For the past few weeks we have been covering an issue where having more than 1GB of RAM in a Mac or PowerBook with an AirPort Extreme card could result in wireless network slowdowns and disconnects (see reports 1, 2 and 3), especially during periods of heavy network transfers. The only reliable solution that has appeared so far is removing RAM to reduce the total installed RAM.
It now appears that there is a specific reason this bug only affects those computers with more than 1GB of RAM and AirPort Extreme cards.
A posting on the PowerList PowerBook mailing list from a reputable source states:
"Only 30 of the 32 address lines were connected. That's 1 GB. If the AirPort Extreme tries to access (DMA) higher addresses, it fails and shuts down and you get no notice and no way to remedy it other than switching to ethernet or restarting.
"I've been on ethernet for 8 months now."
This appears to be internal knowledge at Apple, though no word on a AirPort Extreme firmware upgrade or other fix has emerged.