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AMD Processors and Memory Divisor Question

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Last response: in CPUs
October 29, 2008 1:11:44 PM

I recall a while back; either a tom's article or a forum posting regarding particular processors that maximize memory performance by fully utilizing the fsb of the memory. At the time, I believe the 3800, 4600, 5400 and 6000 models were the most effecient because of the full use of the 800mhz fsb. Each of those processors for example are 400 mhz apart and at 2.0, 2.4 and 2.8ghz respectively. The 6000+ is no longer a candidate, as the core changed to 3.1ghz with the latest revision.

Could someone please clarify the reasoning behind this? I'm a bit rusty lately and have been unable to locate the article or forum posting which explained this in detail. I need this because I'm looking at upgrading my processor from an x2 3800+ (am2) and want the most bang for the buck. Thanks!

-- MaSoP

More about : amd processors memory divisor question

October 29, 2008 1:50:05 PM

It's rather quiet simple. The memory divider is half of the CPU multiplier, rounded up to the nearest whole number. So, the 6000+ is 3Ghz, the old one anyway. Well, all AMD cpu's have a FSB of 200Mhz. So, 3000Mhz/200Mhz = 15
and 15/2 = 7.5 (rounded up to the nearest whole number is 8)

The multiplier of the CPU is 15, so the memory divider is 8 (7.5 rounded up because the memory divisor has to be a whole number, aka an integer) Now, divide the speed of the processor, 3000Mhz, by the memory divider, 8. 3000Mhz/8 = 375Mhz. 375Mhz is the speed of your RAM, and since it's Dual Data Rate, multiply that by 2. 375Mhz * 2 = 750Mhz. Your RAM will run default at 750Mhz with the 3Ghz 6000+. But, you can simply up your FSB a tad to make it run at 800Mhz. A FSB of 214 would run your RAM at 401Mhz. Changing your multiplier will also change your results.

For the 5400+ (2.8Ghz):

2800Mhz/200 = 14
14/2 = 7 (no need to round up, already an integer)
2800Mhz/7 = 400Mhz
400Mhz * 2 = 800Mhz RAM by default, but you can always OC! Wooo!

lol, I hope that helps
October 29, 2008 2:20:18 PM

arson94 said:
It's rather quiet simple. The memory divider is half of the CPU multiplier, rounded up to the nearest whole number. So, the 6000+ is 3Ghz, the old one anyway. Well, all AMD cpu's have a FSB of 200Mhz. So, 3000Mhz/200Mhz = 15
and 15/2 = 7.5 (rounded up to the nearest whole number is 8)

The multiplier of the CPU is 15, so the memory divider is 8 (7.5 rounded up because the memory divisor has to be a whole number, aka an integer) Now, divide the speed of the processor, 3000Mhz, by the memory divider, 8. 3000Mhz/8 = 375Mhz. 375Mhz is the speed of your RAM, and since it's Dual Data Rate, multiply that by 2. 375Mhz * 2 = 750Mhz. Your RAM will run default at 750Mhz with the 3Ghz 6000+. But, you can simply up your FSB a tad to make it run at 800Mhz. A FSB of 214 would run your RAM at 401Mhz. Changing your multiplier will also change your results.

For the 5400+ (2.8Ghz):

2800Mhz/200 = 14
14/2 = 7 (no need to round up, already an integer)
2800Mhz/7 = 400Mhz
400Mhz * 2 = 800Mhz RAM by default, but you can always OC! Wooo!

lol, I hope that helps


That is exactly what I was looking for.

So, my conclusion is now that for someone NOT overclocking like myself, the 5400+ is the most effective and best bang for the buck of the standard X2 models. However, for those who ARE overclocking, it shouldn't make much of a difference since they can make up for the difference by modifying their bios timings to increase the memory speed to 400 or right around 400? Thanks for the reply!

-- MaSoP
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a c 134 à CPUs
a b } Memory
October 29, 2008 2:35:37 PM

I believe this is the article you are looking for.

http://www.tomshardware.co.uk/amd-reinvents-itself-uk,r...

