Apple only recommends what they have tested themselves on currently-shipping machines.
Since they didn't SELL denser DIMMs, they did not bother to test them before that Mac was discontinued.
There are four slots, the last two of which are shared. You can install 8GB DIMMs (pairing is not necessary) for very reasonable amounts of money, often, but not always the old DIMMs can be retained if desired. You can also install 16GB DIMMs under certain restricted conditions if you do not mind the expense. This Mac-centric Vendor has done their homework on the issue:
that was 2009 and 4x4GB was the max at the time.
I assumed you meant only supports an 8GB DIMM and 4x8GB is common. And affordable.
there are 8GB DIMMs at OWC that mix with other densities, nirmally they cannot.
4GB DIMMs were so expensive folks sacrificed GHz for DIMM slots going with dual cpu 8-core systems.
yes I realized after I opened the thread what you meant.
Apple should update such specs. 3x16GB is max with 4, 1 firmware.
Even the 2006 1, 1 (that I have) supported 16GB and confirmed to support 32GB as soon as 4GB DIMM existed.
A workstation, and there have been issues with more than 64 or 80GB but 96GB was also possible. And Mac OS Server 8x16GB. Dell, HP of course have Xeon with 196GB+.