the Athlon II x2), I strongly believe that the idle savings for normal (non SETI/folding/etc) machines means that there would still be net power savings in single core mode. Then again, with the 405E etc becoming available, a 45W x3 may change things a bit. Where is my 25W single core? :)

My Sempron 140 runs a single core at -.3V (1.05V) stable at stock clocking. I currently run it at 1.05V core and 0.975V (-.15V?). I use Cool'N'Quiet under Ubuntu 9.10 to scale from 800MHz to 2.0GHz. With a DVD burner, active PCI wireless connection, 1x2GB DDR2 800 RAM, ASUS M4A785-M motherboard, and a 8GB flash drive (boot device):
41W idle
46W mprime burn-in
Not sure where all those idle watts are going, but I've determined (through removing components) that about 32W is going to the mobo/processor... I'm not sure if a 785G is power hungry in general, or if the ASUS board wastes power. I would have expected this to be closer to the 760G <30W idle setups people have been raving about. Oh well :)

The CPU temperature hits a max of 28C with the stock HSF running @ 1700RPM, which is much quieter than my supposedly (read: not at all) 19dB 120x25mm case fan. I had to take the sticker off the stock fan because it was off-center and causing vibrations. Otherwise the stock HSF is pretty great at low speeds.

To the OP:
It depends what you are doing. If you need multipurpose processing for data, you probably want to look at the 400E / 405E 45W Athlon II X3 which are appearing now (January 2010). If you are just playing videos, you might consider hardware decoding of whatever you want to watch through either a nicer chipset or discrete graphics. But then, these may waste some watts... And if all you are doing is NAS, you probably won't saturate any processor, so think more about idle power + setup costs (and ECC + whatever other features you need).

Forgot to respond to this..

The Sempron 140 is a Regor Athlon II X2 with one core locked. It has been a pleasure to work with, and for light gaming, internet browsing, and basic HTPC use it has been a dream.

I don't know what the modern incarnations of the Celeron line are like, but I am heavily biased against those of the late 90s, and, based on your comment, you don't seem to think very highly of them. Calling Sargas (Sempron 140) "the same as a celeron" is weird (is a Athlon II the same thing as Core 2?), inaccurate, and understates the functionality of the chip!

Guess you never had your hands on Celeron E3300 they overclock like mad,run quiet and cool,power effcient. There not i7 but not everyone wants power sucking 125 watt CPU. I just a bought Sempron 140 resently for basic use and for $34 single core chip it's pretty decent.

n-n-n-necro post
Still love my sempron 140.

And I agree, modern celerons are not the hideous sluggards of yester-year.

I know but I couldn't let the budget CPU bashing go on E3300,Sempron 140 are great CPUs for $34,$49 CAD. E3300 is nothing but C2D E5200 Wolfdale with half the cache and is nice for us broke guys.

Celerons shouldn't be bashed just for the name Celeron. There are good ones, old and new. E3300 of today and I'm sure some still remember the legendary Celeron 300A.

As if celeron equals suckage. Id much rather have a modern celeron than that old sempron based on 2009 technology.

I have an unlocked Sempron 140 in this mainboard which in turn is sitting in this box with 8GB of Mushkin DDR3-1333, a WD 1TB green drive, an OCZ 60GB Vertex 2, and an X-fi ExtremeMusic under the hood.

According to my trusty Kill-o-watt that entire system draws about 89-92W just sitting there doing nothing. With the second core locked, it idles at... exactly the same wattage! I haven't tested load wattage.

To be honest, I was really hoping the sempron 140 would draw a LOT less juice than it does considering I have a Phenom II X4 840 (the "fake" PII with no L3 cache) based server box that's loaded down with a metric crap-ton of installed gear and hard drives and it idles at a mere 115W.

cortexodus -- The PSU in that Antec Fusion is years old, and its efficiency was not even 80% when new, so that's probably responsible for a lot of the high power demand. Also, is CnQ? I have a Phenom II 4-core 95W in a similarly minimalist PC that draws ~45W AC idle, but this is with a 500W 80+ Gold PSU, and CnQ enabled.

I guess I never thought about the age of the PSU, but you're right. I bought that Antec Veris unit back in... probably mid-2007? Anyway, yea CNQ is enabled and the core isn't overclocked or anything, just unlocked (reads as a Athlon X2 4400e). I have considered replacing the PSU in the past (although less as a consideration for age and more for a lack of wattage that would drive a nice video card) but the barrier to replacement has always been that it has some custom wiring bits comign out of the 24pin connector that deal with providing power to the case's front panel. I could probably mod a new PSU by yanking the necessary stuff off of the old one. Might not be a bad idea