Quick Ram Configuration Question 5.1

[RoastingPig]

so im running a 3.2 ghz 5.1 mac pro and im wondering will this ram configuration work its 4gb in slot 1, 2gb in slot 2, 2gb in slot 3 and 1gb in slot 4.

update, i tried it and the 1gb in the 4th slot did not post. is there something i should know about it..i heard something about having to be in pairs?

 

[flowrider]

The Intel CPUs are have three memory channels. Optimum performance is achieved when three equal sized sticks of RAM are used in slots 1, 2, and 3 leaving slot 4 empty. I assume from your post that you have a single CPU machine. Slot 4 is tied to slot 3 and if slot 3 is not populated the UDIMM in slot 4 will not be recognized.

Apples instructions appear below.

Lou

 

[RoastingPig]

So ram in slot 3/4 have to be identical? ...and 4-2-2-1gb would not work but something like 8-4-2-2 would because 3/4 have matching 2gb sticks?

 

[flowrider]

^^^^That's my understanding. Note, also, that for optimal performance, slot 4 should be left empty.

Lou

 

[DanielCoffey]

But if you have very little RAM like the case above, a bit more over four channels is better than a bit less in three.

 

[RoastingPig]

Is there a definite answer that says that 3/4 must be identical to work? If i moved 2x2gb into slot 3/4 it would post but if i put just a single 4gb in slot 4 it wouldn't post because there has to be a 4gb in slot 3 in order for the 4gb in four to work

 

[flowrider]

^^^^We're spending much time here on this. Try it to see what works and use the Memory Slot Utility to see what it says. I've attached more of Apple's instructions on 3 Channel RAM. Things I know.

1. The Intel CPUs use three channel memory.
2. Slots one and two are separate channels.
3. Slots three and four share one channel.
4. If slot four is populated and slot three is not populated, the Ram in slot four will not work.

My guess is, since Slot Three and Slot Four share a channel they should match for the RAM in slot 4 to work - I'm not sure of this, however.

Lou

 

[tamvly]

The Intel CPUs are have three memory channels. Optimum performance is achieved when three equal sized sticks of RAM are used in slots 1, 2, and 3 leaving slot 4 empty.

My understanding is that optimal is really only a couple of percentage points. So populating slot 4 is really not a big deal. Correct?

 

[flowrider]

^^^^Correct, it's there for those who choose to use it. IMHO, Apple chose to add the forth slot to the three channel CPU, to continue the tradition of earlier Macintoshes starting way back in January 1986. The first Macintosh with replaceable memory was the Macintosh Plus. It also had four memory slots populated with 4 256kb simms for a total of 1MB of RAM. You could upgrade it to 2.5MBs or all the way up to a whopping total of 4MBs.

If I had been apple, The Mac Pro would have only three slots for the three channels. Will it really degrade performance to use the forth. Not a big bunch, in fact some folks don't even notice it. Me, my slots 4 and 8 are MT.

Lou