USB connector standard (version 1.0 and 2.0) started with a USB type A connector with 4 contact pins. Then came the newer version USB 3.0 standard. The number of pins increases to support higher data transfer speed. The USB type A plug/receptacle is then redesigned with more pins, with physical compatibility when it is plugged with the older version of the USB type A connector.
USB Type A (USB version 2.0, version 1.0)
Pinout of the simple version of the USB plug/receptacle.
| Pin No. | Name | Description |
| 1 | 5V | 5V power supply |
| 2 | D- | Data -ve |
| 3 | D+ | Data +ve |
| 4 | Gnd | Ground |
USB Type A (USB version 3.0)
Pinout of the new USB 3.0 standard, design the type A connector (plug/receptable) to be backward compatible to the former USB 2.0 type A connector.
| Pin No. | Name | Description |
| 1 | 5V | Ground |
| 2 | D- | Data -ve |
| 3 | D+ | Data +ve |
| 4 | Gnd | Ground |
| 5 | Rx- | Receive, Shielded differential pair #1, negative |
| 6 | Rx+ | Receive, Shielded differential pair #1, positive |
| 7 | Gnd | Ground |
| 8 | Tx- | Transmit, Shielded differential pair #2, negative |
| 9 | Tx+ | Transmit, Shielded differential pair #2, positive |
