Need to upgrade the IOS from 12.2 Mainline to get some new features, and it won't fit on the 16mb flash.
Cisco's website only shows support going up to a 20mb pcmcia card, but that is not quite enough.
AFAIK the max external memory card supported by 3640 router is 20MB only but some documentation says it supports 32 MB which could be documentation issue.
The internal flash of the 3640 can be upgraded to 32 using the following part number:
The above part number provides two 16 MB flash SIMMs that can be installed in the flash SIMM sockets on the motherboard to give you a total of 32 MB of DRAM.
If you want you can take second opinion from TAC or wait for some more experts to answer.
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