DoubleDuty is a utility that uses the full 128K of a TRS-80 Model 4 to allow more than one program to be run at one time. Introduced by Radio Shack in 1984, DoubleDuty was written by Randy Cook, the author of Model I TRSDOS and VTOS.
DoubleDuty works by creating three sections, called partitions, out of the Model 4 memory. Partitions one and two each contain a complete Model 4 TRSDOS system. The third partition is reserved for running TRSDOS library commands.