| To say that there was an elevated level of excitement throughout the past year about the AMD Phenom is an understatement. Users all over the world scrabbled for information on what was to be AMD's latest and greatest foray into the processor world. Unfortunately the reality did not quite live up to the hype.
AMD was expecting to launch the initial Phenoms at a maximum clockspeed of 3 GHz. AMD had done a lot of internal changes to the base design to hopefully get the product to where it needed to go. Each core was internally optimized to increase both IPC and overall clockspeed on AMD's 65 nm SOI process. AMD also has been working diligently to improve the quality of their 65 nm process so it could hopefully handle this large and complex quad core part.
Unfortunately for AMD, things didn't work out as planned. The design does not seem to give enough leeway to advance clock speeds to a high level consistently, plus we have the very popular TLB errata that has branded the Phenom as a "sorta broken part". Until recently, it seems as though AMD has had major issues getting its 65 nm process up to speed. Only now are we starting to see 65 nm X2 parts that consistently can make it to 3 GHz and above at default voltage.
All is not lost at AMD though. The errata really only rears its head in very particular circumstances, though primarily in virtualization applications. Average users such as office productivity folks, gamers, and photo and video editing makers will likely never run into any issues derived from this erratum. The company is still producing rev. B2 parts successfully, and has been able to get quite a few of them to market. The Phenom 9500 and 9600 are priced at $199 and $239 respectively. These are the most inexpensive quad cores on the market so far. AMD has recently introduced the new Black Edition of the Phenom 9600. This fully unlocked part promises good performance at its designated clockspeed, but AMD is hoping that enthusiasts will enjoy the freedom to easily overclock these chips and buy them by the truckload.
Today I am going to attempt to overclock not only the BBE 9600, but also the Phenom 9900 (2.6 GHz) engineering sample that AMD was kind enough to send out to me.
Phenom Overclocking Basics
When the original Athlon 64 was released, there was a lot of confusion about how best to overclock this particular processor. Many people were not aware of how sensitive the initial chipsets were to setting higher HyperTransport speeds, or how memory scaled with increases or decreases in the core processor speed. Eventually people figured out that turning down the HyperTransport divisor, as well as decreasing the memory speed allowed the Athlon 64 to stretch its legs.
We are now hitting that same area with the new Phenom. People were expecting to hit high HyperTransport speeds with the release of the new HT 3.0 specification, and the availability of highly overclockabled (and cheap) DDR-2 memory would make overclocking the Phenom a breeze. This was unfortunately not true. Most Phenom processors and motherboards are crapping out when HT speeds reach around 212 MHz, with the most aggressive overclocks by professionals hitting 220 MHz. This is a far cry from the 330 MHz+ overclocks that the older Athlon X2s are able to hit (and higher when using these HT 2.0 parts with the new 790FX chipset).
Right now the best possible way to easily overclock a Phenom is to get an unlocked multiplier edition, and that means paying for the Black Phenom 9600. Luckily for users, the price of the BBE is the same as the standard Phenom 9600. The two differences between the products are that the retail product has a fan and heatsink and is multiplier locked (obviously). So if an enthusiast wants to see how far his chip will go, then the BBE will be a must.
The 2.2 GHz and 2.3 GHz Phenom parts are both listed as 95 watt units. The upcoming 2.4 GHz part is listed at 125 watts. This is a pretty hefty jump for 100 MHz, but from what I am seeing from my little perch... it is likely correct. These chips get toasty fast once they get past 2.3 GHz.
Phenom 9900 Engineering sample on left, 9600 Black Edition on right
When AMD was designing the Phenom, they chose to implement multiple clock domains, so some of the parts internally run faster or slower than others. There is a bit of confusion about how AMD was to implement this, as there were expectations that the "northbridge" functions (in this case the memory controller and L3 cache) would be able to run faster than the CPU cores, and they had their own separate power plane to draw from. Things did not work out in this situation. The northbridge part of the chip is actually running significantly slower than the CPU cores, and this is having a small effect on performance. The 2.2 GHz and 2.3 GHz parts have the northbridge running at 1.8 GHz, while the engineering sample 2.6 GHz part has the northbridge running at 2.0 GHz. This is not necessarily surprising since the memory controller was one of the bigger power hogs in the older Athlon 64 derivatives.
The split power plane is a good idea though, and it is better able to meet the growing power needs of these complex CPUs. It also allows a lot more granularity in controlling power consumption where power is the primary concern. Every AM2+ board out there now features a full 4 phase power delivery system, which should help smooth out any power ripples to these new processors. Theoretically this split plane design should help out overclocking as well.
