Chapter
3
Host Operating Systems
The major host operating systems (OS), such as Microsoft Windows, Apple Mac OS and
Linux, recognize a wide range of USB devices belonging to standard classes defined by the
USB Implementers Forum. Upon connection of the USB device, any host operating systems
perform the following general steps:
1
Enumerating the USB device to learn about its characteristics.
2
Loading a proper driver according to its characteristics’ analysis in order to manage the
device.
3
Communicating with the device.
Step 2, where a driver is loaded to handle the device is performed differently by each major
host operating system. Usually, a native driver provided by the operating system manages a
device complying to a standard class (for instance, Audio, HID, MSC, Video, etc.) In this
case, the native driver loading is transparent to you. In general, the OS won’t ask you for
specific actions during the driver loading process. On the other hand, a vendor-specific
device requires a vendor-specific driver provided by the device manufacturer. Vendor-
specific devices don’t fit into any standard class or don’t use the standard protocols for an
existing standard class. In this situation, the OS may explicitly ask your intervention during
the driver loading process.
During step 3, your application may have to find the USB device attached to the OS before
communication with it. Each major OS uses a different method to allow you to find a
specific device.
This chapter gives you the necessary information in case your intervention is required
during the USB device driver loading and in case your application needs to find a device
attached to the computer. For the moment, this chapter describes this process only for the
Windows operating system.
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