3 DIMM slots in 2010 MP, 4th slot empty. Can I add another stick?

[malch]

This may be a stupid question, but because I have no idea why I put three 8GB sticks of RAM in my Mac Pro 2010, and left the 4th DIMM slot empty, I have to ask:
can I go ahead and add another 8GB stick of RAM in the 4th slot, or is there a reason to leave one slot empty?
I suspect I was short of cash, but for all I know I read somewhere to do it the way I did.
Can someone advise, please? Shall I fill the 4th slot with the same DDR3 1333 MHz RAM? (can a person buy one stick like this, or does it always have to come in pairs?).
thanks,
malch

[ClassObject]

Yes you can add moar ramz

[malch]

O.K., thanks...
Quick question:
If I get a new 8GB stick, will it 'match' an 8GB stick I got two years ago? (I remember reading somewhere that RAM has to be in matching pairs; I just don't know how particular you have to be about this)
regards,
malch

[Loa]

Hello,

Older 8GB ram sticks had to match. Try getting another identical RAM stick, from the same company. If you bought it from OWC, ask them before buying.

Loa

P.S. You probably used only 3 slots because someone told you that it would make your RAM faster. To make along story short: it was a lie! :-)

[Umbongo]

You should check your actual memory usage statistics before buying another DIMM. You may not benefit from 32GB over 24GB.

Get the part number of a module and post it here. 8GB DIMMs were only available as Registered ECC 2 years ago, but much is Unbuffered now. You can't mix them.

[DanielCoffey]

If you bought a matched set of 3x8Gb ECC a few years ago and now want to go to the full 32Gb, providing you match the RAM speed, timings and ECC but use a different manufacturer, you *should* be OK.

If the timings are different but everything else is the same, the worse case scenario is that you have to replace one 8Gb and buy a matched pair.

Remember ECC and non-ECC do not mix.

[malch]

Thank you all! Some really interesting information, that I never would have found on my own. Much appreciated.
Loa—you are absolutely right. I do remember hearing that 3 sticks would be better, for technical reasons that were beyond me... and I ended up getting 3 for that reason.
Umbongo and Daniel—I'm nervous about getting a wrong (unmatching) stick of 8GB, and ending up with four slots full but just three working. If I splurge (it's Christmas, after all) and get two new sticks of 16GB, will this work?
Or will it matter that these two new sticks might not 'match' my other two sticks of 8GB?
Umbongo—I'm a video editor, using Avid Media Composer. I've always assumed that more RAM is better, but maybe I should check into this, specifically for Avid.
Thanks,
malch

[DanielCoffey]

Why don't you post a pic of one of the sticks showing the sticker with the part number (make sure it is in focus). Someone might be able to suggest an exact stock number at an e-shop for the fourth stick. Just say which country you are in so they don't recommend a shop on the other side of the world.

Failing that, tell us what it says on Apple - About this Mac - More Info - Overview. You are looking for a line that says something like...

Memory 24 GB 1333 MHz DDR3 ECC

The key here is to see if you are using ECC or non-ECC memory. That is all you have to match if you want to take out the third stick and replace it with a new, warrantied matched pair.

On the assumption that you currently have a matched triple of 8Gb ECC sticks, you would be able to take one out and replace it with a matched pair of anyone else's 8Gb ECC sticks.

As long as all four sticks are EITHER ECC OR non-ECC you will be fine regardless of the brand. Just check the warranties and don't necessarily go for the cheapest option.

[jonnymo5]

Originally Posted by malch

Thank you all! Some really interesting information, that I never would have found on my own. Much appreciated.
Loa—you are absolutely right. I do remember hearing that 3 sticks would be better, for technical reasons that were beyond me... and I ended up getting 3 for that reason.
Umbongo and Daniel—I'm nervous about getting a wrong (unmatching) stick of 8GB, and ending up with four slots full but just three working. If I splurge (it's Christmas, after all) and get two new sticks of 16GB, will this work?
Or will it matter that these two new sticks might not 'match' my other two sticks of 8GB?
Umbongo—I'm a video editor, using Avid Media Composer. I've always assumed that more RAM is better, but maybe I should check into this, specifically for Avid.
Thanks,
malch

Technically 3 sticks will be faster to access than 4 but the difference is so small that you are only going to see it on benchmarks. This is because it uses a tri-channel I believe.