For this little quick and nasty overclocking article I am using both the new Black Edition Phenom 9600 as well as the unreleased Phenom 9900 engineering sample. The motherboard is the Asus M3A32-Deluxe which is based on the AMD 790FX chipset with the 0603 BIOS. Here is the full list of components:
- Phenom 9600 and 9900
- Asus M3A32-Deluxe
- Corsair DDR-2 1066 @ 5:5:5:15 timings
- XFX 8800 GTX XXX Edition
- Seagate 7200.10 320 GB Hard Drive
- Lite-On DVD-R/RW
- Thermaltake Pure Power 600 Watt Power Supply
- Windows Vista 64 Ultimate
- AMD OverDrive 2.0.13 beta
The Grim Reality
If a user is expecting to get to 3 GHz with their Phenom easily, then they will be sorely disappointed. At this time I only had the use of the very good, but very stock cooler that AMD provided with this setup. Higher end coolers and water cooling equipment will produce better results than what I can show here, but even then getting to the higher speeds will be challenging.
I was only able to achieve a stable overclock to 2.8 GHz with the provided tools. With more aggressive cooling as well as pushing the voltage up higher than I was comfortable with, then 2.9 GHz and 3.0 GHz would be possible. Note that with the current BIOS and AMD OverDrive, there is no way to adjust the northbridge portion's multiplier. During all of this testing the NB ran at 2.0 GHz. So let's see how this processor scales with raising the clockspeed. At 2.8 GHz with 1.4v the chip quickly went above 60C with the cooling fan going as fast as it could.
Performance actually scales pretty nicely with the clock speed increases, but we have to wonder how much better it would have been if the NB portion was able to be clocked higher than 2 GHz. If I was willing to do a bit of hex editing on the motherboard BIOS, then I would have the ability to increase that multiplier. However, myself and the vast majority of users are not exactly comfortable messing around with the BIOS at such a low level and potentially bricking their motherboard.
We see a lot of strange results here. We get some increases in main memory bandwidth, but they are really variable. Only when looking at the cache performance do we see increases due to the L2 caches being clocked higher.
The Phenom 9600 runs at a core 2.3 GHz with the NB running at 1.8 GHz. As such we should expect scaling to be a little bit poorer, and overall memory performance down from the 9900. When I clocked this part to 2.5 GHz with 1.35v it also quickly exceeded 60C with the fan going full speed on the heatsink.
2.6 GHz was unattainable with the current equipment I have. If I had been willing to push voltage higher, it would likely have hit 2.6, but cooling becomes a big factor here. I was not fond of the idea of pushing the core above 70C, so I stopped at 2.5 GHz. I would guess with water cooling or peltier cooling that 2.7 would have been achievable, but 2.8 GHz is far from a guarantee.
I was curious as well to see how performance scaled with the NB running at a lower speed than in the 9900 sample.
We see something quite interesting here. If we scale these results for the 9600 to 2.6 GHz, it ends up being slower than the Phenom 9900 at a stock 2.6 GHz. For example the ALU performance of the 9600 @ 2.6 would be around 35,000 while the 9900 gets around 35,500 MIPS. This is not a huge difference, but we do see the effects of running the NB portion at a lower speed. In memory and cache performance, the difference is far larger.
The memory bandwidth for the Phenom 9600 is cut down by about 800 MB/sec from the 9900. The extra 200 MHz the NB on the 9900 has over the 9600 does have a fair sized effect on memory performance. Cache performance... not so much. It scales about how it should. Then again, all the L2 caches are run at full core speed.
Update from Ryan (12/26/07)
Josh wasn't the only one spending his holiday break with some AMD Phenom processors -- I spent a few days trying to overclock my new Phenom 9600 Black Edition processor as well. I saw "trying" because that's what it did to my patience...
Let me start by pointing you to Kyle's quick overclocking write up at HardOCP -- he was able to reach 3.0 GHz with his 9600 BE by pushing the CPU voltage up to 1.50v and running it on some pretty basic Koolance water cooling.
I then read the report that Josh submitted to me, that you read on the previous pages, and saw his identical processor refuse to overclock higher than 2.5 GHz. A 500 MHz different, 25% of the processors speed, is a pretty big gap so I set out to see if my Koolance water cooling setup would provide me with enough cooling to get something closer to what Kyle saw in his results.
It was not to be. If anything, my overclocking results are WORSE than what Josh described.
For my test bed I am using the MSI K9A2 Platinum motherboard with the latest BIOS provided by AMD and the Overdrive Utility version 2.0.12 as provided by AMD for use in Vista x64. When running at the stock clock speeds of 2.3 GHz, the Phenom 9600 was completely stable and seemed to be relatively cool under the collar.
