Based on an offhand comment at https://www.extraputty.com/features/zmodem.html https://www.extraputty.com/features/zmodem.html, they were `sz` and `rz`. Wikipe

Based on an offhand comment at https://www.extraputty.com/features/zmodem.html https://www.extraputty.com/features/zmodem.html, they were `sz` and `rz`. Wikipedia (https://en.wikipedia.org/wiki/ZMODEM https://en.wikipedia.org/wiki/ZMODEM) says that this came out of the BBS days. Boy, that takes me back.