http://php(as the current mainstream development language)-accelerator.co.uk/ can be downloaded and is a strong opponent of zend. It's free. I'm already using it. The effect is not bad.
Modify php(as the current mainstream development language).ini and add:
zend_extension = /usr/local/lib/php(as the current mainstream development language) _accelerator_1.3.3r2.so
php(as the current mainstream development language)a = on
php(as the current mainstream development language) a.tweaks = on
php(as the current mainstream development language)a.cache_dir = /tmp
php(as the current mainstream development language)a .file_perms = 400
php(as the current mainstream development language)a.cache_file_prune_period = 1h
php(as the current mainstream development language)a.cache_file_ttl = 1d
php(as the current mainstream development language)a.shm_size = 10
php(as the current mainstream development language)a.shm_key = 0xc0deb00
php(as the current mainstream development language)a.shm_perms = 666
php(as the current mainstream development language)a.shm_user = nobody
php(as the current mainstream development language)a.shm_group = nobody
php(as the current mainstream development language)a.shm_release_at_exit = on
php (as the current mainstream development language)a.shm_stats_check_period = 5m
php(as the current mainstream development language)a.shm_ttl = 12h
php(As the current mainstream development language)a.shm_max_processes = 512
php(As the current mainstream development language)a.shm_lock_threshold0 = 10
apache(The most popular WEB server platform on Unix platform)ctl graceful will work. See its documentation for specific parameters.