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I've got four DIMM slots in my motherboard (MSI MS-7236 Version 2.2, 945P Neo3).

As I understand it the board supports up to 4GB, I've been running it with 2x1GB.

I've tried adding 2x1GB more RAM today.

The old sticks seem to work in either the A or B channel and the new sticks also seem to work in either the A or the B channel, but when I add any more than 2 sticks I get no graphics output at all on booting and I don't get any POST beeps where normally I get a success one.

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Are they all identical memory modules, same make and model? – Sandeep Bansal Aug 30 '11 at 11:27
No, not even the same make and a few years age gap. – rich Aug 30 '11 at 12:08
@Rich Are they at the same clock frequency? – BloodPhilia Aug 30 '11 at 12:47
Shouldn't think so. The old stuff seems to be labelled as DDR2 533 while the new sticks seem to be 1066. – rich Aug 30 '11 at 14:52
up vote 5 down vote accepted

If both sticks of memory work in both sets of slots, just not in both at the same time, the only thing I can suggest is:

  1. The two sets of memory modules are not compatible with each other / different speeds or timings.

  2. There is some sort of motherboard damage somewhere.

Sorry I can't really be more positive here.

All I can suggest is that if you can, buy two more of the same memory sticks again, and see if you can use all 4 the same.

It is never a good idea to mix and match, and, throughout the years, memory can change quite a bit and be incompatible with each other (Read this for a bit more info).

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If you can get a stable config that is validated by testing software. It is perfectly OK to mix different types of memory. I did this many times with great results. Furthermore, if the memory controller is damaged, you should have problems also with 2 sticks of ram.. – Ioan Paul Pirau Aug 30 '11 at 12:00
Thanks, at least I know that it's not unreasonable that sticks might be incompatible with each other even if they both work individually. Positive enough for me! – rich Aug 30 '11 at 12:12
@Ioan Paul Pirau, I still maintain what I said. Whilst it may be ok to do so (never said it wasn't), This is a dual channel machine and by having all sticks the same, it can significantly improve performance. By using different memory modules, it "may" work, but, it is very unlikely that dual channel will. – William Hilsum Aug 30 '11 at 13:01

Most probably, since you can use the old pair and the new pair, the two pairs are not compatible. You can validate this by trying to mix the two pairs.. use one stick from the first pair and one from the second, if it doesn't work just for the hang of it try with the other 2 sticks and if this also doesn't work then the memories are absolutely incompatible.
Note also that in most cases you can also put in 3 sticks of ram, it's not absolutely necesary to use pairs (unless your board can work with memories in dual channel) and you want to use that. Other than that if you find that there is any configuration when 3 sticks work.. you can also install 3 Gb. It will be much better in most cases then 2 Gb with dual channel.
If I were you I would try to combine all the sticks in any config to try to get a working configuration. Some ram controllers get the timings of the first stick from one bank and assume that the other stick(s) support the same timings. Therefore if you put the best ram in the first slot, the other ram sticks may fail since they do not support those timings. Don't worry about damaging your ram, if the config doesn't work.. it will not boot. Or it will boot with errors.. and that's why .. after you get a working configuration test it with a program like Prime95 that has specific tests for the memory.

Ioan Paul

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3GB would do me fine, I'm only just running out of RAM at 2GB. It looks as though even one stick of each type stops it booting. I'll just order two more sticks and cross my fingers I think! – rich Aug 30 '11 at 12:10
try again with 2 sticks but put them in reverse order, (preferably the older one in slot 0 and the newer one in slot 1) – Ioan Paul Pirau Aug 30 '11 at 12:12
I've tried that, I think I've tried just about every combination now! It doesn't seem to work at all with any combination of the two different types. – rich Aug 30 '11 at 12:14
Ok, then sorry but no luck. Your ram sticks are just incompatible. If you have another computer or a friend that has other 2x1 Gb sticks, you maybe can make a switch of ram.. and maybe his ram is compatible with one of the two pairs you have.. :) – Ioan Paul Pirau Aug 30 '11 at 12:17

From the OP (removed from the question):

I bought two more sticks of the same time and it now registers all four (or at least, 3200MB worth of them).

Thanks all.

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