What's the exact role of “significant characters” in C (variables)?

Question

What is the exact role of \"significant characters\" in C , especially in the field of variables? I have read the topic “(K&R) At Least the first 31 characters...”, but

Answer 1

In the old days of C, when the compilers and programs were run on machines with very limited memory (think kilobytes, not gigabytes) then to save memory the compilers only used up to eight (on the early compilers) characters of identifiers (names of variables, functions etc.). This is the role of "significant characters", it's the number of characters the compiler uses for names in the source.