What is the difference between RSH and SSH?

rsh and ssh are similar in that they can execute commands on remote systems. The main difference between the two (besides the actual TCP ports) is that rsh traffic is not encrypted and therefore a security risk; ssh traffic is encrypted.

The other main difference is that ssh is a secure replacement for telnet, whereas rsh can log into a remote system using the rlogin protocol, which is similar but not the same as telnet.