The first PicLan implementation, Pick PC R83, had a very limited pool of PIBS and did not support phantom or background processes.
Some commands are simple, are executed to completion, and then are forgotten.
Other commands are more complex and may be broken up into many steps. While a command is waiting to be executed, it is placed on a run-queue. Other commands that wait for external events like network traffic may be placed on a sleep-queue. Each command type is designed to execute independently and with the possibility that other, possibly identical, commands may be requested concurrently. To illustrate the use of the pre-compiler, PicLan functions tend to make extensive use of Pick assembler user exits that subsequently call PicLan driver code which executes at the level of Pick monitor code.