in the 90's, Xmodem seemed to be a inferior protocol compared to Z-Modem and HS-Link.
replies(4):
They were successor protocols designed and implemented to fix perceived shortcomings in the original one.
1977: https://en.wikipedia.org/wiki/XMODEM
SModem supported simultaneous upload/download and chatting.
I sure miss those days. First modem was 2400 baud, so I was kind of a late comer.