Capabilities (Symbian Signed)/ProtServ Capability
The ProtServ (protected server) capability is required to register a protected server name (one beginning with the ! character). Processes without this capability have their thread priorities capped - they cannot run at higher priority than important system servers.
This capability can be used with developer certificates and Symbian Signed tested applications, and by using open signed online for testing.
Many system servers in Symbian OS are transient - that is, they shut down when not in use to save memory. A protected name prevents an untrusted process from spoofing or unintentionally clashing with a system server, while still allowing the client/server framework to be used by all. A thread running at very high priority can starve the system of CPU and cause the device to "lock up" because the window server has no chance to refresh the screen.
The kernel checks this priority when a process registers a server, or changes its thread priorities.
ProtServ is needed by any plugin to a system server.