I'm not sure its as big a problem as some make it out to be. The difference in speeds between DDR2-756 and DDR2-800 can't be that much. Synthetic memory benchmarks will say its huge, but losses in actual programs will be small.
October 29, 2008 3:07:51 PM

Yea, the real world difference of 50Mhz in RAM speed won't be noticeable. Also, the new 6000+ that's 3.1 GHz is a different core than the 6000+ that's 3GHz. The 3GHz 6000+ is a Windsor core on 90nm technology. The new 6000+ at 3.1GHz is 65nm but I've never seen it's core specified, I don't know if it's Brisbane or what. However, the old 6000+ would probably perform better as it has 2x1MB cache compared to the new 6000+'s smaller 2x512KB cache. However, the new 6000+ @ 3100MHz, the RAM would run at 775MHz by default.
October 29, 2008 3:30:01 PM

If you're really looking for the best ram performance, your best bet is to pick up some ddr2-1000 or ddr2-1066 and run the HT at 4x250 instead of 5x200. It's very easy to take the 5400 processor from it's stock multiplier of 14x200 to 12x250 and run it at 3.0ghz. Most wouldn't even require any addition voltage or anything. Don't forget to drop the HT multiplier to 4x for most boards, though (although I've had my HT stable at 5x300).
a c 134 à CPUs
a b } Memory
October 29, 2008 6:00:44 PM

The problem is 50MHz difference in ram + 50% smaller L2 cache + increase in L2 cache latency = weaker chip. 100MHz extra on the chip speed isn't going to overcome all this. I'm not sure how much slower the new 6000+ is, but for memory intensive apps I wouldn't be surprised to see/hear as much as 10% slower. (most apps would be less.)
a c 217 à CPUs
a b } Memory
October 29, 2008 6:30:25 PM

masop said:
I recall a while back; either a tom's article or a forum posting regarding particular processors that maximize memory performance by fully utilizing the fsb of the memory. At the time, I believe the 3800, 4600, 5400 and 6000 models were the most effecient because of the full use of the 800mhz fsb. Each of those processors for example are 400 mhz apart and at 2.0, 2.4 and 2.8ghz respectively. The 6000+ is no longer a candidate, as the core changed to 3.1ghz with the latest revision.

Could someone please clarify the reasoning behind this? I'm a bit rusty lately and have been unable to locate the article or forum posting which explained this in detail. I need this because I'm looking at upgrading my processor from an x2 3800+ (am2) and want the most bang for the buck. Thanks!

-- MaSoP


AMD Athlon X2 4850e 2.5GHz 2 x 512KB L2 Cache Socket AM2 45W: $60
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
- drop the HT to x4 and bump the clock to 224MHz (= 2.8GHz and 800MHz ram)

or

AMD Athlon 64 X2 5600+ Brisbane 2.9GHz 2 x 512KB L2 Cache Socket AM2 65W: $80
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
- drop the HT to x4 and bump the clock to 221MHz (= 3.2GHz and 800MHz ram)


You could snag one of the X2 6000+ models and bump the clock for an overall speed of 3.2GHz to bring your RAMs up to spec. In some cases it does make a difference (the first thing that comes to mind is the game UT3 which in my testing got a nice little bump with an increase in ram speed)

Since you won't be OC'ing the X2 5400+ will work just 'dandy' - but if you do OC in the future you will have to drop the mem ratio 400-->333 (and at 3.2GHz your RAMs would then be 761MHz be cause of the '7' divisor).
October 29, 2008 6:52:36 PM

4745454b said:
The problem is 50MHz difference in ram + 50% smaller L2 cache + increase in L2 cache latency = weaker chip. 100MHz extra on the chip speed isn't going to overcome all this. I'm not sure how much slower the new 6000+ is, but for memory intensive apps I wouldn't be surprised to see/hear as much as 10% slower. (most apps would be less.)


So, which of the following is the best choice; all from NewEgg of course:

5400+ @ 2.8GHz (65 watts) $77 (free s/h @ NE)

5600+ @ 2.9GHz (65 watts) $80 ($14.90 s/h @ NE; inflated!)
5600+ @ 2.9GHz (65 watts) $83 (free s/h @ ZZF)

6000+ @ 3.1GHz (89 watts) $92 (free s/h @ NE)

I've got 4GB (1gb x 4) of OCZ Platinum Revision 2 PC2-6400 memory rated at 4-4-4-15. My current Asus M2N-E can't run it at it's native speed, so it has to slow it down and run at CL5 unfortunately. If I get a new motherboard, I need to make sure it is compatible with this memory so I can run it at CL4.

