We use 32-bit Firebird 1.5 CS with 64-bit Windows. While Win64 limits
a memory for one 32-bit application to 2G it doesn't limit the overal
memory usage. In classic every connection is a differet process. So
all you need is to calcultate the maximum memory you can give to each
connection. So for example if you have 16G memory and 500 concurrent
connections you should allow for approximately 16-20M in
DefaultDbCachePages which is per-connetcion in classic. And the OS
caches data as well so you don't need really big FB cache. From our
experiments we've found that values as small as 4M don't affect
performance dramatically. And of cource you need multi-core and/or
multi-cpu system to get benefit from classic. In our case 2 double
core Athlons handle rather intensive 100-connection application very
well.
There are some problems though. If you don't monitor the memory
consumption and it reachs the physical limit the OS begins to swap
process to HDD and all the system just slows down to zero. And in
classic you cannot see who is connected. You just see many FB
processes wthout knowing user logins. Sometimes we use "task kill" at
nights because stopping the server doesn't stop already working
connections.

Maxim.