PROCESS III - A Compiler-Assembler for No. 1 ESS

No. 1 ESS is a stored-program control telephone switching system. 1 ' 2 ' 3 The program consists of more than 100,000 instructions, each 44 bits in length, made up of 37 information bits and 7 check bits. To write such a program in binary (or octal) machine language is clearly impractical. To efficiently produce such large programs, modern techniques include the use of mnemonics or a symbolic language by the programmer. We say the programmer writes a source program in some kind of symbolic language, whereas the central control 2 executes an object program in its machine (binary) language. This article mainly describes the vehicle that translates No. 1 ESS source programs to No. 1 ESS object programs. Certain other items explain the progress of a No. 1 ESS program from inception as a source program to its final state as an object program. The vehicle developed for translating from No. 1 ESS source programs to No. 1 ESS object programs is itself a program; this program, named PROCESS III,* is executed on the I B M 7094 general-purpose computer. In keeping with the current usage for the words "compiler" and "assembler," PROCESS III is said to be a "compiler-assembler," since it performs both functions, as will be described. Consequently, in this article the words "compiler" and "assembler" are used interchangeably unless otherwise noted. * PROCESS is an acronym for PROgram to Compile ESS programs. 2457