I guess Pure Basic could run a server app, i'd think you are better off writing your server in the same language as the client though - this allows you to share rellevent source files and will reduce workload. Ultimately whether a language is 'fast' enough depends entirely on how fast the processor core the server applet runs on, how many players need to connect to the server applet, and how much processing your server side application needs to do per player.
If you are looking to scale up your MMO in the future you will likely have multiple server applets. One scenario might be
Global Chat Server (for handling long range /tell or /wispers)
<n> Global Voice Servers (for handling direct or group voice calls)
Login & Account Handling Server
<n> Servers Running a World Region
<n> Servers Running World Region Voice Chat
<n> SQL Servers (character and persistent state world storage & web site interaction)
Inventory Server
Probably a few more things besides, game design dependent.
Now all server applets can run on one machine, or as bandwidth and cpu requirements are reached you can break some off onto other machines. By using multiple applications, all communicating with each other and handing players over as needed, the language of choice becomes somewhat irrelevent as if a language is too slow, you just slap a faster CPU in or move some applets off to another machine when your player base allows you.
Also, as a point of reference to the multi-core/multi-threading debate. By using this model you can also see how a language doesnt need multi-threading on the server side, as the multiple applications will run on difference cores with the OS moving things between cores dependent upon load. External bandwidth from the I/O bus then becomes the limiting factor as to how much you can do with 1 machine.
If you are looking to scale up your MMO in the future you will likely have multiple server applets. One scenario might be
Global Chat Server (for handling long range /tell or /wispers)
<n> Global Voice Servers (for handling direct or group voice calls)
Login & Account Handling Server
<n> Servers Running a World Region
<n> Servers Running World Region Voice Chat
<n> SQL Servers (character and persistent state world storage & web site interaction)
Inventory Server
Probably a few more things besides, game design dependent.
Now all server applets can run on one machine, or as bandwidth and cpu requirements are reached you can break some off onto other machines. By using multiple applications, all communicating with each other and handing players over as needed, the language of choice becomes somewhat irrelevent as if a language is too slow, you just slap a faster CPU in or move some applets off to another machine when your player base allows you.
Also, as a point of reference to the multi-core/multi-threading debate. By using this model you can also see how a language doesnt need multi-threading on the server side, as the multiple applications will run on difference cores with the OS moving things between cores dependent upon load. External bandwidth from the I/O bus then becomes the limiting factor as to how much you can do with 1 machine.