The AIFF file format, used for audio, is by default uncompressed and lossless. However, it does have a lossy compression option. AIFF uses Pulse-code modulation (PCM), and therefore encodes time-varying pressure data.
The WAV file format is also by default uncompressed and therefore lossless, and like AIFF, also has a lossy compression option. Also similar to AIFF, WAV uses PCM to encode time-varying pressure data.
AU is uncompressed and lossless by default, but has a lossy compression option. Like the other two, AU encodes time-varying data with PCM.
Part III: not here yet.