Implementations
The first implementation of numerical control was developed at the MIT Servomechanisms Laboratory in the early 1950s. In the decades since, many implementations have been developed by many (commercial and noncommercial) organizations. G-code has often been used in these implementations. The main standardized version used in the United States was settled by the Electronic Industries Alliance in the early 1960s. A final revision was approved in February 1980 as RS274D. In the world, the standard ISO 6983 is often used, although in varied states of Europe sometimes used other standards, example DIN 66025 or PN-73M-55256, PN-93/M-55251 in Poland.
Extensions and variations have been added independently by control manufacturers and machine tool manufacturers, and operators of a specific controller must be aware of differences of each manufacturer's product.
One standardized version of G-code, known as BCL, is used only on very few machines.
During the 1970s through 1990s, many CNC machine tool builders attempted to overcome compatibility difficulties by standardizing on machine tool controllers built by Fanuc. Siemens was another market dominator in CNC controls, especially in Europe. In the 2010s, controller differences and incompatibility are not as troublesome because machining operations are developed with CAD/CAM applications that can output the appropriate G-code for a specific machine tool.
Some CNC machines use "conversational" programming, which is a wizard-like programming mode that either hides G-code or completely bypasses the use of G-code. Some popular examples are Southwestern Industries' ProtoTRAK, Mazak's Mazatrol, Hurco's Ultimax, Haas' Intuitive Programming System (IPS), and Mori Seiki's CAPS conversational software.
G-code began as a limited type of language that lacked constructs such as loops, conditional operators, and programmer-declared variables with natural-word-including names (or the expressions in which to use them). It was thus unable to encode logic; it was essentially just a way to "connect the dots" where many of the dots' locations were figured out longhand by the programmer. The latest implementations of G-code include such constructs, creating a language somewhat closer to a high-level programming language. The more a programmer can tell the machine what end result is desired, and leave the intermediate calculations to the machine, the more (s)he uses the machine's computational power to full advantage.
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