nF4 Memory Advice (updated 14/11/06)

[Sharp]

Using memory modules rated higher than PC3200

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When buying/choosing memory modules, you may have come across modules rated higher than PC3200, e.g. PC3500/PC3700/PC4000/PC4200/PC4400/PC4800/PC5000

 

These modules are rated higher as they can operate at a higher frequency. A higher frequency module can handle more data in one go, which means it has a greater data bandwidth.

 

The number after the letters PC = the data rate, e.g.

 

# PC3200 = 3200MB/s, operational frequency = 200Mhz (400DDR)

 

# PC4000 = 4000MB/s, operational frequency = 250Mhz (500DDR)

 

# PC4800 = 4800MB/s, operational frequency = 300Mhz (600DDR)

 

More MB/s (Megabytes per second) is faster but if you buy a module rated more than PC3200 it will not make your pc any faster, in fact it has the ability to make things slower.

 

So what is the point of buying a module rated more than PC3200?

To explain this you need to know how the memory gets filled with Data.

 

 

The basic understanding

(An AMD Athlon XP3200+ Barton 2.2Ghz 200Mhz FSB 32bit CPU)

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Ask yourself, what is controlling the data flow and how is data sent to the memory?

The answer: the CPU is and it sends data along the FSB. (Front Side Bus)

 

# The CPU FSB = 200Mhz (400DDR)

 

# CPU FSB of 200Mhz with DDR = capable of 3200MB/s transfer rate. (just like the memory rating, PC3200).

 

# The memory is only used as a storage space.

 

# It does not process anything.

 

# The CPU sends/retrieves data to/from the memory. (Transfers)

 

If the CPU FSB frequency is only 200Mhz with DDR, how much data can it send?

You should be thinking 3200MB/s.

 

So what good is PC4000 if your CPU can only transfer 3200MB/s?

 

From the above, you should see that for our AMD XP3200+ Barton CPU,

It is the CPU FSB frequency that determines the maximum Data rate/Bandwidth.

[

Remember this

]

 

 

Why having the memory run over 200Mhz will not increase performance

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If you understand what was said above then this should make sense, think of it like this,

 

# Your water supplier sends you water at a rate of 50 litres per second.

 

# When the water gets to your house you have an accelerator on your tap that makes it travel at 100 litres per second into a bottle.

 

If you open your tap and count to 1, how much water will you have in your bottle?

The answer is 50 litres not 100.

 

In that example,

Water supplier = CPU

Tap with accelerator = Memory

Count to 1 = Benchmark

 

And if the tap accelerator was only 25 litres per second it would be a decrease in flow rate, chokes system performance. Now you should see why operating the memory above the CPU FSB frequency has very little effect.

 

 

What about the AMD 64bit CPUs?

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The rule still applies but a few things are different.

In both 64bit & 32bit platforms the system architecture is,

 

CPU <---> Memory controller <---> Memory

 

# CPU talks to Memory controller

 

# Memory controller talks to Memory

 

But the main difference in the 64bit platform,

# The memory controller is now integrated inside the CPU core.

 

This means that the data rate between the CPU and Memory controller is not limited by the FSB frequency.

 

 

 

The 32bit CPU FSB limitation explained

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On the 32bit platform, the Memory controller was on the motherboard in the northbridge chip.

 

# The CPU plugged into the board.

 

# CPU communicated to the Northbride along the FSB. (1 in the diagram)

 

# Northbridge (with Memory controller inside it) communicates to the memory plugged in the board. (2 in the diagram)

 

# So the CPU to Northbridge (with memory controller inside it) data rate = limited by the FSB frequency.

 

Therefore the maximum Memory data rate = determined by the CPU FSB, as the Memory controller can only transfer what it gets from the CPU.

 

 

 

By removing the memory controller from the Northbridge and placing it directly inside the CPU core, The CPU to Memory controller data rate is no longer restricted by the FSB frequency.

 

So now the Memory controller is running at the same speed as the CPU core which means it can transfer a lot more data.

 

If you look back at the AMD 32bit platform which was limited to 3200MB/s, you should see why Dual channel mode did not double the memory performance. The Memory controller was limited to a maximum transfer rate of 3200MB/s, the FSB frequency.

 

 

How much data can the 64bit 939 CPU transfer to the Memory controller?

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It is a lot of data and it depends on the CPU frequency. As everything inside the core runs at the CPU operating frequency, a 2Ghz CPU will be able to send more data to the Memory controller than a 1.8Ghz CPU. With the old 32bit CPUs the operating frequency did not have as much of an impact on the memory performance. (Due to the FSB limitation).

 

Now the actual theoretical data rate from CPU <---> Memory = 6400MB/s so dual channel mode is going to make a difference. I should also mention that the memory modules you plug into the board are connected directly to the CPU's Memory controller. (As shown in the AMD 64bit system diagram)

 

Due to efficiency/latencies, the actual data rate is not 6400MB/s but close and it gets closer as the CPUs operating frequency increases.

 

Overclocking the CPU to 250Mhz FSB (Memory Controller to Memory BUS) can push the data rate beyond 6400MB/s and into the 7000MB/s - 8000MB/s range, very fast and you would need PC4000 memory modules, I think it's time to answer that question.

