what does Direct Attached Storage DAS mean in windows server 2008.
what does it do or can it be useful for a user using a server
Direct-attached storage as a computing term is not specific to Windows 2008.
Typically, DAS refers to the hard disks that are physically connected to your server (via SATA, SCSI or SAS).
It is usually considered opposite to 'NAS' which is network-attached storage (storage that the server can access over the network that is typically served by another server -- e.g. FTP, SMB/CIFS, NFS)