At only 39C or so when under a full load for an hour, the Agena core is running without a drastic heat issue and that would lend itself well to good overclocking potential. Well, since others were able to hit 2.9 GHz and 3.0 GHz, let's just jump up to 2.6 GHz to get started...
Blue screen. Reboot. Hmm, guess we needed to up the voltage. Set to 13x multiplier for 2.6 GHz and this time set the voltage to 1.35v.
Blue screen. Reboot. Crap.
1.35v with a 12.5x multiplier for a 2.5 GHz clock rate. Lock. Reboot.
1.35v with a 12.0x multiplier for a 2.4 GHz clock rate. Success!!
I had this set to 1.45v attempting to go over 2.4 GHz...
But 100 MHz overclock isn't all that impressive, so after several more hours of the above scenario, I decided to switch motherboards. AMD recommended the new Gigabyte MA790FX-DS5 to me so I used that and the latest F3B BIOS to try overclocking this Phenom 9600 Black Edition again.
1.35v with a 12.5x multiplier for 2.5 GHz clock rate. Blue screen. Reboot.
My next several hours seemed like a rerun of a bad TV sitcom with my fiance wandering in trying to figure out why I was cursing at the Lord the day before his birthday.
I don't want anyone to think that I simply tried using the AOD utility a couple times and gave up either: I tried upping the voltages higher, upping the HTT voltages and DIMM voltages, I tried pushing the HTT up but couldn't get it to boot past 210 MHz, I tried applying both voltage changes and frequency changes at the same time and at different times, I even tried setting all these options in the BIOS directly rather than in the AOD software and instead of blue screens I got black screens as the OS refused to load.
I really, really, really wanted to get this CPU clocked higher, but simply couldn't.
Now look, I've never claimed to be an overclocking genius, and you won't see me on stage with Intel's CEO showing off my OC results ever, but I'm no n00b here. I've been overclocking for 8+ years and know a thing or two about and I would fully expect to be able to push my hardware to its limits.
After going through two motherboards and three BIOS revisions, I am pretty sure the I found the upper peaks to this particular Phenom.
My Phenom 9600 Black Edition limit: 2.5 GHz with a 1.35v Vcore that was stable ALMOST 100%.
Other Oddities
There are some other questions we have for AMD and the performance of their Phenom parts that will be addressed in the near future such as: what is ganged versus unganged memory and what are the advantages of each? Why is the TLB fix in the AOD software a friggin' button that isn't labeled?? Why is the HyperTransport 3.0 bus so limited in its scaling?
My Final Thoughts
Josh's conclusion sums things up pretty well but I will add that there is apparently a large swing in terms of overclockable parts out there. As I already told you, HardOCP was able to get 3.0 GHz out of their 9600 Black Edition, but most of the other overclocking results I have seen are on engineering sample CPUs. I think it will be quite some time before we can fully grasp how well these unlocked processors are going to fare in enthusiast's hands.
(We now return to the previous author...) Conclusion
There is a reason why AMD was unable to release a Phenom above 2.3
GHz at this launch, and it simply is because they do not appear to be
getting the speed bins in the power envelopes they were hoping for.
2.3 GHz is the highest speed Phenom that will be available for some
time yet, and the average overclock of one of these processors will
likely mimic my findings. 2.5 GHz is about the best that can be
expected with standard type cooling.
It is very nice that AMD is giving enthusiasts the ability to clock
up these processors with the unlocked multipliers. Especially
considering that HyperTransport overclocking on the Phenom is
essentially a bust at this time. If a user is hoping to overclock,
then getting a BBE 9600 is really the only option.
Phenom 9600 Black Edition
Performance at 2.8 GHz with my engineering sample is very good and
is faster than the Q6600 from Intel. In single and double threaded
performance it is probably a little faster than the older X2 6000+, but
when more than two threads are used then the Phenom really excels. The
9600 at 2.5 GHz is also quite competitive with the Q6600. Considering
that the 9600 in both flavors is now cheaper than the Q6600, it does
make it a viable option for those interested in the price/performance
bottom line.
Overclocking for the Phenom is still in its infancy, but AMD has
helped us out by offering this unlocked processor, as well as a very
solid overclocking utility with OverDrive. Most of the major
motherboard manufacturers have released BIOSes for their boards that
include the TLB fix. The latest version of AMD OverDrive does allow
the user to disable the fix for greater performance.
Getting an extra 200 MHz out of the BBE Phenom 9600 is not a
tremendous feat, but it does offer the user extra performance for very
little extra work. Things will get better as AMD sorts out their 65 nm
process and the upcoming revision B3 of the Phenom. Until then, the
Phenom 9600 is an interesting and well performing part for its price.
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AMD Phenom 9600 Black Edition Review and Overclocking Test
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