The server requirements depend on the type of questions you are going to use. If you plan to use lots of Maple questions, then the preferable configuration would be a quad-core processor with 4GB of memory.

Otherwise, the default recommended configuration (dual-core with 2 GB of memory) could be sufficient. We would always recommend the superior server to ensure stability with any set of questions and to better future-proof your set-up.
 
If you expect to have more than 80 concurrent users then the following information will be useful:
  
1. Tomcat Web Server 
 
Tomcat should be configured so that it can accept and process all requests during the high load period. Tomcat HTTP Connector (defined in <tomcat>/conf/server.xml file) has a maxThreads parameter that sets the maximum number of concurrent requests Tomcat will handle. In general this parameter should be set high enough to accept at least one connection per user during pick period. In other words, if you expect maximum 300 users working concurrently with TA, you should set maxThreads to a value that is NOT LESS than 300. Otherwise users will experience either delays in processing or their requests will be rejected by Tomcat.
 
You can find details on Tomcat Connector setup in here:
 
Tomcat 5.5: http://tomcat.apache.org/tomcat-5.5-doc/config/http.html 
Tomcat 6.0: http://tomcat.apache.org/tomcat-6.0-doc/config/http.html
 
 
2. Postgres Database Server 
 
Postgres database server (similar to Tomcat) has a configuration parameter, which defines how many connections the server is allowed to accept from clients. The parameter name is max_connections and it is located in <postgres>/data/postgresql.conf file. Default value of the parameter is 100. This means that at any time there can be not more than 95-96 connection established with the database server by a client. 4-5 connections out of those 100 connections are used by the server for internal tasks.
 
max_connections value should exceed the expected maximum number of concurrent users in TA, because each TA user consumes one database connection. Do not forget about those 4 or 5 connections for Postgres internal use.
 
Postgres 8.2: 
 
http://www.postgresql.org/docs/8.2/static/runtime-config-connection.html 
http://www.postgresql.org/docs/8.2/static/kernel-resources.html
 
 
Postgres 8.3: 
 
http://www.postgresql.org/docs/8.3/static/runtime-config-connection.html
http://www.postgresql.org/docs/8.3/static/kernel-resources.html
 

Postgres 8.4: 
 
http://www.postgresql.org/docs/8.4/static/runtime-config-connection.html
http://www.postgresql.org/docs/8.4/static/kernel-resources.html
 
 
3. TA Database Connection Pool 
 
TA uses a database connection pool to serve users' requests to the database. This pool is configured in <tomcat>/webapps/mapleta/META-INF/context.xml. Again, there is a maxActive configuration parameter that should be adjusted if you expect to have a heavy load on TA. The default value for this parameter set by the TA installer is 100. This means that at any time TA will allow not more than 100 database connections opened by all users. During high load, it is highly probable that ALL concurrent users will ask for a database connection. If maxActive value is set lower than the number of concurrent users in the system, this may cause major delays in the system responses to users.
 
My recommendation would be to set maxActive value at least to the expected maximum number of concurrent TA users, but lower than Postgres (max_connections - 5) value (see previous section for details about max_connections parameter).
 

4. Maple Math Engine
 
Set "Max Servers" parameter in the "Maple Settings" section of "System Admin/System Settings" Maple TA screen to 10 if you expect up to 200 connections, and to 20 for up to 600 connections. You may have to adjust this later.