Each tool's registration introduces a list of computation hosts where it is potentially available. This restriction might be necessary due to the existence of so called node-locked licenses which require that a tool is executed on a certain machine. Another reason for the restriction to a subset of the available hosts can be different computer architectures or operating systems. It is easily possible that a simulation tool is only available for some operating system. Furthermore, memory considerations might force a user to launch a simulation tool only on hosts where sufficient memory for a proper operation of the tool is available. It should be stressed that a registration is only necessary for tools which either are not available on every host, or for tools which have a limited number of available licenses.
Additional to the host at which a tool is available, the number of licenses available for that tool can be of importance. These licenses are usually a resource which is shared among concurrent users and, therefore, need to be managed carefully. Otherwise, situations occur where the automated occupation of tool licenses as it happens in SIESTA always grabs unused licenses before interactive users of simulation tools are able to do it. Therefore, the SIESTA tool registry offers a way to define how many licenses of a tool can be occupied by SIESTA.