USB transfer modes
Univeral serial bus supports Control, Interrupt, Bulk and Isochronous transfer modes.USB transfer rates: Low Speed, Full Speed, Hi-speed.
USB supports three data rates: Low Speed (1.5 Mbit per second) that is mostly used for Human Input Devices (HID) such as keyboards, mice, joysticks and often the buttons on higher speed
devices such as printers or scanners; Full Speed (12 Mbit per second) which is widely supported by USB hubs, assumes that devices divide the USB bandwidth between them in a first-come first-serve
basis - it"s easy to run out of bandwidth with several devices; Hi-Speed (480 Mbit per second) was added in USB 2.0 specification. Not all USB 2.0 devices are Hi-Speed. A USB device must indicate
its speed by pulling either the D+ or D- line high to 3.3 volts. These pull up resistors at the device end will also be used by the host or hub to detect the presence of a device connected to its port.
Without a pull up resistor, USB assumes there is nothing connected to the bus. In order to help user to identify maximum speed of device, USB device often specify it's speed on it's
cover with one of USB special marketing logos.