PHP version history has been explained.
PHP Manual:
https://www.php.net/manual/en/
Contents cover:
01. June 1994 - PHP/FI
02. September 1994 - FI
03. October 1995 - Personal Home Page Construction Kit
04. April 1996 - PHP/FI
05. June 1996 - PHP/FI 2.0
06. 1997 - PHP/FI 2.0
07. June 1998 - PHP 3 - PHP: Hypertext Preprocessor
08. May 2000 - PHP 4
09. July 2004 - PHP 5
10. 2010 - PHP 6 (not published)
11. December 2015 - PHP 7
12. November 2020 - PHP 8
