Mac Pro RAM install order

[Vedat]

I am curious to see if anyone out there can shed some light to this.
I have 2x2Gig and 4x1Gig chips I want to put in our Jan2008 (800Mhz) Mac Pro.
No matter how I put them it fails to see 2 of the 1Gig chips.
It used to have 4x1gigs without issues.

[Jeffrey Talbot]

There IS a special order in which they must be installed, and as I recall, it wasn't exactly intuitive..... Check with the documentation that came with the computer to see the order in which they must be installed.

I think they have to be in pairs... but pair order didn't seem obvious... at least to me.

[TimNielsen]

They have to be installed as matching pairs. There are 8 slots on the Mac Pro (2008) and think of them as 4 pair of slots. Aside from that, as long as the pieces match, it should work, assuming the ram is compatible, etc.

I had a similar problem, and it was definitely bad ram. Just wasn't showing up. And having one bad piece of ram will keep the 'bank' from showing up, so if you have two 1-Gig rams in there, and one is bad, that 2-gigs of ram will not show up.

The riser cards on the Mac Pro for memory actually have some LEDs on the motherboard next to them. They will light 'red' to report any errors. So check for that, with the computer on, look near the ram cards for a glowing red LED.

But my guess is either that you have a piece of bad ram, or perhaps a bad slot on the riser card, these are common enough too, bad slots.

But by changing out one chip at a time (among your 1 gigs) you might be able to find which one is bad. Start with the 2 gig chips installed (if you're missing two gigs, it has to be the 1 gigs since they work in pairs, if the 2 gigs were freaking out, you'd be missing 4 gigs of ram, if that makes sense).

Try two of them. You should have 6 gigs in the computer. If you only see four, you know something is up with either those two 1gig chips, or the slots that they are in. So next move that pair of them to two other slots. If the ram shows up, then it's the slots. If not, it's the chips.

[studiomusic]

You should have a diagram on the inside of the door you take off to get to the inner workings that shows you the order.

[Vedat]

So the winner combo is:

BAY1:
1GIG
1GIG
2GIG
2GIG

BAY2:
1GIG
1GIG


I should've just popped them in instinctively, and not watch that youtube video.
Thanks all.

[ctyelvis]

Yeah, I don't think mixing ram on the Mac Pros is a good thing. My buddy had 8 gb that came with his Mac Pro from Apple and bought an extra 16gb. But he then tried to use his stock 8gb of Apple ram with the new RAM. It appeared okay and worked fine, but holy crap, in the course of an hour the Mac was kicking out a LOT of heat!! So much, that it started to melt the Mac's power cable.
I'm not sure why that happened but everything was fine once he just installed the 4 new sticks of 4gb by themselves, in the order Apple recommended. I believe it was 2 sticks on each tray installed closest to the side that plugs into the Mac's mother board.

-Chris