Today’s Unix/Posix-like operating systems, even including IBM’s z/OS mainframe version, as seen with 1980 eyes are identical; yet the 31,085 lines of configure for libtool still check if <sys/stat.h> and <stdlib.h> exist, even though the Unixen, which lacked them, had neither sufficient memory to execute libtool nor disks big enough for its 16-MB source code.