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High performance PC with non-synchronous RAM timings?

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October 4, 2006 1:13:40 PM

Why would the PC maker Alienware, who is known for building fast systems, sell their "Ultimate Gaming Machine" with non-synchronous FSB to RAM timings?

They are selling these systems with only the Core 2 Duo with 1066 FSB and DDR2 memory that is only 800 MHz. With the CPU 1066 FSB with would put it's base FSB at 266 and the 800 MHz memory with it's base of 200 MHz, that should be significantly slower than using 1066 MHz DDR2 or even 533 MHz DDR2 memory mainly becuase with the latter, you would get the synchronous timings. Am I not understanding something correctly? Unless the speed is greatly faster, wouldn't the synchronous timings be more important and be a faster machine?
October 4, 2006 1:53:05 PM

Quote:
Why would the PC maker Alienware, who is known for building fast systems, sell their "Ultimate Gaming Machine" with non-synchronous FSB to RAM timings?

They are selling these systems with only the Core 2 Duo with 1066 FSB and DDR2 memory that is only 800 MHz. With the CPU 1066 FSB with would put it's base FSB at 266 and the 800 MHz memory with it's base of 200 MHz, that should be significantly slower than using 1066 MHz DDR2 or even 533 MHz DDR2 memory mainly becuase with the latter, you would get the synchronous timings. Am I not understanding something correctly? Unless the speed is greatly faster, wouldn't the synchronous timings be more important and be a faster machine?
The FSB is 1066 Quad Pumped(266x4). The RAM only needs to run at 533(266x2) to run synchronously. So DDR2-800(400MHz x2) is running async. (3:2) or 50% faster than FSB. That's plenty fast. :) 
a b } Memory
October 4, 2006 2:01:18 PM

The Core 2 Duo can make good use of the higher frequency - lower latency memory to give better performace even during async operation.
DDR2 800 (400Mhz * 2 data blocks per cycle) would have 3/2 RAM/FSB ratio at stock 266Mhz FSB. With the FSB overclocked to 333Mhz you could use the 5/4 ratio for DDR2 832Mhz (a light overclock). And of course pushing the FSB to 400Mhz would enable the idea 1:1 ratio.

Check out this article for specific examples of how the sync/async vs higher frequency arguement works out: Choosing the Right Memory for Core 2 Duo Platform - Part 1

For practical purposes the higher frequency DDR2 advantage won't be noticeable when gaming at higher resolutions when the GPU starts being the systems performance bottleneck. But media editing and other CPU/RAM intensive applications should get a small boost in overall peformance.
Related resources
October 4, 2006 4:23:10 PM

Remember that we are all assuming the RAM is run in dual-channel mode, which doubles the throughput. Your point about DDR2-1066 would be right for single-channel mode.
October 4, 2006 8:41:46 PM

Here's more info on choosing ram.
Madshrimps article
AnandTech #1
AnandTech #2

This came from Mondoman in an earlier post. Read it.

Quote:
(Msg. 3) Posted: Thu Sep 14, 2006 2:30 pm
Post subject: Re: Memory Nooob, aarrggghh! Using CPU-Z to set timings !!! [in reply to: FishBoi]

--------------------------------------------------------------------------------

There are 4 classes of memory speed/timing specs that often get confused with each other. From slowest to fastest they are:

1) SPD settings. Each DIMM has a small EEPROM that the DIMM manufacturer programs with one or more sets of timing info. These "SPD" values are read by the motherboard BIOS on bootup and used for "auto" memory speed/timing setting. Each SPD set of values assumes standard memory voltage (1.8V for DDR2) and lists a memory bus speed (e.g. 333MHz for DDR2-667 speed) along with timings for that speed (e.g. 5.0,5,5,15).
The DIMM is guaranteed to work at these SPD settings, but they are usually chosen to be somewhat conservative, to minimize MB incompatibility problems. Different DIMM manufacturers seem to have slightly different policies on SPD settings. For example, Kingston is known for compatibility (perhaps at some cost in speed) while OCZ seems to emphasize performance (perhaps at some cost in compatibility).

*Important Note:* Any "SPD" settings shown by a software tool (like CPUZ) *have no relation to the actual current speed that your memory is running at* - they are just reading out the values programmed into the SPD EEPROM. You need to look at a different part of your software tool to find the actual memory speed and timings in current use (IIRC, the "Memory" tab for CPUZ or the "Chipset" detail for PC Wizard 2006).

Bottom line: SPD settings are just average or slow speed settings chosen for maximum compatibility with motherboards.

2) Premium-line DIMMs can often run at faster settings than those in their SPDs, even under standard voltage. However, you will need to enter the memory bus speed and timings by hand, using the BIOS, overriding the "auto" setting. Different motherboards have different procedures for this. One key point to remember is that any memory can be set to run on a slower memory bus or with slower timings (bigger latency values) without any problems -- it's running faster that may cause problems.
***Important Warning***: When running memory faster than the SPD settings, ALWAYS use a good memory testing program like memtest86+ and a CPU/memory stress tester like PRIME95 to verify that your system is operating without errors. Otherwise, small errors and corruptions may accumulate unnoticed and eventually ruin your data and/or require a complete reinstall of the OS and programs.

