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The USB ports use USB Type A connectors, which have four pins each. Two of the pins are used for power and two for data. Figure 3-1 is an illustration of a Type A port; Table 1 shows the pin assignments.
Figure 3-1 USB Type A port and pins
| 1 | VCC | +5 VDC |
| 2 | D- | Data - |
| 3 | D+ | Data + |
| 4 | GND | Ground |
The iMac family computers provide 5-volt power to the USB ports. The maximum total current available is 500 mA on each port.
The USB ports support both low-speed and high-speed data transfers, at up to 1.5 Mbits per second and 12 Mbits per second, respectively. High-speed operation requires the use of shielded cables.
The iMac family computers come with version 1.3 of the Macintosh USB system software, which supports all four data transfer types defined in the USB specification.