php download and upload stuck in some point

$download_rate = 200000; // here ob_clean(); ob_start(); header('Content-Description: File Transfer'); header('Content-Type: application/octet-stream'); header("Content-Disposition: attachment; filename=\"".basename($fileInfo['file_name'])."\";" ); header('Expires: 0'); header('Cache-Control: must-revalidate'); header('Pragma: private'); header("Content-Length: ".filesize('uploads/'.$fileInfo['file_name'])); ob_end_clean(); flush(); $file = fopen($local_file, "r"); while(!feof($file)) { // send the current file part to the browser print fread($file, round($download_rate * 1024)); // flush the content to the browser flush(); // sleep one second sleep(0); } fclose($file); i have some problem downloading files i always see the error [09-Jan-2016 12:41:48 UTC] PHP Fatal error: Out of memory (allocated 614989824) (tried to allocate 614404096 bytes) in C:\Inetpub\vhosts\[login to view URL]\httpdocs\[login to view URL] on line 87 [09-Jan-2016 12:45:52 UTC] PHP Fatal error: Out of memory (allocated 614989824) (tried to allocate 614404096 bytes) in C:\Inetpub\vhosts\[login to view URL]\httpdocs\[login to view URL] on line 87