Bottom line: You should be able to run your DIMM at the advertised speed and timings w/o changing the voltage, *as long as the DIMM is rated at standard voltage (1.8V for DDR2),* but you may have to enter the speed and timing settings manually using the BIOS.

3) Manufacturer-sanctioned overclocking. DDR2 memory is currently at the "bleeding edge" of memory development. Although a number of (official and unofficial) standards have been worked out, production chips and DIMMs don't always meet those standards. That doesn't mean the chips or DIMMs are without value, especially given the shortage of higher-speed parts. For example, it's very difficult to find 1GB DIMMs that will run at DDR2-800 at the standard 1.8V. However, manufacturers can now produce plenty of DIMMs that will run at DDR2-800 at a slightly higher voltage, say 2.0V. (Remember, 6 months ago, it was hard to find DIMMs that would run at DDR2-800 under *any* voltage -- this is life on the bleeding edge.)
Thus, they may sell the DIMMs as "DDR2-800" memory, and note in a footnote, or on a spec sheet, that they are only guaranteed to run at DDR2-800 at 2.0V. However, since it may not run at DDR2-800 at 1.8V, they program a slower speed as the max speed in the SPD, so the system will at least boot successfully. This is a major reason why people note that their "DDR2-800" RAM is running at a slower speed on "auto" settings.
When shopping for RAM, for a given memory bus speed (DDR-x or DDR2-x), the closer the spec voltage to the standard voltage (1.8V for DDR2), the better quality the RAM.
*Important note:* In order to be able to run at the manufacturer's spec speed, you need to get ALL the speed specs, including the *DIMM voltage,* from the manufacturer's packaging, web site, or tech support. Then, in your motherboard BIOS, FIRST set the DIMM/memory voltage to the manufacturer's value. Second, set the memory bus speed. Finally, set the timing values.
***Important Warning***: Too high a voltage can permanently damage RAM. Such damage can be identified as overvoltage damage by the DIMM manufacturer. Different manufacturers have different voltage limits on their RAM guarantees, so BE VERY CAREFUL NOT TO EXCEED THE MAX VOLTAGE if the warranty is important to you. IIRC, Corsair's XMS2 max voltage is 2.1V. OCZ guarantees much of its high-end memory to 2.2V. YMMV.
In practice, what this means is that, for example, you shouldn't mix a Corsair module rated at 1.9V in the same system with a Ballistix module rated at 2.2V, as running at the Ballistix spec voltage of 2.2V will void your Corsair warranty.
Recently, Corsair and nVidia have introduced a standard for automatic manufacturer-sanctioned overclocking that they call "EPP". This standard uses additional info stored in previously-unused areas of the SPD memory to provide compatible motherboards with more detailed, higher-performance RAM OC profiles, including memory voltage increases.

Bottom line: Unless your RAM and MB both support EPP, you will have to enter memory voltage, speed, and timings manually in your BIOS to match "factory OC" specs of your module. As long as you do not exceed the factory-specified voltage, the manufacturer will support OCing a module under warranty. However, if you mix different modules in the same system, make sure the necessary voltage for one module does not exceed the limit (and thus void the warranty) for a different one.

4) "Real" overclocking. Finally, in secret workshops running outside any manufacturer limits, this is the real thing! Many DIMMs modules can actually run reliably at faster speeds and/or timings than in their spec. In general, the higher-end product lines are built using better DIMM PCBs and higher-spec RAM chips, and so have more OC potential. "Value" lines are not designed with OC in mind and typically have poor OC potential. However, for mature RAM technologies (like DDR now), sometimes ALL of the chips are high-spec, and thus even "value" DIMMs may be significantly OCable.
There are plenty of guides out there on how to OC, but there's one aspect people often forget: this techonology changes QUICKLY! Especially on the bleeding edge, just because a review OCed a DIMM by 50% doesn't mean you can do the same, even if you get the same part number. Manufacturers continuously make changes to the components, chips, and SPD programming that make up a DIMM, not to mention the chip-to-chip variations as fab conditions are tweaked, etc. RAM reviews even a few months old are best treated as historical documents, not as guides to today's buying decisions.
***Warning***: As pointed out in section (3) above, higher-than-standard memory voltages can and will damage the memory and/or shorten its life. Any OCing done by exceeding the manufacturer's limits on your DIMM will void its warranty, so be prepared to pay out of pocket for any failures caused by your OCing.
_________________
NI8-SLI/P4 805D @184 MHz FSB (3.68 GHz core)
2x 512MB Ballistix DDR2-800 (run @DDR2-600, 3-3-3-1T)
AC Freezer 7 Pro + ghetto fans 'n sinks for PWM
MSI 7600GS & UV bling!

