# 第二章 PHP 底层原理

- [3.1 PHP底层的运行机制与原理](https://haxianhe.gitbook.io/php/di-er-zhang-php-di-ceng-yuan-li/php-di-ceng-de-yun-hang-ji-zhi-yu-yuan-li.md)
- [3.2 CGI、FastCGI和PHP-FPM关系解析](https://haxianhe.gitbook.io/php/di-er-zhang-php-di-ceng-yuan-li/cgifastcgi-he-phpfpm-guan-xi-jie-xi.md)
- [3.3 Session 原理解析](https://haxianhe.gitbook.io/php/di-er-zhang-php-di-ceng-yuan-li/session-yuan-li-jie-xi.md)
- [3.4 PHP 常见概念](https://haxianhe.gitbook.io/php/di-er-zhang-php-di-ceng-yuan-li/php-chang-jian-gai-nian.md)


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