Mixing SODIMM DDR333 and DDR400

Hi X-perts,

I am upgrading one slot of my notebook memory and it looks as the dealer has only DDR400, while my current set is DDR333.

Are there any problems of combining two slots of DDR333 and DDR400? Obliviously, the bus has 333 Mhz and both chips will run on 333. Should I just take DDR400 or it is better to look for DDR333?

Thanks you
andy7789Asked:
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Gary CaseConnect With a Mentor RetiredCommented:
It is possible that the i855PM chipset on that model may be sensitive to the higher speed modules.   A DDR400 module SHOULD work ... the memory makers claim full downward compatibility ... but laptop memory controllers are more sensitive than desktops => most of the problems I've seen with this have been on laptops (the most common are trying to use older PC133 modules in a PC100 laptop).

So should you "expect any troubles" ?? => No.   But it's certainly best to use a DDR333 module.   As long as your dealer will accept a return, there's no reason not to simply try the DDR400, however => it SHOULD work ... and it's a binary situation (it either works or it doesn't) => you don't have to worry about it working "sometimes" :-)
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Gary CaseRetiredCommented:
The DDR400 should work fine ... as you've noted, it will simply run at DDR333 speed.
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PCBONEZCommented:
That is if both modules are capable of operating at the same memory timings.
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http://www.amd.com/us-en/Processors/ComputingSolutions/0,,30_288_13265_13295%5E13335,00.html
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Gary CaseRetiredCommented:
With older SDRAM modules it was not uncommon for higher speed modules to not operate correctly at lower clocks; but with DDR modules I've never seen a case where the memory wouldn't operate at more relaxed parameters ... all of the major memory manufacturers "guarantee" downward compatibility [the "guarantee" isn't worth anything except the right to return it if it doesn't work].
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MarkCommented:
The only boards that I've ever had problems doing this were MSI boards that specified a DDR333 module. Most any other board would allow the DDR400 to clock down to the DDR333.
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MarkCommented:
FYI--> those MSI boards had Intel 845 chipsets.
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PCBONEZCommented:
I have an Asus 533 FSB board that specifies it won't work with DDR400 even if it's the only module. (Granite Bay chipset.)
I also have a FIC that doesn't say so in the docs but it won't take DDR400 even if it's the only module. (I845GV Chipset)
-
The manufacturers BIOS code comes into play here.
Since, we don't know what the board is, it is best to not make blanket statements.
Ya think?

.

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andy7789Author Commented:
Thank you all!

The processor is Pentium M 1600
Board: Compal 0860

Should I expect any troubles then?
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SgtSpikeCommented:
I'd give it a 98% of working with no problems whatsoever.
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uxlinConnect With a Mentor Commented:
I did similar things on my Dell and Compaq computers, not a bit a problem. Memories are kind of strange though - once in the old days I tried to use two different SDRAMs with the same speed but different brands, the system would boot up but would frequently crash. I'd suggest you go for it, get some sort of guarantee from the seller - if it causes problems, he should give you the option of returning it or exchanging it with some other product in the store.
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PCBONEZConnect With a Mentor Commented:
http://download.intel.com/design/chipsets/specupdt/25348802.pdf

The S-spec SL6TJ (A3 stepping) version of the i855PM only officially supports DDR266.
The S-spec SL752 (B1 stepping) version of the i855PM officially adds support for DDR333.

Both versions of the i855PM memory controller have a timing bug that makes them not fully JEDEC compliant.
(For the purpose here JEDEC specs essentially define how memory chips work.)

Given there are two possible chips and iffy JEDEC compliance with both of them weather DDR400 will work is anyone's guess.

Odds are it will work but I'm not giving it 98%. Maybe 85%, 90%? ??
It will depend on which memory controller you actually have, the memory modules and there ability to support DDR333 or DDR266 timings, and how tolerant the memory is JEDEC non-compliance.

If the dealer will happily take the memory back if it dosn't work then try it.
If the dealer won't take it back then find another dealer because you don't want a dealer with that attitude anyway.

.
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andy7789Author Commented:
I have installed Apacer PC3200 CL3 1Gb and it works fine.

The dealer had all Kingston and Corsair sold out... I am not sure whether to keep this one or try to get Corsair. I know that some tests show CL3 degrades in performance comparing with CL2.5 (though quite fractional).

I have never tried Apacer before.Any comments on this, please

Will Corsair CL 2.5 give me some noticeable defference in performance?
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Gary CaseRetiredCommented:
If the PC3200 is running at DDR333 speed it's most likely running at CL2.5 ==> the latency is a measure of delay time;  so CL3 at DDR400 represents fewer clock cycles of latency at slower clock cycles.

