Hi
There are actually 3 hardware versions of the 837 router. One has 32MB on board, one has 48MB on board and the newest one has 64MB on board. Each version can only accept a 16MB DIMM so depending on which one you have the maximum memory is either 48MB, 64MB or 80MB.
I looked into this a while ago and found out I have the oldest one with 32MB on board and added a 16MB DIMM to take me to a maximum of 48MB.
HTH
Andy