Tandy 1000 MS-DOS Reference Manual page 59

Chapter 6 / Command Reference
backup c: store1 a: I i Id
copies to Drive A only those files from the STOREI (this
assumes STOREI is
a directory) directory on Drive C: that have
been updated (changed) since the last BACKUP operation. Cre-
ates a Backup.log file in the ROOT directory of Drive C:.
45