This is a very useful way to remember it, but nowadays it’s better to drop the z (which immediately makes the mnemonic more forgettable, of course). tar can autodetect compression now, so tar -xf should work on anything from plain tar archives over tar.gz to more unusual compression algorithms like tar.xz or tar.bz2.

(the z is specifically for gzip)

And tar -czf compress ze file. I saw someone post these mnemonic devices a while back and now I actually remember tar commands. Amazing!