It seems like you’re asking about the “Fortran IV G1 compiler.” Based on historical context, this likely refers to one of IBM’s Fortran IV compilers developed for the System/360 series in the mid-1960s. IBM offered several Fortran IV compilers—named F, G, H, and later others—each distinguished by the amount of memory they required to operate and their optimization levels. The “G” compiler, in particular, was a widely used version, and “G1” might be a specific variant or a misremembered designation.

To clarify: Fortran IV (often associated with the 1966 standard, Fortran 66) was a significant evolution of the Fortran language, introducing features like logical IF statements and explicit type declarations. The IBM Fortran IV G compiler was designed for the System/360, requiring a modest amount of memory (typically around 64K bytes) compared to the more advanced H compiler. It was less optimized than H but more practical for smaller systems.

Unfortunately, no Fortran IV G1 compiler (or even G) is readily available today as a standalone tool, especially not for modern systems. These were proprietary IBM products tied to specific hardware like the System/360, and their original distributions are long obsolete. However, here’s how you might approach this:

1. Modern Compilers for Fortran IV Code: Most contemporary Fortran compilers (e.g., GNU Fortran gfortran, Intel Fortran ifort or ifx, or NAG Fortran) can compile Fortran IV code with minimal adjustments, as the language has maintained a high degree of backward compatibility. For instance:

• gfortran (part of GCC) supports Fortran 77 and later standards, which encompass Fortran IV features. You’d need to ensure fixed-format source (columns 7–72 for code, column 1 for comments with C or *) and possibly adjust for deprecated constructs like Hollerith constants.
• Intel Fortran compilers offer a -f66 flag to enforce Fortran 66 semantics, which aligns closely with Fortran IV.

1. Emulation: If you specifically need the IBM Fortran IV G compiler’s behavior (e.g., for historical accuracy), you’d need an emulator for the System/360, such as Hercules, paired with an original IBM OS like OS/360. The compiler itself would require vintage software archives, which are rare and often inaccessible outside of specialized collections or museums.
2. Practical Steps: If you have Fortran IV code you want to run:

• Rename the file with a .f extension (e.g., program.f).
• Try compiling with gfortran -ffixed-form program.f -o program. The -ffixed-form flag ensures it respects the old card-based layout.
• Fix any errors (e.g., outdated I/O statements like WRITE (6,10) referencing unit 6 for output might need adjustment depending on the system).

If “G1” refers to something more specific (e.g., a typo or a different system), could you clarify? For example, was this code intended for a non-IBM platform, or do you have a particular source file in mind? Without additional context, I’m assuming you’re seeking general information or a way to use such a compiler today.

Given it’s March 4, 2025, no original Fortran IV G1 compiler is in active use, but modern tools can bridge the gap. Let me know if you need help with a specific code example!