The reason for Umbongo's comment is that RAM is only useful if you are using it. If during your daily use of your computer you never utilize all your RAM then adding more wont make a difference. If you find yourself running out of memory and swapping to disk then you need more RAM.

That said, empty slots make me angry so I would fill it. You know, just to keep the dust out.

[All Taken]

Would your memory be quad rank? Might be worth considering - not sure of the performance hit in real world but it will down clock if it is quad rank.

[malch]

Originally Posted by DanielCoffey

The key here is to see if you are using ECC or non-ECC memory

Hi Daniel—just checked in System Information, and my memory is indeed EEC.
I also found my bill from OWC, which describes my order like this:

Quantity: 1 OWC1333D3X8M16K, $667.99 each
16GB (2x8GB) DDR3 ECC PC10600 1333MHz SDRAM PC3-10600 ECC for Mac Pro 'Nehalem' & 'Westmere' models. Lifetime advance replacement warranty

Jonny—I know what you mean about an empty slot being annoying. On the other hand, I will resist the urge to fill it if, indeed, I don't even use the RAM I've got in the course of a normal day's editing. I've never had a message come up saying I've run out of memory... does that mean that I don't need any more? I thought more RAM would make things even faster. Not that I'm bothered by any lag times when I'm editing. But, for example, when I want to check my audio tracks by adding waveforms, it takes my computer a few (long) seconds to do this. Again, not a big deal.

All Taken—not sure if my memory is quad or not...

Thanks everyone,
Malcolm

[minifridge1138]

You won't get any popups or warnings that you're out of memory.

To see if you're using swap:
1) Open 'Activity Monitor'
2) click on the 'System Memory' tab.
3) look at 'Swap used'

That's the amount of swap space you have used since the system booted.

If it says '0 MB', then you won't benefit from adding more ram.

[initialsBB]

Originally Posted by malch

Umbongo—I'm a video editor, using Avid Media Composer. I've always assumed that more RAM is better, but maybe I should check into this, specifically for Avid.
Thanks,
malch

More RAM is only useful for Avid MC 6 and up. It's useless for any version before that as it was 32 bit until v6.

[malch]

I'll check out Activity Monitor on Monday, fridge. Or should I do it Tuesday, after a full day of editing?
BB—I'm now using Avid Media Composer 6, so I'll be paying close attention to Activity Monitor.
Cheers everyone,
malch

[DanielCoffey]

Originally Posted by malch

I also found my bill from OWC, which describes my order like this:

Quantity: 1 OWC1333D3X8M16K, $667.99 each
16GB (2x8GB) DDR3 ECC PC10600 1333MHz SDRAM PC3-10600 ECC for Mac Pro 'Nehalem' & 'Westmere' models. Lifetime advance replacement warranty

So what have you actually got in the third slot then? That invoice was just for a pair of 8Gb. Do you actually have two slots free or what?

[malch]

Originally Posted by DanielCoffey

So what have you actually got in the third slot then?

I don't understand the invoice, then, because I know for a fact that I got the 24GB of RAM (three 8GB sticks) at the same time.
Here's a screen-grab from System Information:

hmmm... don't know how to insert a screen-grab (tried Insert Image, but that wants a URL link. I've got the screen-grab as a jpeg, on my desktop). Anyway, I'll quote it:
DIMM 1 8GB DDR3 EEC 1333 MHz OK
DIMM 2 8GB DDR3 EEC 1333 MHz OK
DIMM 3 8GB DDR3 EEC 1333 MHz OK
DIMM 4 Empty Empty Empty Empty

Thanks again for your help with this!
malch