The 5400 will run at 800FSB but the 5600 and 6000 won't unless I overclock the memory settings in the bios. I do ocassional video encoding (xvid to dvd, etc) as well as gaming on my box. I do other tasks that are both cpu and hard drive intensive as well.

Which processor should I get? It seems to me having a 5400 running at 800FSB will be better (even a little bit) than a 5600 (only 100mhz faster) running under par, FSB wise as I won't overclock my box.

Just as a side note, my current X2 3800 runs in the 30's celcius (idle) during the winter and in the 40's celcius idle during the summer. That iswith a fan blowing into the case. I always have problems keeping my office cool which is why I need an external fan blowing in the case with the panel off. I'm not sure how much hotter an 89watt processor will run, over a 65watt one such as mine. The last thing I need is meltdown, hahaha.

Any additional suggestions? Thanks to all for the input and debate on this issue.

-- MaSoP
a c 134 à CPUs
a b } Memory
October 29, 2008 8:53:14 PM

Based off of wisecrackers post, I'd get the 5600+. Do the overclock like he said, and you have a 3.2GHz dual core CPU running 800MHz ram, for $83 from ZZF.

As a side note, because the memory controller is on the CPU, your motherboard shouldn't play into the OCZ's timings. Double check your ram, it might not run at 4-4-4-15 unless you bump the voltage up to 2.0-2.2. Most memory that runs with 4 timings needs more voltage. Your system might have defaulted to Jadec standard of 1.8, in which case the memory can only do 5s.
October 29, 2008 11:08:56 PM

Get the 5400+ BE, $77 and FS at newegg. Of course, that's without a heatsink and fan. But I always buy aftermarket coolers because I always overclock.
a b à CPUs
October 30, 2008 4:39:50 AM

4745454b said:
Based off of wisecrackers post, I'd get the 5600+. Do the overclock like he said, and you have a 3.2GHz dual core CPU running 800MHz ram, for $83 from ZZF.

As a side note, because the memory controller is on the CPU, your motherboard shouldn't play into the OCZ's timings. Double check your ram, it might not run at 4-4-4-15 unless you bump the voltage up to 2.0-2.2. Most memory that runs with 4 timings needs more voltage. Your system might have defaulted to Jadec standard of 1.8, in which case the memory can only do 5s.


Pretty much anything higher than 2.6Ghz ~ ish and with 2MB L2 (ie Windsor) will do you well... You can always OC to about 3GHz ~ ish with something higher than 2.6GHz, heck I got to 3.3Ghz stable with my BE-2400! (hit HT wall =P)
October 30, 2008 3:29:06 PM

4745454b said:
Based off of wisecrackers post, I'd get the 5600+. Do the overclock like he said, and you have a 3.2GHz dual core CPU running 800MHz ram, for $83 from ZZF.

As a side note, because the memory controller is on the CPU, your motherboard shouldn't play into the OCZ's timings. Double check your ram, it might not run at 4-4-4-15 unless you bump the voltage up to 2.0-2.2. Most memory that runs with 4 timings needs more voltage. Your system might have defaulted to Jadec standard of 1.8, in which case the memory can only do 5s.


Unfortunately my existing motherboard (M2N-E) cannot go above 1.95v which is why the memory is stuck running at cl5. I'll need a newer motherboard that supports as high as 2.3v in order to fully utilize the memory. What a pain! Now to find a solid ($150 or less)
AM2+ board to include with that 5600+ cpu. :-) Thanks!

-- MaSoP
a c 217 à CPUs
a b } Memory
October 30, 2008 5:59:02 PM

masop said:
Unfortunately my existing motherboard (M2N-E) cannot go above 1.95v which is why the memory is stuck running at cl5. I'll need a newer motherboard that supports as high as 2.3v in order to fully utilize the memory. What a pain! Now to find a solid ($150 or less) AM2+ board to include with that 5600+ cpu. :-) Thanks!

-- MaSoP


If you are an Asus kinda guy:

ASUS M3A78 AM2+/AM2 AMD 770: $90
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

or

ASUS M3A78-T AM2+/AM2 AMD 790GX: $160
http://www.newegg.com/Product/Product.aspx?Item=N82E168...


Best lookin' deals ...

