AJAX in PHP upload/download file

Please show me AXAJ in PHP to upload/download a file ..

Upload from a local path preserving the date modified.
Download to local path such as:
C:\_PHP_data\

This should be called over URL
This should have no interface

index.php?UPLOAD=HOSTPATH&LOCALPATH
index.php?DOWNLOAD=HOSTPATH&LOCALPATH

HOSTPATH = /_PHP_data/
LOCALPATH = C:\_PHP_data\TestFile1.sfo