Because your assumptions of how things work behind the scenes are not always correct. By profiling your code you can identify where the bottlenecks are quantitatively. PECL to the rescue! pear install apd downloading apd-0.4p1.tgz ... ...done: 39,605 bytes 16 source files, building running: phpize PHP Api Version : 20020918 Zend Module Api No : 20020429 Zend Extension Api No : 20021010 building in /var/tmp/pear-build-root/apd-0.4p1 running: /tmp/tmprFlAqf/apd-0.4p1/configure running: make apd.so copied to /tmp/tmprFlAqf/apd-0.4p1/apd.so install ok: apd 0.4p1 ]]> Then in your %php.ini% file: It isn't completely transparent. You need to tell the profiler when to start profiling. At the top of a script you want to profile, add this call: ]]> The use the command-line tool called %pprofp%: pprofp pprofp Sort options -a Sort by alphabetic names of subroutines. -l Sort by number of calls to subroutines -m Sort by memory used in a function call. -r Sort by real time spent in subroutines. -R Sort by real time spent in subroutines (inclusive of child calls). -s Sort by system time spent in subroutines. -S Sort by system time spent in subroutines (inclusive of child calls). -u Sort by user time spent in subroutines. -U Sort by user time spent in subroutines (inclusive of child calls). -v Sort by average amount of time spent in subroutines. -z Sort by user+system time spent in subroutines. (default) Display options -c Display Real time elapsed alongside call tree. -i Suppress reporting for php builtin functions -O Specifies maximum number of subroutines to display. (default 15) -t Display compressed call tree. -T Display uncompressed call tree. ]]> set_var2 0.0 0.00 0.00 0.00 0.00 0.00 0.00 1 0.0000 0.0000 0 test_class->set_var1 0.0 0.00 0.00 0.00 0.00 0.00 0.00 1 0.0000 0.0000 0 test_class->set_var3 0.0 0.00 0.00 0.00 0.00 0.00 0.00 1 0.0000 0.0000 0 test_class->set_var4 0.0 0.00 0.00 0.00 0.00 0.00 0.00 1 0.0000 0.0000 0 var_dump 0.0 0.00 0.00 0.00 0.00 0.00 0.00 1 0.0000 0.0000 0 test_class->disp 0.0 0.00 0.00 0.00 0.00 0.00 0.00 1 0.0000 0.0000 0 test_class->test_class 0.0 0.00 0.00 0.00 0.00 0.00 0.00 1 0.0000 0.0000 0 main 0.0 0.00 0.00 0.00 0.00 0.00 0.00 26 0.0000 0.0000 0 strtoupper 0.0 0.00 0.00 0.00 0.00 0.00 0.00 52 0.0000 0.0000 0 substr 0.0 0.00 0.00 0.00 0.00 0.00 0.00 1 0.0000 0.0000 0 implode 0.0 0.00 0.00 0.00 0.00 0.00 0.00 2 0.0000 0.0000 0 include 0.0 0.01 0.01 0.00 0.00 0.00 0.00 2 0.0000 0.0000 0 range 0.0 0.00 0.00 0.00 0.00 0.00 0.00 1 0.0000 0.0000 0 explode ]]> cd /tmp www:/tmp> ls -lat pprof.* -rw-r--r-- 1 nobody 4294967295 62771 Apr 17 07:36 pprof.02466.0 -rw-r--r-- 1 nobody 4294967295 269311 Apr 17 07:36 pprof.02465.0 -rw-r--r-- 1 nobody 4294967295 62779 Apr 17 07:34 pprof.02464.0 www:/tmp> pprof2calltree -f pprof.02465.0 Writing kcachegrind compatible output to cachegrind.out.pprof.02465.0 www:/tmp> kcachegrind cachegrind.out.pprof.02465.0 ]]>