USB human interface device class  In computing, the USB human interface device class (USB HID class) is a part of the USB specification for computer peripherals: it specifies a device class (a type of computer hardware) for human interface devices such as keyboards, mice, game controllers and alphanumeric display devices. The USB HID class is defined in a number of documents provided by the USB Implementers Forum's Device Working Group. The primary document used to describe the USB HID class is the Device Class Definition for HID 1.11. The USB HID class describes devices used with nearly every modern computer. Many predefined functions exist in the USB HID class. These functions allow hardware manufacturers to design a product to USB HID class specifications and expect it to work with any software that also meets these specifications. The same HID protocol is used unmodified in Bluetooth human interface devices. The Bluetooth profile specification only points readers to the USB HID documentation. In this sense those devices also belong to the USB HID class. Keyboards are a common kind of USB HID class device. The USB HID class keyboard is normally designed with an IN endpoint that communicates keystrokes to the computer and an OUT endpoint that communicates the status of the keyboard's LEDs from the computer to the keyboard. The PC 97 standard requires that a computer's BIOS must detect and work with USB HID class keyboards that are designed to be used during the boot process. Some keyboards implement the "USB Boot Keyboard" profile specified in the USB Device Class Definition for Human Interface Devices (HID) v1.11 and are explicitly configured to use the boot protocol. These are limited to 6-key rollover (6KRO) and will interrupt the CPU every time the keyboard is polled (even if there is no state change) unless the USB controller overrides this behavior. This profile is intended to allow the BIOS to handle a USB keyboard in the absence of a USB-aware operating system. The recommended profile for keyboards that are not in boot mode in this specification limits keyboards to 6KRO and causes them to respond to an interrupt with a status report at least every half second (again, even if there is no state change) in order to implement typematic (repeating the scancode when the key is pressed long enough) unless the USB controller is programmed to tell the keyboard not to do this. However, keyboards in non-boot mode are free to implement an alternative HID profile. The above-mentioned behavior is in contrast to the PS/2 interface, which supports "n"-key rollover (NKRO) for keyboards capable of supporting it.