Mac Pro RAM changing sizes within System Profiler

I've never heard of this either, but I did notice something interesting: you actually have memory from 2 different manufacturers installed in your system. One set of 4 has an ID of 0x8551 and the other 4 have an ID of 0x80AD. That doesn't add up if you bought them all at once from the same place.

Does anyone else have access to your tower who could have swapped memory? (I don't know if you're home or office based, but I used to manage a graphics team and when upgrading one system I would often replace memory modules right on down the line on all our towers...)

When Mac Pro (Tower) memories report themselves at half the size you know, they have FAILED. There is no need to run exhaustive memory tests. You have your evidence.

If they still have the 18004Memory sticker on them, return them for replacement under the Lifetime warranty.

it now reads as two of the eight cards are 2GB instead of the expected 4GB, so now my total RAM reads as 28GB instead of the expected 32GB. Any ideas? I've heard about people swapping out cards into different slots when the RAM wasn't being recognized at all, but this is different. I've not seen any mention in the forums regarding changing numbers (or at least I wasn't putting in the proper search parameters to find those posts). Any help or explanation would be much appreciated.

RAM reporting half or less than it should with FBDIMMs has become somewhat common.

Call it what you want, they are defective and can cause further trouble (writing bad data for one) so you need to pull them if you know which and get them RMA'd.

FBDIMMs run hot and using SmcFanControl 2.2.x is a good way to improve air flow and cooling properties to help insure components work properly (RAM, graphic cards) - and anytime you know you will be stressing resources just use higher fan profiles instead of the default or what you need for lite use. 850 rpm helps for lite use and can't hear the difference, 1000-1200 you begin to hear fans and get much better cooling. Above that to insure even under heavy work loads.

It is much easier to keep or prevent a system from getting too hot and keep it in cooler range than to wait for fans to kick in and then try to expel heat. Heat also remains and can build up during sleep, so running the fans @ 1500 rpm before shutting down or putting to sleep is a good idea.

Bad RAM is bad RAM though. I see this more often and common with 1-2 yr old FBDIMMs from a very popular vendor, but not from Kingston and Crucial. Vendors or resellers can have RAM from different sources and batches of course. They should also be warranted 100%.

my macpro actually did the exact same thing

currently it has 16mb of matched ram in 8 2mb sticks.

when i switched to windows vista through bootcamp all was fine, but when i switched back to osx from windows vista i only had 14mb, 2 of the sticks were reporting as 1mb each.

i rebooted and all was fine.

i tried the exact same thing and the same happened.

strange behaviour. ive not had to use windows for a few months now and my mac has been showing the full 16mb ever since.

I dumped Vista when Windows 7 Beta/RC but I never, ever, got difference in reporting of RAM.

Windows editions vary in how much RAM is supported but up to 16GB (not MB) seems Windows 7 Pro is only needed for more than that (or Business edition of Vista). And I needed Business or Ultimate for dual processor sockets.

Still sounds defective.