Last edited by Mondoman on Fri Sep 15, 2006 12:00 am; edited 1 time in total
October 5, 2006 1:14:15 PM

Thanks for the link to the X-bit Labs article; it was very informative.

It seems like there is some performance gain from running a higher memory clock speed even when it is asynchronous, but it is not a significant performance gain.

The article did then comment that when the CPU clock core is OC'ed to 400 MHz while running DDR2 800 MHz, there is significant performance gain (which is expected), but very little performance gain with memory faster than 800 MHz.

Quote:
More interesting are the results of the overclocked platform. In this case, there is more sense in using fast memory and the optimal memory frequency divisor is 1:1 (FSB:D RAM) as has been shown in our tests. In other words, you can achieve maximum performance by using memory with lowest possible timings in synchronous mode. It means that if you overclock the FSB to 400MHz, DDR2-800 SDRAM with low timings is the optimal choice. If the FSB is overclocked more, DDR2-1000 or DDR2-1067 SDRAM is the best option. An additional argument in favor of using memory and the FSB in synchronous mode at overclocking is that the 1:1 divisor is the most stable one on a majority of mainboards.


It seems as though faster memory will always give performance gains, but asynchronous settings will only give marginally better performance and less stability. It seems as though synchronous settings are still kind of the sweet spot for stability and speed.
October 6, 2006 2:57:50 AM

Quote:
...
It seems as though faster memory will always give performance gains, but asynchronous settings will only give marginally better performance and <u>less stability</u>. It seems as though synchronous settings are still kind of the sweet spot for <u>stability</u> and speed.

Stability isn't affected by being synch or asynch.
October 6, 2006 3:05:17 AM

Actually, I didn't think it was either; I was more or less referring to the article and looking for confirmation from others on that.

Thanks
October 6, 2006 4:33:43 PM

At 266 FSB, DDR2-800 offers marginal performance gains over DDR2-533 because DDR2-533 has a clock speed of 266 MHz--the same as the FSB. Therefore, DDR2-800 would be bottlenecked by the 266 MHz FSB. The main reason that DDR2-800 is still a little faster than DDR2-533 at 266 FSB is that it has lower memory latency. So if the FSB is overclocked to 400 MHz, DDR2-800 would have the same bandwidth. Everything under DDR2-800 would bottleneck the FSB, but everything above DDR2-800 would be bottlenecked by the FSB. And again, everything above DDR2-800 would only have marginal performance gains because of this, just like everything over DDR2-533 would have marginal performance gains at 266 MHz FSB.
October 8, 2006 1:17:23 PM

An additional thought.

If one doesn't plan to O/C, then DDR2-667 RAM is the worst choice for a Core 2 Duo CPU due to the asynchronous timing - even DDR-533 is faster.

Fair observation?
October 8, 2006 1:27:36 PM

Quote:
An additional thought.

If one doesn't plan to O/C, then DDR2-667 RAM is the worst choice for a Core 2 Duo CPU due to the asynchronous timing - even DDR-533 is faster.

Fair observation?
Exactly. If it's cheap, it would be okay to buy it, and just run it at 533.
October 8, 2006 7:02:45 PM

No 667 would be faster than 533 because of the lower latency
October 8, 2006 7:21:30 PM

Fair observation Max789, but you need to be thinking of the future. Let's say a year from now you upgrade your cpu, chances are that cpu will have a 1333 FSB. Your ram at 533 is now behind the game unless you OC it. The 667 you can run it at 533 and be in sync and still be in sync when you get a new cpu.
BTW - when I bought my Patriot 667 ram 2 weeks ago it was cheaper than any comparable quality 533.
What I'm saying is don't automatically disregard 667.
October 8, 2006 8:59:25 PM

Can some1 confirm what I said about DDR2-667 being faster than DDR2-533 at 266 MHz FSB?
It seems like everyone believes that DDR2-533 is faster. Am I wrong?
October 8, 2006 9:19:08 PM

Just look at these results. Also look at these. Doesn't quite follow the same results as the first test. IMHO I don't think you'll notice the differnce in real world apps between 533 and 667. You'll probably have other components slowing down your system (ie, HDD/GPU) before the ram is your bottleneck as long as you have plenty (2GB or more) dual channel ram. I chose my 667 based on price and future upgradeablility. Again, this is just my opinion.
October 9, 2006 5:56:22 PM

667 CAS 3 would be great for when 1333fsb (333) becomes the norm. I purchased 800 CAS 4 to overclock my conroe... It can be downclocked to 667 CAS 3. 8) So im set
October 9, 2006 9:36:24 PM

Quote:
667 CAS 3 would be great for when 1333fsb (333) becomes the norm. I purchased 800 CAS 4 to overclock my conroe... It can be downclocked to 667 CAS 3.

That's what I'm talikng about. 533 is nice now but not much room for the future.

Peace Out!
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