Server 2008 multicast allows installation on multiple clients through a single image file transmission. There are two modes to Sever 2008 multicast:
-- Auto-cast - This is an always-on multicast that begins as soon as a client requests an image download. If another client requests the same image during the first image transmission, the second client will capture the remaining data and then request the missing pieces until it has the complete image. Clients can join the transmission at any time and still get a complete image. For example, imagine the multicast has begun and a client joins half-way through so it gets blocks 50-100 but missed 1-49. At the end of the transmission the WDS server asks if any client needs anything else. The client would respond "blocks 1-49 please." Those blocks would then be multicasted over the network for that, and any other client that may need them.
-- Scheduled-cast - This multicast session starts at a particular date and time, or when a specified number of clients request the image.
The trivial FTP (TFTP) component previously used by WDS was depreciated in Server 2008 so WDS is the only user. TFTP was moved into the WDS component with only the WDS-needed functionality implemented. TFTP was also re-architected from an acknowledgement position. Instead of sending an acknowledgment after each packet is received, a window size is established and an acknowledgment sent only after the number of packets in the window is received.
Another change is support for 64-bit extensible firmware interface as a boot option—an alternative to the BIOS. There is some drop in functionality. Support for remote installation services-type images is gone in Server 2008; it only supports Windows Imaging Format images.