The choice of configuration is largely cost-based, because it depends on:

A small ETM is adequate for instruction trace. However, data tracing is less satisfactory with a small configuration, because the small FIFO and lack of support for the 21-pin interface reduces the data that can be traced without overflowing. The only implementations of the small configuration are in ETM7 and ETM9.

A medium-sized ETM gives reasonable data trace under most conditions. It is the configuration chosen by most users of ETM7.

Mediumplus is a medium-sized ETM configuration with a large FIFO. This configuration is only supported in ETM9 and is the ETM9 configuration chosen by most users.

The large ETM adds extensive triggering facilities and an enlarged FIFO. The large FIFO helps to smooth out short bursts of data trace.

Not all configurations are available for all implementations. Any future ETMv1 implementations are likely to be available only in the Mediumplus configuration.