Why does count() make copies of arrays?

I was writing a shell script in PHP (4.4.2) that dealt with a rather large array. To figure out what I needed the new memory limit to be, I did a memory_get_usage() at the end of my script, and came up with about 5.5MB. I then set the memory limit to 8MB. When I tried to run it, the script ran out of memory on the line: $numwords = count($words); However, when I switched to simply incrementing $numwords every time I added an element to $words, the memory limit of 8MB was fine. So my question is, if PHP does copy-on-write, why does PHP make a copy of an array when you use count() on it, which should NOT be modifying the array? Regards, Adam Zey.