The EWMA model is a special case of the GARCH (1,1) model with the additional assumption that the long-run volatility is zero.

A variance estimated from the GARCH (1,1) model is a weighted average of the prior day's estimated variance and the prior day's squared return.

The GARCH (1,1) model assigns a higher weight to the prior day's estimated variance than the EWMA model.

A variance estimated from the EWMA model is a weighted average of the prior day's estimated variance and the prior day's squared return.