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AMD Phenom-II X4-840 CPU HDX840WFGMBOX E-mail
Reviews - Featured Reviews: Processors
Tuesday, 04 January 2011
Table of Contents: Page Index
Features and Specifications
Closer Look: Phenom-II X4-840
Testing and Results
AIDA64 Extreme Edition v1.1 Benchmark Tests
Passmark PerformanceTest
PCMark Vantage Benchmark Tests
SiSoftware Sandra
Cinebench R11.5 Benchmarks
Street Fighter IV Benchmark
Video Transcoding Tests
AMD Phenom-II X4-840 Final Thoughts
AMD Phenom-II X4-840 Conclusion

Closer Look: Phenom-II X4-840

The Phenom-II X4-840 is really an interesting processor and it deserves a closer look. The first word I got about the Phenom-II X4-840 was that AMD was bringing back the "800-series moniker" with a budget priced quad-core Phenom-II without the L3 cache. What that sounded like to me was a Deneb based CPU that didn't quite meet production standards on the L3 cache, so it was disabled. I was looking forward to getting my hands on one of these chips, especially to see if I could unlock the L3 cache and make it a full-fledged Phenom-II, cache and all.


As I started getting more information on the Phenom-II X4-840, I realized it wasn't quite what I had expected. Even with the Athlon-II X4 series, you will occasionally come across a chip that was made on a Deneb die with a failed L3 cache, but they are generally built on the Propus die. Well, come to find out, the Phenom-II X4-840 is also built on the Propus die, although I am sure that some X4-840s will be shipped from failed Deneb dies.

With all that in mind, lets a take a look at the technical specifications of the Phenom-II X4-840 and see how they match up to other Phenom-II CPUs.

Propus Die - Athlon-II X4 Processors

Again, the Phenom-II X4-840 is built on the Propus die according to the specs released by AMD, but the Deneb die based on CPUZ. The Propus die is 169mm2 and is built on the now common 45nm process with the Athlon-II X4 average of around 300 million transistors. That's a far cry from the Phenom-II X4 series' 758 million transistors and 258mm2 die size. The max TDP of the Phenom-II X4-840 also matches the Athlon-II X4 series at 95W rather than the 125W of the Phenom-II X4 series. The rest of the specifications match both the Athlon-II X4 and Phenom-II X4 series. Processor bandwidth is up to 37.3GB/s with DDR3 memory, supported memory is at 1066MHz for DDR2 and 1333MHz for DDR3, the memory controller doesn't change, nor does the HT link at 4.0GHz full duplex. Really, the only other difference is the lack of the L3 cache, which is present for all other Phenom-II X4 processors.

Deneb Die - Phenom-II X4 Processors

To be clear, the Phenom-II X4-800 series isn't a new thing. Back in early 2009, AMD was releasing Phenom-II X4-800 series processors in their complete line-up of CPUs. Back then, the Phenom-II X4-800 series was built on a Deneb die (like all other Phenom-II X4 processors) and had 4MB of L3 cache, compared to the 6MB of L3 cache on the 900 series. Around the end of the summer of 2009, AMD stopped releasing the Phenom-II X4-800 series.

Fast forward to January 2011 and we see the first Phenom-II X4-800 series processor released in over a year, but with significant changes. The 800 series now looks like a Athlon-II X4-600 series with a different name. In fact, if you go by the numbers, the Phenom-II X4-840 should be named the Athlon-II X4-650. The only difference between the X4-840 and the X4-645 is the standard 100MHz clock speed bump.

Call it whatever they want, if the Phenom-II X4-840 releases at $102 as has been announced, it now becomes faster than the highest speed Athlon-II X4 processor and will sell for about $17 less (as of December 28, 2010, the Athlon-II X4-645 was selling on for $119). Let's see what the tests say about the Athlon-II X4-650. Whoops, I meant Phenom-II X4-840.

The most recent Athlon-II and Phenom-II processors have been great overclockers. There is a lot of headroom and it isn't uncommon to see a 20% increase in clock speed for a stable overclock. Though I'm still not really sure what to call the Phenom-II X4-840, I'm going to treat it like an Athlon-II X4 CPU. The Athlon-II X4-645 went from 3.1GHz to 3.8GHz overclocked, and I expected similar results from the Phenom-II X4-840. Since the X4-840 isn't a Black Edition processor, the multiplier is locked out at x16. This doesn't stop us from overclocking, we just have to work around the multiplier by increasing the CPU/HT reference clock speed.

Many of our readers have recently asked me about undervolting a CPU in order to make it as utility friendly as possible. Not much is getting cheaper these days, and the price of electricity is on the list of utilities that continue to increase in price and make our lives that much more stressful. When a CPU can run at stock speeds but on less voltage than it is set for, you will see a decrease in the amount of energy the processor uses. With the Phenom-II X4-840 processor, I was able to set the voltage to 1.2v, down from a normal 1.4v, and run it stably at the stock speed of 3.2GHz.


After playing with the bus speed since the Phenom-II X4-840 isn't a black edition processor, I was able to achieve a stable overclock of 3.9GHz. To do this I increased the bus speed to 245MHz. I was able to go quite a bit higher than this and still boot into Windows, but the X4-840 didn't remain stable under stress testing at anything higher than 3.9GHz. I also needed to increase the CPU voltage to 1.6v in order to attain this overclock.



# You tell it like it isBernardP 2011-01-04 06:09
Congrats for telling it like it is. I have read another review that glosses over the renaming trickery.

However... the Phenom II 840 is not "a wolf in sheep's clothing", as you say, but more of a sheep in wolf's clothing :-)

It should be called a Athlon II 650, without a doubt. This renaming brings shame to AMD.

No doubt we will see the likes of HP and Acer peddling this Phalse Phenom to the gullible masses.
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# Marketing at it's finestComputer Ed 2011-01-04 07:52
That in the end was the reason for it. My sources at AMD hinted that the name change was asked for by the partners. However as I understand it the 800 series will be the replacement as it where for the Athlon II line.

On a different note I am curious how many people complained when the the i5 was moved from the quad core as it originally released to a dual? Did anyone cry foul then?
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# I agreeHank 2011-01-04 12:10
I mentioned in my review of the i5-2500K that I was glad for the newer transparency with the Sandy Bridge CPUs where all i5 chips are quad-core with no hyperthreading. It's disappointing that they don't have hyperthreading, but at least we know what to expect when buying an i5 this time.
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# What about the "real" Phenom II?Olle P 2011-01-14 06:37
I think the most intriguing result of this test is how little extra performance is gained by adding 6MB L3 cache and hiking up the clock speed from 3.2 to 3.6 GHz (the specs of the 975).

The difference in actual results is mostly way below the 12.5% expected by the clock speed alone.

Seems like the only reason for spending the extra money on a "real" Phenom II X4 is to get a Black Edition with better overclocking.
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# replyNormal 2011-01-20 14:17
@Olle P

Do not forget the L3 cache is suited for memory intensive tasking.
So just a clockspeed application a faster Athlon will beat a lower clocked Phenom,but whenever memory (Cache) comes in play a slower Phenom will beat an even higher clocked Athlon handsdown.
That's why in certain games the smaller P2X2 560 will beat the Athlon 2X4 645 .
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# MrDavid Richmond 2011-05-20 10:24
I built a new pc around a 840 cpu.I was going to use a i3 clarkdale originally but when I went to buy the supplyer only had the new sandybridge as I was on a tight budget I took the amd route instead.A great choice fsst at most tasks and cheap.
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