Yahoo! has enhanced the APC opcode cache to support PHP-5.1. PHP-4.3.11 (optimized) 176.135 fetches/sec PHP-5.1 SWITCH 195.344 fetches/sec PHP-5.1 GOTO 198.707 fetches/sec PHP-5.1 CALL 199.342 fetches/sec PHP-4.3.11 (optimized) APC 209.342 fetches/sec PHP-5.1 CALL APC 252.968 fetches/sec The different VM models in PHP5.1 are very compiler sensitive. The following tests were run on a FreeBSD-4.3 system and compiled with gcc-2.95. On more modern compilers you should theoretically see better numbers from the GOTO VM, but the differences are usually not all that dramatic. ~/php51/Zend> php zend_vm_gen.php --with-vm-kind=GOTO zend_vm_opcodes.h generated succesfully. zend_vm_execute.h generated succesfully. cd .. ./buildconf ./configure ... make