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Old 09-28-2005, 02:05 AM   #1 (permalink)
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Default Figuring out Memory speeds vs FSB speeds

Aight,

I have been trying to figure this out for months. I have not been doing much or keeping up on the computer field of my life for a couple years but I am trying to get back into it since its something I have fun with.

But im getting agrivated already! lol

Im trying to find out what memory type (DDR333, DDR400 etc.) I need and why.

I was looking at MSI motherboards and the have a board that is capable of seeing a FSB of 1 Ghz, 2000 MT/s. Now this is where I get confused. I dont even know how to word my question.

For some background on a motherboard with this FSB
http://www.msicomputer.com/product/p...tinum&class=mb

How can I figure out what speed of RAM I need? If I have a MB with 1ghz FSB. I figure I would need 4 DDR500 Chips on a dual channel to equal the 16000MB/s Transfer rate you would see with a 1ghz FSB.

My Math

1000 (1ghz FSB) x 2 (Cycles per clock) = 2000 (MT/s)
2000 (MT/s) x 8 (Bus Width) = 16000 (MB/s transfer rate).

so with this math. Would I need 2 pairs of DDR500 runnign dual channel to reach the 16000 MB/s transfer rate (bandwidth)?

500 x 8 = 4000
4000 x 2 = 8000 MB/s (2 DDR500 chips running 2 channel)

8000 x 2 = 16000 MB/s (4 DDR500 chips running 2 channel)

MSI boards only go up too DDR400 which in my math world would only equal to a total bandwidth of 12800 MB/s. Seems slower then the total Bandwidth capable of the motherboard.

Am I thinking totally backwards or to far to the left ? I know im not thinking something right.

Now with the Intel 800mhz FSB. Most (if not all?) Motherboards used dual channel DDR. So they would use 2 DDR400 to equal the 6400 MB/s transfer rate you would see with the 800mhz FSB.

800 x 8 = 6400 MB/s

DDR400 = 3200 MB/s

3200 x 2 = 6400 MB/s (Pair of DDR400 running Dual Channel)

NOW, I am so confused its not even funny. Im reading the Upgrading and Repairing PCs book by Scott Mullers 16th Edition and its not adding up. Page 472 is confusing me when I put it into the real world.

Like I said. I dont even know how to word my question and the answer is probubly alot easier then im making it to be. Can someone fill me in?

Tell me how im supposed to figure this out?

Thanks alot guys/girls

Justin -
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Old 09-28-2005, 02:30 AM   #2 (permalink)
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Aight. So I found out there is now ddr500. only DDR2-500. Anyways. It seems all motherboards, ASUS, MSI, ABIT and others. Are saying the boards produce speeds up too 2000 MT/s but there is no memory combination in DDR1 format that can go that fast. Am I wrong?
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Old 09-28-2005, 07:20 AM   #3 (permalink)
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you need DDR400 pc3200. is what your board supports. you can get DDR500 and the board will underclock your cpu then you can put your FSB to 250 and then you will start the real OCing. DDR2 is not supportred. and they go all the way up to DDR600 btw.
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Old 09-28-2005, 09:32 AM   #4 (permalink)
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What PZEROFGH said. You're making it more complicated for yourself than it need be .

Regarding the S939 setup you're looking at: All AMD64/FX/X2's have an external frequency of 200MHz (by default). Thus, all S754/939 boards have a default CPU bus of 200MHz. Thus, you need at least DDR400 (@200MHz Double Data Rate) to support the CPU/mobo.
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Old 09-28-2005, 01:18 PM   #5 (permalink)
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Ok....HM.

I think the specs on the mobo(meaning motherboard right?) when they say 2000mt/s (or mhz?) that is the total bandwidth(FSB) of the board.

So..

If there is an external clock speed of 200mhz. And you slap in a DDR400, just one, you are now add 400mhz? Then if you have 2 of them on dual channel you will now have 800 mhz? FSB?
If you then add 2 more DDR400 on dual channel would that bring the FSB to 1600mhz?

Quote:
you can get DDR500 and the board will underclock your cpu then you can put your FSB to 250 and then you will start the real OCing.
What do you mean about "underclocking" the CPU?

Thanks for the help guys, Not keeping up on this stuff was a bad idea especially with a bad memory.
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Old 09-28-2005, 05:02 PM   #6 (permalink)
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You're totally off on the Memory stuff.

OK, the motherboard (hopefully) supports DDR400 memory. DDR400 memory runs at 200MHz.

Most of the newer AMD systems have the FSB Integrated onto the microprocessor.

As you know, the CPU speed (2000Mhz or 2.0GHz for example) is determined by the FSB times the CPU Multiplier. For Socket 939 AMD Cpus, the FSB is set to 200Mhz by default. The FSB is what the resy of your system will revolve around. In the case of the 2000Mhz or 2.0Ghz CPU, the 2GHz is determined by th FSB running at 200Mhz, and the multiplier being set at 10x. 200Mhz x 10 = 2000Mhz (2.0GHz).

As for memory. Memory runs at the same speed as your FSB (unless you set a divider, but thats a topic for another day, and not really important to you). No matter how many modules of DDR400 memory you have, they will ALL run at 200Mhz each and will not be added, so no 200+200+200+200=800. No, thats not what happens. If you have 4 modules of 256MB DDR400 memory, then it will be 1GB of memory running at 200MHz.

The 1000Mhz that you see for the motherboard is the supported HyperTransport Bus speed. The HyperTransport Bus is for AMD systems like the FSB (Front Side Bus) is for Intel Systems. You shouldn't worry about the HyperTransport Bus speed too much. Don't focus on it.

If you didn't know all that, I suggest you don't build your own PC.
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Old 09-28-2005, 05:04 PM   #7 (permalink)
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Quote:
Originally posted by viperdude152
What do you mean about "underclocking" the CPU?
PZERO misworded that. If you buy DDR500 memory, it will be running at 250 MHz. But your motherboard (and no other AMD motherboard) supports a speed higher than 200MHz. That means that the DDR500 memory will be underclocked (or have its clock speed reduced) to 200Mhz (DDR400). Note: Nothing will happen to the CPU.

DDR500 Memory is only used for/goof for overclocking, which is something you shouldn't worry about since you're VERY far behind today's technology.
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Old 09-28-2005, 05:10 PM   #8 (permalink)
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Yeah, it gets a bit complicated with AMD64s since there is technically no FSB since the memory controller in built onto the chip itself

Quote:
No matter how many modules of DDR400 memory you have, they will ALL run at 200Mhz each and will not be added, so no 200+200+200+200=800. No, thats not what happens. If you have 4 modules of 256MB DDR400 memory, then it will be 1GB of memory running at 200MHz.
Depends on the memory controller, for example pre-RevE Athlons would underclock memory to 333MHz if you tried to use all four slots
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Old 09-28-2005, 05:28 PM   #9 (permalink)
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Quote:
Originally posted by gaara
Depends on the memory controller, for example pre-RevE Athlons would underclock memory to 333MHz if you tried to use all four slots
Yup, like my Clawhammer does. Once you manually set the memory frequency in BIOS though (hence the memory divider @ 1:1), you shoudn't have any problems.
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Old 09-28-2005, 06:26 PM   #10 (permalink)
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Quote:
Originally posted by gaara
Depends on the memory controller, for example pre-RevE Athlons would underclock memory to 333MHz if you tried to use all four slots
Crap, I forgot about that, lol. Well, I was trying to explain it to him and I guess it just slipped my mind. But then again, no one would really buy a pre-RevE A64 today anyways.
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