The host controller, or adapter, is a hardware layer contained within the host computer: in this case, a Windows CE–based platform. The host controller converts data between the format used by the host computer and the format used on the bus. There are two standard host-controller designs, open host controller (OHC) and universal host controller (UHC). OEMs are responsible for providing driver software for the particular host controller hardware present on their Windows CE–based platforms. Microsoft supplies a sample host controller driver that an OEM can use as a basis for a host controller driver (HCD). For more information about USB host controllers, see Writing an HCD Module.