Can a UDIMM be used in an RDIMM-supporting motherboard?

[173a]

Hello everyone,

So to clarify the question in the title, what I would specifically want to know is if the two are electrically compatible (DDR1 standard) and if inserting a UDIMM in a server mobo (said to support RDIMM) won't result in any burnt motherboard traces, but rather it may simply fail to POST, boot or display some error message? Please respond only if you have firm knowledge of or experience with the subject. I've found it surprisingly hard to get a definite answer to this topic on the internet and there's way too many guesses being expressed.

Thank you

[Tripredacus]

Post the board make and model

[173a]

It's the Tyan Thunder I7520D.

[jumper]

If they fit the socket without forcing (notches also match), they are pin and voltage compatible.

 

[173a]

6 hours ago, jumper said:

If they fit the socket without forcing (notches also match), they are pin and voltage compatible.

 

That's what I am kinda leaning towards too, but I've seen a story on electronics repair forum where a guy has managed to plug in either a registered or a registered-ecc ddr2 stick into a regular desktop board and that has resulted in burnt motherboard traces. This would be too expensive of a mistake to make, so I was hoping for some opinions with hands-on experience with the subject.

[Tripredacus]

Here's the manual https://www.tyan.com/manuals/m_s5360_100.pdf

It says 184-pin DDR 333/266 Registered ECC with single chip sizes of 256, 512 or 1024Mb. (their nomenclature)

Whether an unregistered will work, it is not going to be a 100% answer because all boards and RAM are different. You can go further by looking up the spec sheets of the RAM itself and compare them. But my experience tells me that there are going to be some boards where using UDIMM on RDIMM is going to either a) work fine, b) not work, c) not work fine or d) cause damage. So unless you can find any post online of someone who has tried the same exact RAM that you have in the same board rev and they say it works, then it will probably work. But real world isn't so handy to be able to find that info, so you are likely to have to try it yourself to see if it works or not.

I've also not experienced any situation where having an unsupported type of memory in a board has caused damage. Either with old Pentium systems or modern server boards. I suspect those instances of damage were likely caused by something other than mismatched memory, such as dirt or some other situation.

[173a]

So, partially answering my own question, I've tried it with a Tyan Tiger i7501 and the board beeps 7 times, code meaning "Non Reg/ECC DIMMs inserted". The board does POST with registered ECC DDR266, so it seems that at least with this particular model regular ram cannot be used.