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Is mixing ECC and non-ECC RDRAM a good idea...or even possible?

I have a 1.3 Gigahertz P4 Compaq Presario 7000T computer running Windows XP professional with 4 availible slots for Rambus ram chips.  The computer is used mainly for games, word processing, video editing, and music creation.

Currently there are two 64Mb Non-ECC chips in the motherboard, with 2 dummy chips.  The chips are made by Samsung.  Today I bought 2 Samsung 256Mb ECC chips off of Ebay.  I'm wondering if that was a mistake.  I have no experience whatsoever in upgrading memory, and my original plan was to take out the two dummy chips and place the 2 256Mb RDRAM chips in, giving me a total of 640Mb of RDRAM.  If I do that, will my computer run proberly, will it not even start up, or will it maybe damage something?  I read on a web site that someone said it is possible to mix the ECC and Non-ECC chips by doing something to the BIOS, causing the computer to assume all chips are Non-ECC.  Is that true?  If so, what?

If it turns out that it is not possible to mix ECC and Non-ECC RDRAM, will I at least be able to install the 2 256Mb ECC chips where my 2 64Mb Non-ECC chips were to give me 512mb of RDRAM?

Any help, tips, or ideas would be greatly appreciated.  Thanks a lot.
3 Solutions
You can mix the ECC RDRAM with non ECC RDRAM and it will be defaulted to non ECC if you mix the RAM. I don't think you have to set any changes to your BIOS as it will automatically be detected by your system. Beware, there have been a few reports of freeze-ups and instability if they are mixed together.
It's better to use the same type of RAM for your system and leave out the Non ECC RAM that you got as you can use the 2 ECC RAM on your system.
There is an option in the BIOS for DRAM ECC checking. Some options:

Older boards
Parity Checking Options
Parity Check
Memory Parity Check
Memory Parity/ECC Check

Newer boards
DRAM Integrity Mode (Default is "Normal" other option, "ECC")

These are found on the "Advanced Chipset" options and could have any of the above, depending on your BIOS Mfg.
Disabling these options would prevent the ECC. Your particluar board may have something different, but these options should be explained in the MoBo manual.


Just bung the RAM in and give it a go mate, see what happens. You wont damage the computer
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You can mix different types of RAM, but they would be working as the worst of the modules. So if you want to use ECC control instead of parity you have to remove non-ECC modules.
xxcspotxxAuthor Commented:
So does that mean that RAM that is non-ECC uses parity?  What's the difference between the two, and is one usually better than the other?
ECC is mainly used in Servers
Not the best idea to mix ECC and no-ECC RAM. Just a general rule of thumb is to never mix memory types so as to avoid flakey problems.  As stated above you may lose the benefit of the ECC RAM by installing it along with non-ECC RAM.  However you need to look at your motherboard manual to see if you system will even accept ECC RAM.  Have run into some boards where the ECC RAM will not be recognized at all.  

Again as above give it a try and see what happens.  Can't hurt.  If you find things a little flakey take out the non-ECC RAM (assuming the ECC RAM is woorking) that way you still more memory than before.

As to non-ECC always using parity that would be "no".  There is memory out there that uses a parity bit and some that doesn't.  Most ECC memory even uses a parity bit in conjunction with the ECC bits.  The ECC bits are set up through an error detection and correction algorythm then when the memory is read back the ECC bits are checked and if there is a single bit error detected the error will be corrected.  When more than one bit is found to be in error a double-bit error will occur which may or may cause the system to crash.  

Good Luck.
xxcspotxxAuthor Commented:
Thanks for all the info.  I don't really care if I'm able to use the ECC function of the new RAM.  The only reason I picked it up was because of the dirt-cheap price.  I think I'll just try putting in all 640Mb of RAM, if I get any problems, I'll just take out the original 128Mb.

I'm new to this place, and not really sure how this pints system works.  Everyone's answers have been helpful to me so far, is there a way to give every one some points?
Points can be split.  Go to


Post a zero point question there asking for points to be split amongst the following experts (name them).

Quote the question concerned


You may want to up the point slightly so it is divisible.


ECC (Error Correct Code) memory corrects memory errors it finds within itself.  Slower than other RAM types.
Parity memory checks itself and gives an error message if it finds itself faulty.  May lock up computer and stop it progressing any further in operation.  Originally in all IBM PC computers and clones.
Non-parity memory does no checking of itself.  Began to be installed in computers to cut costs.  Manufacturers claim it is reliable enought that errors do not occur.

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