What restrictions on resources of a server and time of scripts performance are?
Time of a script execution on the server is not more than 30 seconds. A user cannot use more than 3-10%(according to ordered hosting-plan) of server's resources, cannot use more than 64 MB of operating memory of the server, not more than 20 processess from one user at the same time. This restrictions apply only to the shared hosting. VPS and dedicated servers have no such restrictions – you can use all of a servers resources. On VPS we only control the resources of the main physical server.