DDR confusion...

  • Thread starter Thread starter Steven Yockey
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Steven Yockey

Ok, over the weekend I upgraded from a Intel 815e chipset motherboard
with a P3 to a VIA PT880 chipset with a Celeron D. I am now in the world
of DDR, quad pumping, timing ratios, etc. I know this is not a fast
processor but it's considerably faster than my old setup and I do have
some room to grow now.

I'm confused a little though. I have read that it is better to have your
memory running synchronous with your CPU/FSB. I bought PC3200 memory
thinking that I would someday be buying a 800FSB P4. So I have a CPU
using a system clock of 133mhz and memory designed for a 200mhz system
clock, ie. not synchronous. This is exactly how my motherboard (Abit
VT7) has it set up and it works fine. I was curious though about if it
would be a little faster if I ran it at 133, so I changed it in the
BIOS. No Post! As a matter of fact it was a little dodgey getting back
into the BIOS setup to change it back. I changed it back and all was
well. The memory is not the cheapest memory (Corsair Valueram) but not
top notch either, I figured there would be no problem running slower.
Motherboard issue? Memory issue?

I'm pretty happy for the moment with how it runs, but I like to have my
PC running up to it's full potential. I would like to know why I can't
run at a DDR266 speed.

TIA
 
Ok, over the weekend I upgraded from a Intel 815e chipset motherboard
with a P3 to a VIA PT880 chipset with a Celeron D. I am now in the world
of DDR, quad pumping, timing ratios, etc. I know this is not a fast
processor but it's considerably faster than my old setup and I do have
some room to grow now.

I'm confused a little though. I have read that it is better to have your
memory running synchronous with your CPU/FSB.
Click to expand...

Sometimes, particularly on Socket A Athlons. They ran the
FSB at a DDR rate though, your board doesn't... making a
higher memory bus a bit of a benefit, even moreso if you
were running integrated video.
I bought PC3200 memory
thinking that I would someday be buying a 800FSB P4. So I have a CPU
using a system clock of 133mhz and memory designed for a 200mhz system
clock, ie. not synchronous. This is exactly how my motherboard (Abit
VT7) has it set up and it works fine. I was curious though about if it
would be a little faster if I ran it at 133, so I changed it in the
BIOS. No Post!
Click to expand...

Well that's odd, could be a bios bug or perhaps by
downclocking it you left the memory timings in "auto" mode
so it reduced the timings automatically with the manual bus
speed change (as most memory IS SPD programmed to have lower
[faster] timings at lower bus speed), ultimately resulting
in a motherboard-memory-timing combination that wasn't even
stable enough to POST. You could retry it with memory
timings manually locked at something like 2.5,3,3,4, but
personally I'd just leave it at asynchronous +33 speed.
As a matter of fact it was a little dodgey getting back
into the BIOS setup to change it back. I changed it back and all was
well. The memory is not the cheapest memory (Corsair Valueram) but not
top notch either, I figured there would be no problem running slower.
Motherboard issue? Memory issue?
Click to expand...

See above
I'm pretty happy for the moment with how it runs, but I like to have my
PC running up to it's full potential. I would like to know why I can't
run at a DDR266 speed.
Click to expand...

The largest benefit you would have is overclocking the CPU
by raising the FSB a little, but of course that also entails
(re?)testing CPU and memory stability... and possibly a CPU
voltage increase beyond a certain point. Many Celerons
though, have a lot of headroom in them for overclocking,
especially with the lower FSB spec they aren't even putting
modern motherboards above normally expected range.
 
I have a CPU using a system clock of 133mhz and memory designed for a
200mhz system clock, ie. not synchronous. This is exactly how my
motherboard (Abit VT7) has it set up and it works fine. I was curious
though about if it would be a little faster if I ran it at 133, so I
changed it in the BIOS. No Post!
Click to expand...

