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Memory Question

By funkyt1111 ·
What is the relationship between the FSB and the memory clock speed?

Example. I have an ASUS P4PE-X mobo. Runs at a 400mhz FSB. In it I have a PC2100 DDR memory module. 512mb worth. PC2100 lists at 266mhz. Since it has DDR technology, does that mean it is actually a 133mhz stick, DDR'd to 266? Or that it will be able to get the stick up to 532mhz with DDR?

In the above example. The processor is a 2.6ghz, P4. Since it is set in the BIOS as a 400mhz FSB, running at 2.6ghz, is it possible to be stressing the memory, or the processor? Is the FSB of the system being dragged down to 266mhz? Thereby degrading the actual FSB of the system and putting stress on it to keep the processer up at that speed?

I know this is an all over the place question, and I'm sorry for that. I'm just trying to understand a problem I'm seeing.
Thanks a ton for any help. -Todd

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by dRb63 In reply to Memory Question

Read the following...


It should answer most of your questions.

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by funkyt1111 In reply to

Thanks for the link. Watch that you don't put unwanted spaces in it. Made for a dead link to start with.

The only thing new I took away from the thread was that the PC2100 memory was only 266mhz, doubled from 133. But that's good to know.

My real problem is geared around the FSB and memory bus not having the same rate. If my mobo is rated at a 400mhz FSB, and my memory can only get to 266mhz. Then will this create issues on a system? Does anyone know how these issues, if any, will manifest?

What is the real benefit to matching your FSB and memory bus rates? Am I looking at a huge performance increase? Or a moderate to low one?
Thanks again. -T

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by TheChas In reply to Memory Question

As to the space that was added to the link, the TR website software adds (and deletes) random spaces to postings.

You have to watch ANY pasted link from a posting for added spaces.

It was a real problem for one site that required a space in the link.

As to your main question, there are so many things going on between the CPU and the various busses that you will not see a significant real world performance gain if you match the CPU FSB and memory speeds.
Benchmark tests are another story. Benchmark scores will show a noticeable gain from having memory that is at least as fast as the FSB.

That said, with the memory running slower than the FSB, you may experience some 'glitches' from time to time, especially if you attempt to tweak the BIOS settings for memory to boost performance. This will be VERY dependant on how well the BIOS and memory controller work with the CPU.

Keep in mind that all the data transfers to the other devices in the PC happen at MUCH slower rates than the FSB.
PCI 66MHz or 33MHz
ISA 5MHz or less
Hard drive 133MB in short bursts.

Now, the more memory intensive your applications are, the more benefit you will see with faster RAM.


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by csmith In reply to Memory Question

The fact that the processor (CPU) is way faster than the memory, and that the Front Side Bus ia faster than the memory, does not create any issues.
It only creates "Wait States" while everbody waits for the transfer from memory.
The heart of question you are asking is: Yes the memory is the speed bottleneck in todays PCs.
Back in the days of the 386 and 486 the processor, bus, and memory all ran at 33 MHz; (Sometimes 25Mhz), but they all ran at the same speed. (Yes, some of the later 486s had internal clock doubling on the CPU chip.)
The problem is that memory speed improvements have not kept up with CPU speed improvements.
Thus, the fastest memory you can use, helps the system the most.
A CPU, waiting for the information to be transfered from memory does not hurt the CPU.
Rather, just the opposite.
The CPU idles while it waits for the memory.
In this state the CPU does no work, uses less power, and actually cools off slightly, because of the lower energy use.
Regards, Chris

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