 In the early 1960s the B5500 Master Control Program (MCP) operating system included virtual printers, called "Printer Backups" in the form of "Printer Backup Tapes" (PBT) and "Printer Backup Disks" (PBD).IBM's VM/370 operating system allows users to spool a virtual printer (or punch) file to another user, who can read it as input.This provides a basic means of file transfer.