From Halopedia, the Halo wiki
By default, the Halo 3 File Share can hold up to six custom content items; players who subscribed to Bungie Pro (at the cost of 750 Microsoft points per year) would have their File Shares expanded to hold twenty-four items. For a limited time, Bungie Pro was free for four months with the purchase of the Legendary Map Pack. File Share items were also displayed on Bungie.net. From Bungie.net, they could be organized into groups (called “File Sets”), tagged or downloaded to a computer.
On March 31, 2012, Bungie.net stopped updating File Shares. All record-keeping was transferred to Halo Waypoint. Reach File Share items were first displayed on the Waypoint website in June 2012. Halo 3 and ODST were not transferred, and as such are now only updated in-game. Halo Waypoint incorporates the same features previously found at Bungie.net, with the notable difference that the Halo: Reach File Share more than quadrupled in size from six items to 25.
Halo Waypoint also includes a feature known as the File Browser in which players can view and download files other players have uploaded to their Halo: Reach and Halo 4 file shares.
Halo 4 launched with an in-game File Share featuring 25 slots and all the same features as previous incarnations. It was not until February 2013 that the Halo 4 File Share was integrated into Halo Waypoint.