Control Program Facility (CPF) is the operating system of the IBM System/38. CPF represented a separate line of development at IBM Rochester and was unrelated to the earlier and more widely used System Support Program operating system. CPF evolved into the OS/400 operating system, originally known as XPF (Extended CPF).
On most computers before System/38 and on most modern computers, data was stored on the hard disk in separate logical files. When data was added to a file, it was written to the designated sector or, if the sector was full, to a new sector elsewhere. The System/38 adopted the single-level store architecture, with main memory and disk storage organized as a single unit, from the abandoned IBM Future Systems (FS) project. Each record was stored separately and could be stored anywhere in the system. There was no physically contiguous file on disk, and the operating system managed the storage and retrieval of all data items.