# 400 Mhz RAM in 266 MHz mobo-is it possible?



## imagineer_aman (Aug 22, 2005)

Hi team!
I have a doubt regarding the installation of a new Ram module in my
Mercury mainboard P4M266a.
This motherboard supports a maximum of 266Mhz Ram Speed.
Currently, I have a 256 MB 266Mhz DDR Ram module installed.
I want to discard this RAM module and install a 512MB RAM module.
Unfortunately, DDR RAM of 512 MB are available at 400Mhz speed only,
in my city. I'd like to know whether I can fit-in the 400Mhz Ram
module in my mainboard without causing any conflicts.
Please explain in detail( a little bit of theory always helps).
Thanks for clarifying,
Aman. 

My Pc specs are.. 
Celeron 2.4Ghz,256 MB DDR PC2100, Mercury Mainboard P4M266a, Windows Xp Home SP1,10 GB Samsung SV1022D.


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## AlienTech (Aug 22, 2005)

Yes you can install DDR400 but the mother board is rather pathetic. I would well get rid of the motherboard and use the 256MB instead of keeping the motherboard and getting 512MB.


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## pimpom (Aug 22, 2005)

Yes, you can use DDR400 memory on your mobo. Since you asked for a bit of technical explanation - The basic clock frequency of DDR400 is 200MHz and that of DDR266 is 133MHz. But DDR (Double-Data Rate) memory processes data twice in one clock cycle, so that they effectively work at twice the clock frequency, hence the name *Double*-Data Rate.

The speed at which memory runs is determined by the motherboard setting and not by the memory itself. The speed rating of a RAM module is the maximum at which it *can* work reliably, not the speed at which it _must_ run. It will work at a lower clock speed. It will run cooler and probably more reliably. DDR400 running at 266 may even be slightly more efficient than DDR266 running at the same clock.


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## imagineer_aman (Aug 22, 2005)

Thanks a lot for the quick replies AlienTech and pimpom. spl thanks to pimpom for technical clarification.
@alientech- ya i too want to get rid of the mobo but rite now my money bag is not heavy


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## AlienTech (Aug 23, 2005)

I have the same mother board and it is slower than my P3 866... In fact for a lot of things I can run my P3 500 faster and prefer it.  I am not used to crap mother boards and this one is in name a P4 motherboard.. But a really bad cheaply made one. I saw the reviews of the Via P266 chip set which said its rather fast. HEH! But whats the use of being fast when there is bottle necks almost every place on it.


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## imagineer_aman (Aug 24, 2005)

Hi AlienTech. Thanks for the feedback. Umm Right now, i aint in a position to buy a new mobo.So i guess i'll add 512 mb to the mobo in addn to 256mb- as u suggested-"dont throw away the ram".perhaps after 3 months when prices go down, i will buy a new mobo.Maybe 865GBF or 875.
But then, will i be able to install 256MB@266MHz AND 512MB@400Mhz without any conflicts??
Thanks for clarification.


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## AlienTech (Aug 24, 2005)

I think all the ram has to be the same speed or they ALL run at the slowest speed. I tried to use my old 266 ram with my new 400 ram and the system runs @ 266 and it is also not very stable. Seems to lock up after a day or so. Haven tspent any time tracking it down.


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## zombie (Aug 24, 2005)

Alien I advice you tune down 400 MHz to 266MHz because there wont be any difference in performance since as of now its trying to run at 266 MHz. But your system will be more stable if you clock it down to 266 MHz.

I had tried something similar with my SDRAM modules. 1 x 256MB @ 100 MHz & 1 x 256MB @ 133MHz. When I tried running both modules at 100MHz it worked fine. Speed was reduced but it was more stable.


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## AlienTech (Aug 25, 2005)

zombie said:
			
		

> Alien I advice you tune down 400 MHz to 266MHz because there wont be any difference in performance since as of now its trying to run at 266 MHz. But your system will be more stable if you clock it down to 266 MHz.
> 
> I had tried something similar with my SDRAM modules. 1 x 256MB @ 100 MHz & 1 x 256MB @ 133MHz. When I tried running both modules at 100MHz it worked fine. Speed was reduced but it was more stable.



I thought I mentioned that installing both 266 and 400 will run the system @ 266. But the problem seems to be the ram timings, the 400 runs @ 2-2-2-6 @ 133/266FSB while the 266 runs @ 2.5,3,3,6 @133/266FSB

Now I am not sure how they get that 6 in there with a rating of 2.5-3-3 since it should be 2.5+3+(2) thats a delay of 2 to get 7.5 since there is no 7.5 its 8. Maybe 7 max.... Maybe the motherboard is getting confused... The MSI RS480 does not even say it can accept 266 just 333/400 but when I installed it, it runs and shows @ 266 but crashes after a day to two. The 400 does not have the problem.


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## imagineer_aman (Aug 26, 2005)

Phew...that was really greek and latin to me AlienTech.cud u pls explain all those latency timing thing in an "easy to understand" way. Thanks. A little bit of theory always helps.


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## zombie (Aug 26, 2005)

*Oh I never thought about the timings.   *


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## AlienTech (Aug 27, 2005)

All ram chips have the 2-3-3-6 type stuff, they are the timings used between access to data as well as refresh intervals for ram etc etc etc... But these 4 are the most important and can affect system speed by upto 20%... The last number is the delay you give before each memory access since a too low value will get you garbage and a to high value will slow the system down too much. The value is calculated by adding the 2+3=5 then you just add a 2 cycle delay to this number getting you 7. As you can see the number 6 at the top of my note here instead of 7, which should cause problems....



There are a lot more than these 4 values.. A64Tweaker (look in google) lets you modify all these values.. Except my system just locks up.

Output from A64Tweaker... This is a WPCREDIT tweak for A64 systems only. It was written by CodeRed @ XS Forums. 

The A64 mem controller registers can be accessed using WPCREDIT using Bus #0, Device #24, Function #2. 

There are 4 main registers relevant to memory timings: 

0x88 DRAM Timing Low 
0x8C DRAM Timing High 
0x90 DRAM Configuration Low 
0x94 DRAM Configuration High 
The timings registers set all the DRAM timings params (as you'd expect), but there are many more than most BIOSes will show you. The best performance is obtained using: 

Column Address Strobe # (CAS) = 2.0 
Row Cycle Time (Trc) = 8 
Row Refresh Cycle Time (Trfc) = 12 
RAS# to CAS# delay (Trcd) = 2 
Row to Row delay (Trrd) = 2 
Min RAS Active Time (Tras) = 5 
Row Precharge Time (Trp) = 2 
Write Recovery Time (Twr) = 2 
Write to Read Delay (Twtr) = 1 
Read to Write Delay (Trtw) = 1 
I normally write this as 2-8-12-2-2-5-2-2-1-1 for convenience ...


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## imagineer_aman (Aug 29, 2005)

Thanks AlienTech.that was real good theory.i learnt something new thanks to u.I'll reply back when i get a ram module(preferrably 512 mb@266Mhz) and give the feedback.


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