A computer program may also use cross-platform libraries, which provide an abstraction layer hiding the differences between various platforms, for things like sockets and GUI, ensuring the portability of the written source code.
From the start of computer automation in the early 1960s, if you wanted a report from data you had, or needed to print up invoices, payroll checks, purchase orders, and other paperwork businesses, schools and governments generated, you typed them up on a physical typewriter, possibly using pre-printed forms.
Starting in the late 1960s and early 1970s, efforts came into play to create standards and specifications of how machine-independent programs could be written using compilers from any vendor.
Standards-making organizations, like the International Standards Organization (ISO), and ANSI, among others, in cooperation with large users of computers and software (like governments, financial institutions and manufacturers), and computer manufacturers, to create standardized specifications to provide a description of how each specific language should be implemented.
Many of these are still in use, in some cases, because customers were able to take their source code to a different manufacturer's computer, where it was recompiled, often without change, because of the standardization of programming languages.