The Option 03 adds digital outputs to the instrument. In the case of the AWG400 series, each channel on the instrument has a 16 bit wide digital output of the data that is feeding that channel's D to A converter. On the AWG410 you have 16, on the AWG420 you have 32 and on AWG430 you get a total of 48 channels of digital stimulus. Each channel has an output pod that provides HI levels of 2.3 min into a 50 ohm load / 4.6 V min into a 1 M ohm load and LO levels of 0.1 V into a 50 ohm load / 0.2 V into a 1 M ohm load. The output connector from the pod to the Device Under Test is a 34 pin header, with 0.025" square pins on .100 inch centers, giving you 16 data lines and clock, with alternating ground pins. On the AWG510, there are 10 digital outputs that are actually using a separate memory devoted exclusively as a digital channel. This gives you a purely analog channel 1 and a totally independent digital channel. The AWG520 utilizes the channel 2 memory as the source for the option 03 output. On the AWG500 series, "SMB" connectors on the rear panel are the connectors that are used for the option 03. Tektronix sells cables that have a BNC connector on one end and an SMB on the other end to allow you to adapt to other instruments (such as an oscilloscope) if needed.