Mac Pro (8 core) memory configuration issue

[celegans]

Hi,

I bought a refurbished Mac Pro (8 core) from the apple store and added 4 Gb (2x2Gb) to the 2 Gb tht came installed. I am having a peculiar problem in seeing all four of the memory modules. The only setup that shows all 6 Gb of the memory is to have the modules in the following format: a) 2Gb modules on Riser A, positions 1 and 3 plus 1 Gb mods on Riser B positions 1 and 3; b) 2 Gb and 1 Gb mods on Riser A positions 1 and 3, respectively, and the same on Riser B.

When I put them in the logically (and aesthetically better) intuitive configuration of paired mods in positions 1 and 2 of each Riser, I can only see the modules that are in position 1 of each riser.

Is this something expected in the new MacPros? Is there a disadvantage of keeping this configuration? I note that a memory installation video on line stated that the way memory is installed in the early 2008 Mac Pros has changed. Does this issue result from that change?

 

[edesignuk]

Is yours an "Early 2008" MP? I have 6GB in mine. 2x1GB stock in Riser A in 1 and 2, 2x2GB in Riser B in 1 and 2. Just as the manual advises. Works perfectly.

 

[celegans]

I think it is an "early 2008" model - how does one confirm this? I bought it refurbished from the apple site as an 8-core Mac Pro.

I think I tried the configuration that you mention and got a total of 2 Gb (i.e. only the Riser A group) recognized. I will have another look when I am at the computer.

 

[edesignuk]

I think it is an "early 2008" model - how does one confirm this? I bought it refurbished from the apple site as an 8-core Mac Pro.

I think I tried the configuration that you mention and got a total of 2 Gb (i.e. only the Riser A group) recognized. I will have another look when I am at the computer.

What processors does it have?

 

[CanadaRAM]

Welcome to MR

You'll find answers to this and many other commonly asked questions under the Guides tab at the top

Guides : Hardware: MR Guide to Buying RAM

Guides : Hardware: MR Guide to Understanding Intel Mac RAM

You have the RAM configured incorrectly.

Starting with your largest modules, install them in their pairs in this order

Riser A Slot 1, Riser A Slot 2 - 2 GB + 2 GB

B1, B2 - 1 GB + 1 GB

A3, A4

B3, B4

In general, it's recommended to have a Search in the forums and.or a look at the Guides before posting a new question.

 

[AppleNewton]

I think it is an "early 2008" model - how does one confirm this? I bought it refurbished from the apple site as an 8-core Mac Pro.

I think I tried the configuration that you mention and got a total of 2 Gb (i.e. only the Riser A group) recognized. I will have another look when I am at the computer.

which way is the TOP riser card facing?
ie; are the memory modules point up or are they point down?
and is there a bar/bracket between the memory riser?


the Early 2008 MP needs 800Mhz memory modules while the previous generation MP needs 667Mhz memory modules



RISER A
Slot 1 - 2Gb (upgraded)
Slot 2 2Gb (upgraded) make sure its 800Mhz if its the 2008 MP or 667mhz for the First Gen.
Slot 3 -
Slot 4 -

Riser B
Slot 1 - 1GB (original memory)
Slot 2 -1Gb (original memory)
Slot 3 -
Slot 4 -

 

[celegans]

Thanks everyone for the help. CanadaRAM, I first tried the configuration you describe, after finding it on various searches, As I recall, it didnt show the 6 Gb. Only then did I resort to the post.
AppleNewton, the top riser is facing down, this my conclusion that it must be an early 2008. I can't recall for sure (I am traveling at present), but it's possible that all the modules are 667 MHz, even the ones that came installed from apple! Despite the warnings about not using the older memory. I did read somewhere else on the 'net that 667s will work with with the new MPs but obviously you lose the speed advantage. I'll check all this when i get back.

celegans

 

[rhett7660]

I did a search and this is one of the threads that came up. So I thought I would ask it here.

I currently have a Mac Pro 2.8 that has 8 gigs of ram in it (8 x 1 gig sticks)(DDR2 FB-DIMM 800Mhz).

I want to do the following:Option 1

Riser A
1=2 (remove the one gig stick, replace with two gig stick)
2=2 (remove the one gig stick, replace with two gig stick)
3=1
4=1

Riser B
1=1
2=1
3=1
4=1
Total: 10 gigs

Or would have to do the following: Option 2

Riser A
1=2
2=2
3=1
4=1

Riser B
1=2
2=2
3=1
4=1
Total: 12 gigs

Due to price I am hoping I can do option one.... I am hoping I can. I am just a little confused since I have all my slots filled right now hence the reason for the question and I want to make sure I am reading and going to be doing this correctly.