How much memory a PHP array can occupy

Recently read a large file in PHP to put the relevant data into the array, after processing and output, the reading process found to occupy a large amount of memory, so very curious about this problem.

Write a simple code.

<?PHP$m 1=memory_get_usage ();$arr=Array();$m 2=memory_get_usage ();$arr 2=Array(    ' Testa ' = ' Hello world1 ', ' testb ' and ' Hello World2 ',    );$m 3=memory_get_usage ();Echo $m 1.Php_eol;Echo $m 2.Php_eol;Echo' Usage: '. ($m 2-$m 1),Php_eol;Echo $m 3.Php_eol;Echo' Usage: '. ($m 3-$m 2),Php_eol;

The results are as follows

92216
92656
usage:440
93432
usage:776

The unit of Memory_usage is B (Byte), that is, an empty array is 440B, the content is 776B later, or very memory.