Run CPU-Z and click on the memory tab to see the actual frequency your memory is running at; and the SPD tab to see what the latency is for this module at the various speeds (you can select your modules individually on the SPD tab to see their parameters).  http://www.cpuid.com/cpuz.php

As long as your Apacer module has the same CAS latency as your current module at the speed your memory is running at there would not be any improvement with a faster module.   Apacer memory is fine ... and there's no reason to switch.
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andy7789Author Commented:
sorry, Corsair 1GB is CL3 as well, so I may have a choice:

1) Corsair VS1GSDS400    PC-3200          1GB         3-3-3-8
2) Apacer PC-3200 1GB CL3

Does Corsair worth hassles of replacing it with another dealer?
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andy7789Author Commented:
Thank you, i am running CPU-Z and there is the memory output:

DRAM frequency: 166.1 MHz (why? it should be 333)
FSB DRAM: 3.5
CL 2.5
tRCD 3
tRP 3
tRAS 7

The SPD tab shows the same column of  133 Mhz and 166 Mhz for both slots as CAS 2.5. Only the extra column 200MHz is presented for the second slot with CAS 3

Any comments?
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Gary CaseRetiredCommented:
166.1 MHz is correct => remember it's "double data rate" (DDR) ... so data is transferred on both clock edges => thus the data is double the clock (2 x 166MHz ~ 333MHz)

As I suspected, the CAS latency at that frequency is 2.5

... and there's no reason to swap the memory for any other brand (Corsair, etc.)

... as I said in the very first comment, "The DDR400 should work fine ..." ==> and it is :-)


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andy7789Author Commented:
garycase, thank you! Finally, i have decided to swap it to Corsair, because CPU-Z did not show me the manufacturer's info. Also, I have sarched the net and many people complain Apacer fails in two years (they provide a manufacturer's warranty for tree years only).  that A new corsair works ok, shows Corsair as a manufacturer and give exactly the same timing table as my original slot (Infineon)

One small thing that puzzles me: a new Corsair chip does not show its serial number in CPU-Z info window (Infineon does). Is it correct? You know, here in Australia we have hundreds of small dealers trading their parts from China... you never know that it is genuine and what is real.
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Gary CaseRetiredCommented:
I don't have any Corsair modules to check, but the serial # is simply a field in the SPD info -- if the manufacturer doesn't fill it in, it doesn't display.   I'd think Corsair would include it, but don't really know => and if the memory's working fine, I wouldn't worry about it.   On 3 systems I have handy, 5 modules report their serial #'s and 3 don't => but all work fine :-)

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uxlinCommented:
Hi andy7789 under general usage it's impossible to notice the difference in memory speeds, since the video card is more likely the bottleneck - if you don't have a good dedicated video card that is.

Glad the one you got is working. You mentioned that there are possibilities for fake stuff. So if the one you have isn't giving you any system crash, I'd suggest you to keep it and not exchange it for some nominally better but fake stuff - unless you have time to burn and like to experiment with new things.
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PCBONEZCommented:
>>>
... as I said in the very first comment, "The DDR400 should work fine ..." ==> and it is :-)
<<<

Yes, you played the odds and got lucky,,, with someone else's money..
Not something I'd be proud of...

.
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andy7789Author Commented:
Thank you guys - it is all ok, and I appreciate your help. One thing I am still trying to figure out is whether there are chances the chip is fake.

CPU-Z shows only manufacturer, part number, but not serial number and week/year. I understand that even if it is fake the quality could be the same as for Corsair, as they could assemble it from the same parts. The dealer is listed on the Corsair's dealer page; however, you never know if they trade partly fake and partly genuine. (All those dealers here are just 2-3 guys with one desk sitting in the industrial hangar full of computer boxes)

I am just wondering is there a way to distinguish between fake and real chips?
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Gary CaseRetiredCommented:
".. is there a way to distinguish between fake and real chips? " ==> This would be very difficult to do unless the labeling on the chips themselves is notably different.   The only other thing would be to check with Corsair r.e. the SPD info -->  if they always include serial # and week/year data then you'd know that the modules you have aren't legit.

... but the simple fact is that if the memory's working well I'd just leave well enough alone.   Even if it's "fake", the performance will be identical if it's running at the same speed and timing parameters.

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SgtSpikeConnect With a Mentor Commented:
The serisl number should be listed on the sticker on the ram stick itself though, so you may as well use that serial number to register for warranty through Corsair.  If the warranty registration goes through, I'd say it's a safe bet that the memory isn't fake.

You could also take the stick out and take a look at the numbers on the individual chips.  Google them, and see what you come up with.
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andy7789Author Commented:
SgtSpike, Corsair does not have options to register online. Anyway, I have contacted them to check if serial number in the chip data is mandatory.
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