 

 

What is the point of buying a module rated more than PC3200?

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Having reached this point, you should understand that the Maximum Memory data bandwidth possible depends on the CPU FSB frequency or in the AMD 64bit CPUs, the Memory controller to Memory link (BUS) frequency.

 

And also that using memory rated above 200Mhz (e.g. XXXMhz) is not going to make your PC perform faster unless the Memory controller to Memory frequency is also at XXXMhz and the CPU can generate that amount of data.

[

Very Important

]

 

# PC4800, 300Mhz (600DDR) = capable of handling 4800MB/s

 

# PC4800, 300Mhz (600DDR) in dual channel mode = capable of handling 9600MB/s

 

9600MB/s is a lot of data and it would take a very powerful CPU to generate/transfer that amount of data to the memory.

 

All the AMD 64bit CPUs have a Memory controller to Memory BUS frequency of 200Mhz (400DDR) and run in Dual channel mode, (Capable of transferring 6400MB/s). So why would you want PC4000 memory modules?

 

Manufacturers offer PC4000 as it allows to the user to overclock their CPU FSB to 250Mhz without worrying about the memory not being able to run at 250Mhz. e.g. Suppose you had PC3200 and overclocked the CPU FSB to 250Mhz

 

# In order to make the most out of the overclock you will need the memory to run at 250Mhz, to handle the data rate. (Overclocking increases CPU performance = increased data rate between memory and CPU = exceed 6400MB/s)

 

# Increasing the memory frequency = Allows it to handle more data

 

# But overclocking PC3200 to 250Mhz may not work. (Does now on most good modules)

 

# So manufacturers came up with PC4000, modules that will do 250Mhz (not overclocking them).

 

And this allows you to get the most out of your overclock, nothing will be limiting the data transfer rate from the Memory controller to the Memory.

So PC4000 memory modules or above are for people that wish to overclock

.

 

You can also use PC4000 and run it at PC3200, 200Mhz instead of 250Mhz, (underclocking). All boards that support PC3200, support PC4000 or above but the key point, running PC4000 to its full potential means you must overclock your CPU. And by default all manufacturers do not support overclocking as it can cause damage.

 

One day when the CPUs get faster, the default Memory controller to Memory frequency may increase to 250Mhz and PC4000 may become the next standard (not for overclockers), Maybe

 

Conclusion

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I hope you have enjoyed reading and if you are still a bit confused don't worry, it will make more sense over time as your computer knowledge increases, Have fun,

 

*+*Sharp+*+

16/10/05

[Guest Blooz1]

Good basic explanation, Sharp!

 

The water analogy is a good one, people can relate to that! Pics would be great!

 

There's one place where I think you should add something;

 

(quote:)

"So it is the CPU that determines the bandwidth/Data rate."

 

(In 32-bit section..)

 

I think you should insert "FSB" after CPU - YOU know what you mean, and I know what you mean, but that's not quite what it says - as is, it could be taken wrong.

 

(Just a minor point - but it could cause confusion to someone who doesn't understand the concepts.)

[Sharp]

How did I miss that.

[Guest Blooz1]

Hey, it's easy! You were thinkin' ahead of what you were typing! I do it all the time!

 

Just trying to help...

[Neoki]

What about the crucial ballsitix tracer 2gb i got that and want to know my limits

[Sharp]

Hello,

 

Micron 5B-D chips = ~280Mhz.

 

Overclocking results vary so expect it to be lower.

[Ivan OS]

What about Corsair Twinx 1024 3200c2 v1.5?

I think they use Winbond Utt BH-5.

I`am having problems with compability with my board, so now i use Geil ONE TCCD but from your experience what about my Corsair ram`s?

Thanks!

[Sharp]

Hello,

 

Something about corsair that makes it a problem in the DFI nf4 board, a lot of people can't get it to work.

 

That's why Corsair is not on the list

 

What timings were you trying with the Corsair modules? (yeah they are UTT BH-5).

[Ivan OS]

Hello,

 

Something about corsair that makes it a problem in the DFI nf4 board, a lot of people can't get it to work.

 

That's why Corsair is not on the list

 

What timings were you trying with the Corsair modules? (yeah they are UTT BH-5).

Stable (that`s relative term for me and that memory)overclocked at 245mhz 2-3-3-6 1T.

I managed sometimes at 2-2-2-8-10-14-2-2-1-2-3120-auto-en-auto-o-8-l1-8-5-128-disable-16x-7x-disable

[Goltnor]

Hello Sharp, hey an error is here:

 

- OCZ EL DDR PC-4000 Gold Edition [2x1GB] (Samsung UCCC[/color]) [3-4-4-8]

 

- OCZ EL DDR PC-3200 Platinum [2x1GB] (??[/color]) [2-3-2-5]

Part number: OCZ4002048ELDCPE-K

http://www.ocztechnology.com/produc...hannel_platinum

 

Greetings

[Sharp]

I didn't know what colour to use so I left a ??.

I put it as lime green to show that it is a Samsung chip.

[Deus Mortem]

I'm getting these for my first build (With DFI LP nF4 Ultra-D) and I'm wondering whether these'll work fine.

 

http://www.newegg.com/Product/Product.asp?...N82E16820145449