You can sign into any host since your home directory and data are equally available on each host. In general, anything you can do with one host, you can do with any of the four. So ideally you should pick one that is lightly used. The hosts have different processor speeds and different amounts of main memory, affecting their capacity. The hosts may run different versions of the operating system, affecting both the results from programs that run on the systems and also the capacity of the host.
Some software is only available on some of the hosts.
Forbin is used as a test bed when upgrading to different versions of the operating system. It is currently running Solaris 2.5.1, the same version of the operating system as the other hosts . Hydra Similar to Forbin except users are allowed to run CPU-intensive jobs on this host. This is principally used for jobs requiring more than 15 minutes of CPU time. All other hosts allow no processes to use more than 15 minutes of CPU time.