Different speed on RAM

[Nick]

Hi,
I have a PIII with 2 x 128MB SDRAM PC133. Acquired a 256MB SDRAM DIMM to
double my memory only to discover that it is PC100.

If I install this 3rd DIMM will I have any performance problems (will they
even work?), because of the difference in clock speed? Will the fact that
the RAM will be doubled outweigh any performance loss? Or will I just have
one slow DIMM?

TIA

 

[kony]

Hi,
I have a PIII with 2 x 128MB SDRAM PC133. Acquired a 256MB SDRAM DIMM to
double my memory only to discover that it is PC100.

If I install this 3rd DIMM will I have any performance problems (will they
even work?), because of the difference in clock speed? Will the fact that
the RAM will be doubled outweigh any performance loss? Or will I just have
one slow DIMM?

TIA

Does this P3 have a 133MHz FSB spec or 100MHz FSB spec?

Usually a P3 motherboard will run the memory bus at same speed as the
FSB, or with some later boards, at plus or minus 33MHz to the FSB
speed. Most often it is synchronous to the FSB though, both at same
speed.

If your FSB and memory bus are both at 100MHz, there is no problem.
If your memory bus is at 133MHz, there is POTENTIAL for a problem.
With a 133MHz memory bus, the motherboard will "attempt" to run the
new memory module at 133MHz. If this new module is capable of running
stabily at 133MHz, eveything is fine, but if it can't run stabily at
133MHz, the system might not even POST, or even worse, you could
easily have memory errors.

If this PC100 module is brand new, the odds are good that it can run
at 133MHz stabily, but it certainly can't be assumed. The
motherboard's bios "might" automatically change some memory timing
parameters when it detects another module added, which could be a
slight slowdown in memory access speed, but for the most part the
PC100 memory will not slow down the PC133 memory, any moreso than if
you had installed another PC133 module with the same SPD-programmed
timings, and the motherboard's BIOS is set to use these SPD timings.

Go ahead and try the module unless you're thinking of returning it
while it's still new in box?

BEFORE running the (main) OS at all, first boot to and test the
system for several hours with memtest86:
http://www.memtest86.com


Dave

 

[Nick]

Thanks for the reply.

I do not have a manual for my board and cannot remember the URL for the site
which gives info on most boards.

According to PC Wizard 2004, both banks currently in use are running at
PC100 anyway. FSB is 134 MHz.

Does it matter in which order I put the 3 DIMMs, taking into account speed &
size?

 

[kony]

Thanks for the reply.

I do not have a manual for my board and cannot remember the URL for the site
which gives info on most boards.

Well you can find that out later if you need to.

According to PC Wizard 2004, both banks currently in use are running at
PC100 anyway. FSB is 134 MHz.

That sounds odd, misconfigured. With the FSB at 133MHz, the ONLY
reason the memory should be running at 100MHz is if it had started out
with PC100 memory, which it shouldn't have if running at 133MHz FSB.

On the other hand, I don't know how reliable "PC Wizard 2004" is, or
if "PC100" means anything significant, if it means the modules are
actually running at 100MHz or if that's just the first line of the SPD
setting (after decoded), and the rest was just truncated when
displayed by PC Wizard.

Does it matter in which order I put the 3 DIMMs, taking into account speed &
size?

Some motherboards aren't even stable with 3 memory modules, but only
testing can determine that if someone hasn't already reported this
problem with that specific motherboard. Generally the middle slot(s)
are the worst, I would try the PC100 module in the first slot (nearest
the northbridge and CPU), but you may want to experiment with
slot-locations if Memtest86 shows errors, though if it does show
errors and you're manipulating/storing valuable data, it might be
prudent to keep the PC100 memory out of the system.

Also if the motherboard isn't stable with 3 memory modules you might
try removing one of the 128MB modules and leave the middle memory slot
empty (either "middle" slot if it has 4 slots).

Another way to improve stability might be to go into the BIOS setup
and manually set slower memory timings (larger numbers), but try it
first at "Auto" or "SPD", which should be the same thing, the wording
can vary per motherboard.

I would check the memory bus speed though, it's better to have it
running at 133MHz since the FSB is at 133MHz, if possible.
On the other hand, if PC Wizard had the FSB and memory speeds mixed-up
for some reason, if the FSB was at 100MHz and the memory at 133MHz,
you might consider trying 100MHz for the memory too... keeping both
the same improves performance with a raised speed, or offsets the drop
in performance from a lowered speed, by elminating a buffer put into
use when they aren't at the same speed.



Dave

 

[DaveW]

You may very well cause your system to become unstable and start freezing
and giving errors.

 

[ck26]

This isn't an answer to your question - just another question / slant on the
same topic.

How does it work from the other way around: If you have a FSB of 100 and you
have 1 chip running at 100 then you add 2 133 chips? Does the machine (which
can only run at a FSB of 100) then drop all speeds (FSB and all memory
modules) to 100 automatically or does it depend on the BIOS and motherboard
settings?

 

[kony]

This isn't an answer to your question - just another question / slant on the
same topic.

How does it work from the other way around: If you have a FSB of 100 and you
have 1 chip running at 100 then you add 2 133 chips? Does the machine (which
can only run at a FSB of 100) then drop all speeds (FSB and all memory
modules) to 100 automatically or does it depend on the BIOS and motherboard
settings?

Adding PC133 memory would change nothing, the motherboard will attempt
to run it at same speed it ran previously, in this example 100Mhz.
Remember that "PC133" is only a RATING of the maximum guaranteed speed
of a memory module, it actually has nothing to do with the speed the
motherboard uses. The motherboards settings always "override" the
information stored in the memory SPD EPROM, including the MHz
frequency. Only the specific timings would override the motherboard's
settings, and only then if the motherboard is specifically instructed
to do so with a bios setting (whether that setting be user-changable
or hidden by manufacturer or system OEM).

There are a few rare exceptions when it comes to the number of memory
modules, some boards when detecting more than 2 (or more) will drop
down the memory bus speed, but this has nothing to do with the type of
memory installed.


Dave

 

[ck26]

Clear and concise as always, thanks Dave.

 

[JT]

This isn't an answer to your question - just another question / slant on the
same topic.

How does it work from the other way around: If you have a FSB of 100 and you
have 1 chip running at 100 then you add 2 133 chips? Does the machine (which
can only run at a FSB of 100) then drop all speeds (FSB and all memory
modules) to 100 automatically or does it depend on the BIOS and motherboard
settings?

All ram runs at the same speed

JT