The Keyshark looks like a ps/2 connector and sits between the keyboard and your computer. It stores typing information in the non-volatile memory (which retains the information even when there is a loss of power.) This means that the Key shark device can be unplugged, and the information will not be lost.

USB keylogger is a tiny USB hardware module that plugs into keyboard. Just like the PS/2 version there is no software to install, just plug it in and it works.