Underclock AMD X2 4800/2500?

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Hi - I've done a lot of digging and can't find the answer to this...

I have an AMD X2 65nm 4800 which runs at 2500MHz.
I also have DDR2-6400 800MHz RAM.

Would the system be faster if I used the stock 12.5 multiplier while
the RAM runs at 714MHz, or is it better to drop the multiplier to 12
and let the RAM run at a full 800MHz?

I've found tests which show that the 4600 (2400MHz) outperforms the
4800.  The articles don't explicitly say it, but I gather it is due to
the multiplier.  I'm assuming that simply dropping the multiplier
would make th 4800 run as well as the 4600?  Is it is simple as that,
or is there something I'm missing.

Anyway, my apologies for posting an "underclocking" question.  I don't
like to live dangerously.


Re: Underclock AMD X2 4800/2500?

On Tue, 05 Feb 2008 16:54:50 -0800, wdoe999 wrote:

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The multiplier has no effect on the ram speed. The system bus does. The
normal system bus is 200MHz. And normal ram bus speed for for PC6400 DDR2
ram is 200MHz also. 800MHz is not a real bus speed. It's really a data
rate with DDR2 having a 4:1 data rate. Older DDR PC3200 also has a ram
bus speed of 200MHz, but it only has a data rate of 2:1. Some MB bioses
use the real ram bus speed while others may use the bogus speeds for
settings. Look at your dram settings to determine this.

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I think you've misinterpreted something. An AM2 x2 4800+ will be faster
than an AM2 X2 4600+. Perhaps you're looking at 939 v. AM2 platforms or
possibly CPU's with different L2 cache sizes or different cores.

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That being the case, I'd suggest you leave well enough alone. If you just
have to have more speed. The basics are to lower the HT speed. Lower the
base ram speed. And then increase the system bus speed to increase the
cpu speed. All of my system have X2 3800's in them. I can increase the
system bus from 200 to 233 MHz without any problems thus bringing the cpu
speed up from 2000MHz (10x200) to 2330MHz (10x233), and with monor
adjustments could get them a lot faster. But why? The stock 2000Mhz is
plenty fast enough for my use. In fact I run cpufreq and normally the cpu
speed stays at 1000MHz, only going higher when I stress it. To get max
speed out of a system you'll find yourself screwing with voltages, better
cpu coolers, etc. If you don't know what your doing or have to time learn
by trial and error, forget it. In the end, it won't help that much.

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Re: Underclock AMD X2 4800/2500?

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Your overall system will be faster if left at stock speeds rather
dropping the CPU down to 12x just to get the RAM speed up.  The RAM
speed does not greatly affect the overall speed of the machine.  Or
you could drop down to 12x and increase the FSB to 208 to get you CPU
back to stock speed if you don't want to overclock the CPU but your
RAM would be at 832MHz.  With your CPU at 2500, a comparison between
714 and 832 for your RAM in a benchmark would show almost no
difference in RAM bandwidth with no other changes to RAM settings.
About all that would happen is your latencies would drop very slightly
with the faster RAM clock.  Most BIOS set the command rate to 2T but
you might be able to run your RAM at 1T and that would have an
increase in RAM bandwidth.

To the other guy with the 3800 X2, I ran my 3800 at 2400 (240x10) with
only a minor CPU voltage boost and I set my DDR2-800 to DDR2-666 in
BIOS which with the overclock the RAM was running at 800 again.  With
that overclock my CPU ran about 30C above room temp and in summer the
standard AMD heatsink fan was very noisey when the CPU was at 100%

My board has an nVidia chip-set.  Originally I overclocked using BIOS
which switches off Cool n Quiet for the CPU but I experimented with
nTune and found I could use that to increase the FSB and have CnQ
still working so when the CPU was idle CnQ would drop the CPU down to
1200 (5x240) and drop the CPU voltage as well (CPU was still
overvolted in BIOS).  Win-win for me, I had extra performance when I
needed it and CnQ when I didn't.

Re: Underclock AMD X2 4800/2500?

Wes Newell;526231 Wrote:
> On Tue, 05 Feb 2008 16:54:50 -0800, wdoe999 wrote:
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> speed is
determined by cpu speed divided by the ram divider.  The ram
> divider is
determined by dividing the cpu multiplier by 2.  In this case
> his multiplier
is 12.5 so the ram divider would be 6.25, however you
> cannot use a "broken"
divider so you round up to the next whole number
> which would be 7.  So his ram
speed would be 2500/7*2 or 714 Mhz.
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> reasons for
this.  One is the manufacturing process.  The 4600 processor
> is 90nm and the
4800 is 65nm.  This was one of the first 65nm chips made
> by AMD and they were
still working the kinks out.  The other reason is
> the 4600 has double the L2
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> what
you are suggesting and actually lost performance slightly.  The
> minor decrease
in ram speed does not effect your system in the
> slightest.

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