Backplane Hot Swap Modules are one the more popular “optional” items that are found in Windows Home Server machines. Norco SS-500 Backplane Hot Swap Module is a 5 bay module that fits in (3) 5-1/4” case bays. In order to squeeze 5 HD bays into (3) 5-1/4” case bays, Norco incorporates 2 distinct design features.  First, Norco mounts the bays vertically.  Second, the trays are designed to minimize width requirements by providing what appears to a cross between a full caddy system and a caddyless system.  There is no bottom to the caddy, only the front cover and side rails, as can be seen below.

More info: Cost $85.00 – Amazon | Norco