GIGABYTE GA-MA790GP-DS4H AM2+/AM2 AMD 790GX: $138
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

or

Foxconn A7DA-S AM2+/AM2 AMD 790GX: $110 AR
http://www.newegg.com/Product/Product.aspx?Item=N82E168...


If you are looking to the future and want your best possible performance snag a model with sb750 (the Asus M3A78 is sb700).
October 31, 2008 1:20:18 PM

Wisecracker said:
If you are an Asus kinda guy:

ASUS M3A78 AM2+/AM2 AMD 770: $90
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

or

ASUS M3A78-T AM2+/AM2 AMD 790GX: $160
http://www.newegg.com/Product/Product.aspx?Item=N82E168...


Best lookin' deals ...

GIGABYTE GA-MA790GP-DS4H AM2+/AM2 AMD 790GX: $138
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

or

Foxconn A7DA-S AM2+/AM2 AMD 790GX: $110 AR
http://www.newegg.com/Product/Product.aspx?Item=N82E168...


If you are looking to the future and want your best possible performance snag a model with sb750 (the Asus M3A78 is sb700).


Well, after doing further research, this is the conclusion I've come to:

Only the following boards meet the minimum specs I need, including dual x16 support for crossfire (no 4x/8x/16x mix non-sense):

asus m3a79-t deluxe - $189 (newegg)
dfi lanparty dk-790fxb-m2rs $??? (who sells this model?)
dfi lanparty dk-790fxb-m2rsh - $175 (newegg)
gigabyte ga-ma790fx-dq6 (rev 1.0) $??? (who sells this model?)
msi k9a2 platinum - $150 (newegg)

I've been unable to find other boards that have the following base specs:

6 sata ports
4 memory slots
dual pci-e 2.0 x16 slots (allowing true x16/x16 crossfire)

It seems that only the 790FX chipset can really handle a true crossfire setup. I don't think it is worth the savings to get a cheaper board and run crossfire at 4x or 8x mode. That is too much of a bottleneck for higher end graphics cards. I plan on moving to dx10 sometime down the road, so I don't want to hamper my upgradability by creating such a bottleneck in my system. With all of that in mind, I am looking at having to spend $150-$200 for a motherboard; not $100 or less like I was hoping. Thanks for the input!

-- MaSoP
a c 134 à CPUs
a b } Memory
October 31, 2008 1:42:43 PM

How does this board fail?

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

7 SATA ports, 4 memory slots, and 2 PCIe 2 16x slots. It has the 780G chipset, I suspect there are 780/790 boards that will do what you want. 790FX is expensive, so keep looking. Keep in mind that each PCIe 2 lane has 500Mbps of transfer speed, so 8x + 8x (PCIe 2) = 16x + 16x (PCIe 1). Bandwidth speaking at least.
a c 217 à CPUs
a b } Memory
October 31, 2008 3:32:03 PM

I think you are at the point where you need to look at your overall budget and decide what will be best for you now - and in the future.

If I had the cash I'd be all over the Asus M3A79-T Deluxe 790fx with sb750.

But you will have to judge if it's worth $40 more to you than the Asus 790gx (which I think has 6 SATAs - one just happens to be an eSATA port) or the $90 difference with the Foxconn 790gx.

That cash could go towards a 1Gb HD4870 or a HD4850 Crossfire - or save it towards a 45nm Denab Phenom.

Here is the THG article on ""How Does PCI Express 2.0 Scale? ""
http://www.tomshardware.com/reviews/pci-express-2-0,191...

And I think that Jetway mobo is one heck of a deal - but it's got sb600, not sb750. That would be my concern more so than a PCIe Gen2 x8x8 Crossfire (but I'm wacky that way ....)
October 31, 2008 4:02:52 PM

The 790FX boards are the only chipset with that you're looking for, as I've researched this same situation for a while now. You want the 790FX northbridge paired with the SB750 southbridge. 790GX boards only run one PCI-E 2.0 16x at a time, as the second PCI-E 2.0 slot will automatically be throttled to 8x. We're just now entering the stage in video cards where 8x can throttle performance in the higher end cards. Personally, I'd spend ~$200 for a 790FX/SB750 board and get a decent priced dual core, like the 5400+ BE for $77 on newegg, and upgrade to Deneb in the somewhat near future when prices start to drop a bit.