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mac pro 08 ram problem dim 3 & 4 show nothing

dudeofblokes

dudeofblokes

macrumors regular
Original poster
Nov 3, 2007
238
15
carrickfergus, northern ireland, united kingdom
hey guys can someone please help i have a octo 2008 mac pro and bought Apple official ram to bring it up from 2gb to 6gb however the 3rd and 4th slots on each card dont reconnise ram listing them as empty, i thought maybe it was the ram and tried moving them around but got nothing in them each time, i also tried starting up with the original 2gb in bay 3 then bay for but the mac wouldnt start.

this is quite an annoying problem has anyone else discovered this? or know of a help. thank u in advance.
 
How many sticks of RAM do you have? Since you say 6GB, I'd imagine either four or six.

If you have four, put the first two Apple DIMMs in slots 1 and 2 on riser A and the other two in slots 1 and 2 on riser B. If you have six, do the same, but put the final two in slots 3 and 4 on riser A.
 
I think they are either not matched correctly or you have one bad Stick.

If you have one bad stick it will make 2 sticks not work because they have to be matched in pairs. I doubt you have 2 dead sticks.

Try using different combos of sticks and keep track of them so you can find the dead stick.

either that or you have one bad slot which would totally suck :(
 
Yeah do not use slots 3 and 4 on unless you have MORE than 4 sticks.

riser one use 1 and 2

riser two use slot 1 and 2


so if your using two 1 gig sticks and two 2 gig sticks.

do it like this

TOP RISER
slot 1 one gig stick
slot 2 two gig stick

BOTTOM RISER
slot 1 one gig stick
slot 2 two gig stick


if your using six one gig sticks it should be like this


TOP RISER
slot 1 one gig stick
slot 2 one gig stick
slot 3 one gig stick

BOTTOM RISER
slot 1 one gig stick
slot 2 one gig stick
slot 3 one gig stick
 
i have 6 sticks of 1gb and all sticks work perfect in the 1st two slots and have alternated them all so the fault doesnt lie there however the 3rd and forth slots show as empty and when i tested 3 and 4 with nothing in 1 or 2 nothing showed at all wouldnt start

the ram is perfect have tried mixing and matching and if in the 1st two slots they all work but 3 and 4 always report empty of to engineers i guess :(
 
Chaos123x said:
if your using six one gig sticks it should be like this


TOP RISER
slot 1 one gig stick
slot 2 one gig stick
slot 3 one gig stick

BOTTOM RISER
slot 1 one gig stick
slot 2 one gig stick
slot 3 one gig stick
Click to expand...

This is incorrect. If you are using six 1GB sticks, it should be as follows:

Top riser:

slot 1: 1GB
slot 2: 1GB
slot 3: 1GB
slot 4: 1GB

Bottome riser:

slot 1: 1GB
slot 2: 1GB
slot 3: empty
slot 4: empty
 
pastrychef said:
This is incorrect. If you are using six 1GB sticks, it should be as follows:

Top riser:

slot 1: 1GB
slot 2: 1GB
slot 3: 1GB
slot 4: 1GB

Bottome riser:

slot 1: 1GB
slot 2: 1GB
slot 3: empty
slot 4: empty
Click to expand...


nope they have to match cross risers not on the risers.

At least with the 2008 version.

EDIT: Nevermind I am wrong: Two pairs on the top memory card and one pair on the
bottom card.

It's confusing. I think mine might be setup wrong now.
 
Adding Memory Woes

I just purchased a Mac Pro with 2GB of memory and then ordered another 4GB from OWC (2 X 2GB PC6400 DDR2 ECC 800Mhz sticks).

As per the mac booklet I moved one of the original 1GB sticks up to the top riser and then inserted the 2 - 2GB OWC memory in the bottom riser.

I rebooted expecting the profiler to show 6GB.. nope only 4GB! I forget now, but system profiler showed sticks in only only riser.

After searching and finding this thread I moved the memory as per Chaos123x's suggestion...

Top riser

slot 1: 1GB stick original
slot 2: 2GB stick OWC

Botom riser

slot 1: 1GB stick original
slot 2: 2GB stick OWC

Now when I reboot system profiler says I have 1GB! Only Riser B slot one shows as having anything in it.

I tried swapping the 1GB sticks but see the same thing.

Any ideas?

Also which card (top or bottom) does system profiler label 'Riser A'?

Thanks
 
campadk said:
I just purchased a Mac Pro with 2GB of memory and then ordered another 4GB from OWC (2 X 2GB PC6400 DDR2 ECC 800Mhz sticks).

As per the mac booklet I moved one of the original 1GB sticks up to the top riser and then inserted the 2 - 2GB OWC memory in the bottom riser.

