Memory v.s. Processor speed (Athlon 64x2)

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Can someone explain 64x2 processor and memory speed combinations.   Is it
correct to assume any 64x2 processor speed will work with any memory speed
except at possibly reduced efficiency?  What are the max processor speeds
what till run with each of the following DDR-800, DDR-667, and DDR -533?

Re: Memory v.s. Processor speed (Athlon 64x2)

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On a good AM2 motherboard, CPU frequency and memory frequency are separate
issues, and can be controlled individually. Having slower memory will slow
your system a bit, but you can use any X2 CPU with any of the DDR2 speeds
you've listed. My Asus M2N-E allows me to set CPU frequency to anything
between 200 (stock) up to 400, and separately, I set memory clock frequency
to anything between DDR2-400 to DDR2-800.
You would need to check out the BIOS features of the motherboard you want to
see if it allows the same degree of control.

Oh, one other thing. DDR2 memory is cheap right now, so I'd advise getting
good quality DDR2-800 to get best overall performance.

Re: Memory v.s. Processor speed (Athlon 64x2)

Don't forget that when you increase the clock speed up from 200, the
memory speed increases proportionately, so if your memory won't
overclock you'd set it to a lower speed and calculate how high the clock
could go before you'd have to set it to a still lower speed because it
had come back up to its stock speed.

For instance, on my old nforce 3 with DDR 400, I overclocked it from
clock 200 to 240, 20%. So, when I set the memory to 333 (same as 166),
it came back up to 400.

However, there's the timing issue. The motherboard sees that the memory
is set to a slower speed, so it decides to tighten up the timings. Then
when the memory actually comes back up to a normal speed, the timings
may be too tight and cause errors. To avoid that I start out stock with
the memory the way it's meant to be and lock the timings by going to
manual timings. Then they shouldn't change any more, but I write down
the numbers and check them later.

Ed Light

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Re: Memory v.s. Processor speed (Athlon 64x2)

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Hi, Ed.
While what you say about the memory speed increasing with clock speed is
true with some chipsets (I believe my NFORCE 4 board acts as you describe,
and I know my Asus P5B-Plus does). I don't think it's true of my Asus M2N-E
(NFORCE 580 chipset). With the 580, I get the behavior you describe if I set
memory speed to Auto, but if I select a specific memory speed, that
decouples the memory speed from the clock speed and allows me to set my
clock at 240 and not affect memory speed. When I run tests on the M2N-E PC,
using SiSoft Sandra, it shows the memory at the manually set speed despite
the clock speed increase. On my P5B-Plus, Sandra shows an increased memory
speed proportional to clock speed increases as the chipset on that board
will not decouple the memory clock.

Re: Memory v.s. Processor speed (Athlon 64x2)

OK, Peter. I'll be watching the thread.
Ed Light

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Re: Memory v.s. Processor speed (Athlon 64x2)

I think ram speeds are address by the Front side bus speed.
something about diveded by four to get your ram speed??  Any gurus in
this area?
I want to get a AMD k2 6000, and am having trouble trying to find the
correct information for the recomended ram speed.

Re: Memory v.s. Processor speed (Athlon 64x2) wrote:
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The processor has the memory controller on it. By means of
clock synthesis logic on the processor, it can generate clocks
suitable for running memory at or close to  DDR2-400, DDR2-533,
DDR2-667, DDR2-800. In other words, you can use any memory you
want. Since DDR2-800 memory is available, you could buy a couple
sticks of that.

People calculate these tables, to demonstrate what the synthesis
logic can do. The idea is, the synthesized clock for the memory,
is at or below the value specified by the user in the BIOS screen.
If you set DDR2-800 in the BIOS screen (with core at nominal speed),
this table is not allowed to set the memory on purpose so it runs
at DDR2-801 or higher. But it can use DDR2-799 if the hardware can
make that value. Overclocking doesn't count in the logic, and
the processor doesn't "know" it is being overclocked - it is

The memory can be used in a couple of ways.

If you set the processor input clock to 200MHz, that is "stock".
If you set the memory interface to "DDR2-800", that is what you get.

Now, let's try a second case. Set the memory controller to DDR2-667,
even though the memory is rated at DDR2-800. Now, increase the processor
input clock to 200 * (800/667) or about 240MHz. That causes the processor
core to be overclocked by 20%. So it runs 20% faster than normal. Now,
what happens to the memory. Well, the memory clock also depends on the
processor input clock. If the processor input clock increases, so
does the memory clock. If the memory was set to 667, and is now going
20% faster than that, that is 667 * 1.20 = 800, and so the memory is
exactly in spec. (I.e. The BIOS says "DDR2-667", but the hardware is really
running at DDR2-800 due to the CPU clock choice.)

In other words, you can turn down the memory setting, turn up the
CPU input clock, overclock the core, and yet the memory is still in

Naturally, all hardware has some interface limits, so buying DDR2-1066
memory might not make sense for an AMD processor. The speed of the
memory you buy, is really a measure of the utility you get from it.
If fast memory only bought you 5% more performance, then spending
an extra $200 to get that performance would be stupid. You'd be
better off buying a more capable processor (whatever that is), and
cheaper memory.

So use a little common sense, and buy what everyone else buys :-)
AM2 is positioned currently, for low to mid range systems, so
laying out hundreds of dollars for special memory makes no sense
at all.

If you take a quick look through the reviews here, I see mention
of people using DDR2-800, and that is what I'd buy.


Re: Memory v.s. Processor speed (Athlon 64x2)

On Sun, 22 Jul 2007 04:22:25 -0700, vyaw2003 wrote:

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In addition to Pauls very excellent reply, remember that memory speed
usually has very little affect on overall system performance since 90% of
all memory accesses are usually serviced by the CPU cache, never even
really bringing the memory speed into play. As a rule I always buy the
fastest with a reasonable price. Right now ddr2-533 and ddr2-667 is about
the same price, with ddr2-800 only being slightly higher. Anything above
that is considerably higher. Ref. Pricewatch. So today I'd get ddr2-667 or
ddr2-800. Of course it's all dirt cheap these days compared to 20 years

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