Is there any difference in assigning variable to itself after some actions on it or to another variable?

Hi, Not long ago I had a debates about assignment variables to itself after some action on them. Assign variable to itself [AI]: echo memory_get_usage() . "\n"; // 645680 $repeatedString = str_repeat('Hello,', 10000); echo memory_get_usage() . "\n"; // 705944, AI_delta1 = 60264 $repeatedString = explode(',', $repeatedString); echo memory_get_usage() . "\n"; // 3337888, AI_delta2 = 2631944 echo memory_get_peak_usage() . "\n"; // AI_peak = 3401024 Assign variable to another variable [AAV]: echo memory_get_usage() . "\n"; // 645752 $repeatedString = str_repeat('Hello,', 10000); echo memory_get_usage() . "\n"; // 706024, AAV_delta1 = 60272 $explodedString = explode(',', $repeatedString); echo memory_get_usage() . "\n"; // 3398256, AAV_delta2 = 2692232 echo memory_get_peak_usage() . "\n"; // AAV_peak = 3400984 I created tests of memory usage in both cases and subtract values: AAV_delta1 - AI_delta = 8 AAV_delta2 - AI_delta2 = 60288 AAV_peak - AI_peak = -40 According to this results it doesn't matter which approach to use, memory usage - same. It's only a question should I use variable $repeatedString at my code below or not. Am I right at my conclusions or my tests are not correct? Why it happens this way? Also a question: AAV_delta1 - AI_delta = 8, I expect it should be equal 0. Why it's equals 8? Note: Memory usage can vary on your system. PHP Version: 5.3.5-1ubuntu7.11.