I rebooted expecting the profiler to show 6GB.. nope only 4GB! I forget now, but system profiler showed sticks in only only riser.

After searching and finding this thread I moved the memory as per Chaos123x's suggestion...

Top riser

slot 1: 1GB stick original
slot 2: 2GB stick OWC

Botom riser

slot 1: 1GB stick original
slot 2: 2GB stick OWC

Now when I reboot system profiler says I have 1GB! Only Riser B slot one shows as having anything in it.

I tried swapping the 1GB sticks but see the same thing.

Any ideas?

Also which card (top or bottom) does system profiler label 'Riser A'?

Thanks
Click to expand...
It should be:

Riser A slot 1: 2GB
Riser A slot 2: 2GB

Riser B slot 1: 1GB
Riser B slot 1: 1GB

Pairs should be matched in slots 1&2 or 3&4 and alternate between risers, so slots 1&2 get filled on both risers first. The only exception is that if using only two DIMMs optimum performance is gained by having a DIMM in slot 1 on each riser. Confusing, but it is covered in the manual.

The top riser is A.
 
campadk said:
I just purchased a Mac Pro with 2GB of memory and then ordered another 4GB from OWC (2 X 2GB PC6400 DDR2 ECC 800Mhz sticks).

As per the mac booklet I moved one of the original 1GB sticks up to the top riser and then inserted the 2 - 2GB OWC memory in the bottom riser.

I rebooted expecting the profiler to show 6GB.. nope only 4GB! I forget now, but system profiler showed sticks in only only riser.

After searching and finding this thread I moved the memory as per Chaos123x's suggestion...

Top riser

slot 1: 1GB stick original
slot 2: 2GB stick OWC

Botom riser

slot 1: 1GB stick original
slot 2: 2GB stick OWC

Now when I reboot system profiler says I have 1GB! Only Riser B slot one shows as having anything in it.

I tried swapping the 1GB sticks but see the same thing.

Any ideas?

Also which card (top or bottom) does system profiler label 'Riser A'?

Thanks
Click to expand...

Unfortunately both the configurations given in that post were wrong- your original configuration was actually correct for a 6Gb config with 2x1Gb and 2x2Gb, as can be seen on the OWC Memory Quicksheet for Early 2008 Mac Pros.

The same config can be reversed as well, so you might want to try that-- with the 2x2Gb in slots 1 & 2 of the upper card and the 2x1Gb in slots 1 & 2 of the lower card.

System Profiler lists the upper card as A by the way from what I remember. There is always a chance that one of the cards has not been fully inserted or is simply a defective card. Swapping the memory back and forth (keeping like sizes together as the memory sheet shows and checking the System Profiler each time) should help you quickly troubleshoot that.
 
Thanks sickmacdoc,

Forgot about images on OWC which are excellent.

I went back to top riser OWC and bottom riser original mac memory and profiler only showed 4GB on top riser.

However I then swapped and put them back as I originally had with the mac memory pairs on the top and the OWC pairs on the bottom and voila I have 6GB!

Really odd as I had tried reseating the sticks and the cards a few times but couldn't get it working... so who knows.

At least I now understand it all.

Thanks for your help sickmacdoc!
 
Actually here's the illustration taken from the official technical manual. It'll save you downloading the whole thing...



If you read, it suggest you pair the DIMM's in equal size or specs, which is kinda vague. I guess the rest is just experimenting, cause in my system it didn't like the smaller DIMMs in the upper riser, so had to move them about.
 
Please only follow official documents, with the Apple Manual and OCW's steps.

even the side panel of your MacPro has the proper procedure for MP memory installation.


Though its been stated on this thread already, it couldnt hurt to have it repeated and solidified:

Riser A (top)
Slot 1: 1GB (APPLE)
Slot 2: 1GB (APPLE)
Slot 3: 1GB (OWC)
Slot 4: 1GB (OWC)

Riser B (Bottom)
Slot 1: 1GB (OWC)
Slot 2: 1GB (OWC)
Slot 3:
Slot 4:


---

If it still is giving you issue, try this;
Place TWO 1GB sticks in Memory Slot 3&4 ONLY, leave the rest empty and try booting from there. if it boots and shows 2GB then that card is fine, try with the other card in the top slot as well.

another thing worth trying is:
Fill up the opposite card with all 4 slots of memory and put it in the top slot and just two sticks in the bottom and reverse it for each card to see if anything changes.

it could be a bad riser card or something or maybe an incorrect timed memory module, im not sure if OWC sends them individually or in pairs but even if it appears OK it might have some latency issues or something that just isnt sitting right and the rest of the memory is picking up the burden for that; basically cancells out the rest of the memory for safe system management.


hope that helps. good luck.
 
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