The Atmel AVR ONE! main unit comes with a probe with the following capabilities:

An alternative probe can be purchased separately. This probe looks the same as the original probe but has the following capabilities:

The AVR ONE! firmware will automatically detect which probe is connected and refuse to connect to a 5.5V target through the MICTOR38 connector when using the original 3.3V probe. It is worth noting that the JTAG 10-pin connector has the same capabilities on both probes. It is only the MICTOR38 connector that differs.