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Compatible RAM faster than backward compatible RAM?

PostPosted: 2007-05-22 05:13
by tien07
I have 400MHz RAM, but my motherboard only supports up to 333MHz. So my motherboard would automatically underclocks it to 333MHz.

I was told that a 333MHz RAM runs faster and better than an underclocked (to 333MHz) 400MHz RAM. Is this true?

I always thought that it would be the same.

PostPosted: 2007-05-22 08:22
by chrismortimore
The difference is probably negligible.

PostPosted: 2007-05-22 08:32
by sinical
I doubt even a benchmark could tell the diffrence

PostPosted: 2007-05-30 01:56
by swirling_vortex
RAM moves data so fast, the clock speeds don't matter too much unless you need very high performance out of your system. Even then, Linux manages RAM much better than Windows anyway, so I don't think you have anything to worry about.

PostPosted: 2007-05-30 02:31
by diego1116
Probably you was told about sync/async modes and your case seems slightly different. Just found something at
Dealing with Memory Speeds: What is sync / async?

(NOTE: ..Does NOT include the Athlon64/FX. They are alot different when it comes to this ...will be updated shortly).

When the memory frequency runs at the same speed as the FSB, it is said to be running in synchronous operation. When memory and FSB are clocked differently (lower or higher than), it is known to be in asynchronous mode. On both AMD and Intel platforms, the most performance benefits are seen when the FSB frequency of the processor is running synchronously with that memory – Although Intel based systems have a slight exception, this is completely true of all AMD-supporting chipsets. Only Intel chipsets have implemented async modes that have any merit. The async modes in SiS P4 chipsets also work correctly. When looking at the AMD-supporting chipsets async modes are to be avoided like a plague. AMD-supporting chipsets offer less flexibility in this regard due to poorly implemented async modes. Even if it means running our memory clock speed well below the maximum feasible for a given memory, an Athlon XP system will ALWAYS exhibit best performance running the memory in sync with the FSB. Therefore, a 166FSB Athlon XP would run synchronously with DDR333/PC2700 (2*166) and give better performance than running with DDR400/PC3200, despite its numbers being bigger. This does not mean to say that PC3200 isn’t a good idea for 166FSB Athlon XPs. Buying slightly higher-rated memory than needed is a good idea if your intent is to overclock and it also allows you some future upgrade room.

To achieve synchronous operation, there is usually a Memory Frequency or DRAM ratio setting in the bios of your system that will allow you to manipulate the memory speed to a either a percentage of the FSB (i.e. 100%) or a fraction (or ratio) i.e. N/N where N is any integer available to you. If you want to run memory at non 1:1 ratio speeds, motherboards use dividers that create a ratio of [CPU FSB]:[memory frequency] or through the use of percentages of the FSB. However, intrinsically, it is possible to see the problem with this and why synchronous operation is preferable on all PC platforms. If for there is divider, then there is going to be a gap between the time that data is available for the memory, and when the memory is available to accept the data (or vica versa). There will also be a mismatch between the amount of data the CPU can send to the memory and how much the memory can accept from the CPU. This will cause slowdowns as you will be limited by the slowest component.

PostPosted: 2007-06-06 12:30
by tien07
Yes, the sync/async is what I was talking about. But could not have explained it better, because I did not know very much about it or the proper term for it.

I was hoping to get some opinions from experienced users.

So if I have a CPU FSB at 133MHz (266) and my RAM is at 266MHz, would it run more efficient than if it would with a 333MHz or a 400MHz RAM?

PostPosted: 2007-06-09 03:10
by llivv

PostPosted: 2007-06-09 03:48
by DeanLinkous
lots of opinions in this thread.... :P
Now let me offer mine :lol: