Here is a excellent Quora question: how many lines of code, if any, from Linux 1.0 are still in the modern Linux kernel, and what is it? And an evenly excellent answer:
According to git diff, 21228 of the 176250 lines from Linux 1.0 (1994-03-14) are still present in Linux 3.12 (2013-11-03):$ empty_tree="$(git mktree < /dev/null)" $ git diff --shortstat "$empty_tree" 1.0 561 files changed, 176250 insertions(+) $ git diff --shortstat -M -l99999 1.0 v3.12 44905 files changed, 17702349 insertions(+), 155022 deletions(-)
Over half of these lines are blank or consist entirely of punctuation; only 10419 of them have at least one letter or number.
We can go back even farther to the very first public release, Linux 0.01 (1991-09-17). Of the 10239 lines in Linux 0.01, 954 survive in Linux 3.12, of which just 242 have at least one letter or number. 123 of them were structs and constants in include/a.out.h (now include/uapi/linux/a.out.h), and 26 of them were the S_* macros in include/sys/stat.h (now include/uapi/linux/stat.h). The rest were scattered through 24 other files with at most 9 lines each.
It might appear that not much. But it is in fact impressive. How much code have you written that survived for over 20 years in a project that has changed so much – from a hobby experiment to a dominant operating system across servers, mobiles, and embedded devices?