Peripheral Interchange Program (PIP) was a utility to transfer files on and between devices on Digital Equipment Corporation's computers. It was first implemented on the PDP-6 architecture by Harrison "Dit" Morse early in the 1960s. It was subsequently implemented for DEC's operating systems for PDP-10 and PDP-11 architectures.
PIP in CP/MEdit
Gary Kildall, who developed CP/M, based much of the design of its file structure and command processor on operating systems from Digital Equipment, such as RSTS/E for the PDP-11. Besides accessing files on a floppy disk, the PIP command in CP/M could also transfer data to and from the following "special files":
- CON: -- console (input and output)
- AUX: -- an auxiliary device. In CP/M 1 and 2, PIP used PUN: (paper tape punch) and RDR: (paper tape reader) instead of AUX:
- LST: -- list output device, usually the printer
- PRN: -- as LST:, but lines were numbered, tabs expanded and form feeds added every 60 lines
- NUL: -- null device, akin to /dev/null
- EOF: -- input device that produced end-of-file characters, ASCII 0x1A
- INP: -- custom input device, by default the same as EOF:
- OUT: -- custom output device, by default the same as NUL:
These were not true device files, however, because their handling was limited to PIP. The two custom devices INP: and OUT: were implemented as calls to fixed locations at the start of the PIP program; the intention was that the user, or the OEM, could patch these locations to add their own input or output devices. 246 bytes of free space were left in the program for this purpose.
In addition to the usual PIP destination=source syntax, PIP under CP/M still allowed the old PIP destination_source form. This behaviour was not documented, and CP/M generally did not have a standard for which characters could appear in file names; therefore other programs could and did create filenames containing underscore characters, which PIP could not handle.