If you double the data rate of 133MHz you get 266 (DDR266 = 133MHz). Your
memory is rated DDR400 (PC3200), then its maximum speed is 200MHz. You said
your FSB is set to 133MHz, so I don't understand why you tried to run it
faster at 133MHz - its already doing that speed?!?

I would like to know why I can't run at a DDR266 speed.
Click to expand...

You already are! 133Mhz is DDR266 speed.
 
GT said:
If you double the data rate of 133MHz you get 266 (DDR266 = 133MHz). Your
memory is rated DDR400 (PC3200), then its maximum speed is 200MHz. You said
your FSB is set to 133MHz, so I don't understand why you tried to run it
faster at 133MHz - its already doing that speed?!?




You already are! 133Mhz is DDR266 speed.
Click to expand...
No, the memory is running at 200 or DDR400. CPUZ reports it as FSB+66.
After looking at one of my son's computer with CPUZ and seeing what is
reported under the SPD timings I think I may know what the problem is.
My memory only has SPD timings for 200, so when I change it to 133 and
leave the DRAM timings on AUTO, it doesn't know what to do. Sounds
reasonable anyway.
 
kony said:
Ok, over the weekend I upgraded from a Intel 815e chipset motherboard
with a P3 to a VIA PT880 chipset with a Celeron D. I am now in the world
of DDR, quad pumping, timing ratios, etc. I know this is not a fast
processor but it's considerably faster than my old setup and I do have
some room to grow now.

I'm confused a little though. I have read that it is better to have your
memory running synchronous with your CPU/FSB.
Click to expand...


Sometimes, particularly on Socket A Athlons. They ran the
FSB at a DDR rate though, your board doesn't... making a
higher memory bus a bit of a benefit, even moreso if you
were running integrated video.

I bought PC3200 memory
thinking that I would someday be buying a 800FSB P4. So I have a CPU
using a system clock of 133mhz and memory designed for a 200mhz system
clock, ie. not synchronous. This is exactly how my motherboard (Abit
VT7) has it set up and it works fine. I was curious though about if it
would be a little faster if I ran it at 133, so I changed it in the
BIOS. No Post!
Click to expand...


Well that's odd, could be a bios bug or perhaps by
downclocking it you left the memory timings in "auto" mode
so it reduced the timings automatically with the manual bus
speed change (as most memory IS SPD programmed to have lower
[faster] timings at lower bus speed), ultimately resulting
in a motherboard-memory-timing combination that wasn't even
stable enough to POST. You could retry it with memory
timings manually locked at something like 2.5,3,3,4, but
personally I'd just leave it at asynchronous +33 speed.
Click to expand...
I think you have hit on it. With CPUZ on my son's computer, it reports
SPD timings for 133 & 166. My memory only reports one set of timings; 200.
 
No, the memory is running at 200 or DDR400. CPUZ reports it as FSB+66.
After looking at one of my son's computer with CPUZ and seeing what is
reported under the SPD timings I think I may know what the problem is.
My memory only has SPD timings for 200, so when I change it to 133 and
leave the DRAM timings on AUTO, it doesn't know what to do. Sounds
reasonable anyway.
Click to expand...

Well it knows what it is programmed to do, just that what
it's programmed to do isn't retaining stability in this
scenario. Typical PC3200 memory is programmed not just with
timings for 200MHz bus rate but also at least one or two
speed steps lower... but typically it does lower the timings
which 'can' be a valid thing to do but only in concept, in
practice a board may not be stable at the lower timings with
any particular module.
 
Steven Yockey said:
No, the memory is running at 200 or DDR400. CPUZ reports it as FSB+66.
After looking at one of my son's computer with CPUZ and seeing what is
reported under the SPD timings I think I may know what the problem is. My
memory only has SPD timings for 200, so when I change it to 133 and leave
the DRAM timings on AUTO, it doesn't know what to do. Sounds reasonable
anyway.
Click to expand...

So can you find out the timings at 200MHz, then change the frequency and
manually set the figures yourself. I'm still not sure why you want to slow
your memory down - the faster the better I would say (unless it is
overheating).
 
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