Portable C Compiler

The Portable C Compiler (also known as pcc or sometimes pccm - portable C compiler machine) is an early compiler for the C programming language written by Stephen C. Johnson of Bell Labs in the mid-1970s, based in part on ideas proposed by Alan Snyder in 1973, and "distributed as the C compiler by Bell Labs... with the blessing of Dennis Ritchie."

One of the first compilers that could easily be adapted to output code for different computer architectures, the compiler had a long life span. It debuted in Seventh Edition Unix and shipped with BSD Unix until the release of 4.4BSD in 1994, when it was replaced by the GNU C Compiler. It was very influential in its day, so much so that at the beginning of the 1980s, the majority of C compilers were based on it. Anders Magnusson and Peter A Jonsson restarted development of pcc in 2007, rewriting it extensively to support the C99 standard.

The keys to the success of pcc were its portability and improved diagnostic capabilities. The compiler was designed so that only a few of its source files were machine-dependent. It was relatively robust to syntax errors and performed more thorough validity checks than its contemporaries.

The first C compiler, written by Dennis Ritchie, used a recursive descent parser, incorporated specific knowledge about the PDP-11, and relied on an optional machine-specific optimizer to improve the assembly language code it generated. In contrast, Johnson's pccm was based on a yacc-generated parser and used a more general target machine model. Both compilers produced target-specific assembly language code which they then assembled to produce linkable object modules.