O-code machine

The O-code machine is a virtual machine that was developed by Martin Richards in the late 1960s to give machine independence to BCPL, the low-level forerunner to C and C++. The concept behind the O-Code machine was to create O-code output (O stands for Object) through the BCPL compiler. The O-code was then either interpreted or, more normally, compiled to machine specific code. This idea was used in later compilers. For instance p-Code for some Pascal compilers; the JVM code for Java compilers. O-code allowed Richards to separate general compilation issues from machine specific implementation issues when writing the BCPL compiler. Its use in the BCPL compiler made the compiler easy to port and as a result BCPL quickly became available for many machines.

For references see

"The Portability of the BCPL Compiler", Martin Richards, Software - Practice and Experience, Vol. 1, No. 2, pp.135-146, 1971

BCPL - the language and its compiler, M. Richards and C. Whitby-Strevens, Cambridge University Press, Cambridge, 1980