  The technological prototype of the CALICE highly granular silicon-tungsten
electromagnetic calorimeter (SiW-ECAL) was tested in a beam at DESY in 2017.
The setup comprised seven layers of silicon sensors. Each layer comprised four
sensors, with each sensor containing an array of 256 $5.5\times5.5$ mm$^2$
silicon PIN diodes. The four sensors covered a total area of $18\times18$
cm$^2$, and comprised a total of 1024 channels. The readout was split into a
trigger line and a charge signal line. Key performance results for signal over
noise for the two output lines are presented, together with a study of the
uniformity of the detector response. Measurements of the response to electrons
for the tungsten loaded version of the detector are also presented.
